Primeros pasos con Spanner en JDBC

Objetivos

En este tutorial se explican los siguientes pasos para usar el controlador JDBC de Spanner:

  • Crea una instancia y una base de datos de Spanner.
  • Escribir, leer y ejecutar consultas SQL sobre datos en la base de datos.
  • Actualizar el esquema de la base de datos.
  • Actualizar datos mediante una transacción de lectura y escritura.
  • Agregar un índice secundario a la base de datos.
  • Usar el índice para leer los datos y ejecutar consultas SQL sobre ellos.
  • Recuperar datos mediante una transacción de solo lectura.

Costes

En este tutorial se usa Spanner, que es un componente facturable deGoogle Cloud. Para obtener información sobre el coste de usar Spanner, consulta la página Precios.

Antes de empezar

Sigue los pasos que se describen en la sección Configuración, donde se explica cómo crear y definir un proyecto predeterminado Google Cloud , habilitar la facturación y la API Cloud Spanner, y configurar OAuth 2.0 para obtener las credenciales de autenticación que se usarán con la API Cloud Spanner.

En concreto, asegúrate de ejecutar gcloud auth application-default login para configurar tu entorno de desarrollo local con credenciales de autenticación.

Preparar el entorno JDBC local

  1. Instala los elementos indicados a continuación en la máquina de desarrollo si aún no están instalados:

  2. Clona el repositorio de aplicaciones de muestra en la máquina local:

    git clone https://github.com/googleapis/java-spanner-jdbc.git

  3. Cambia al directorio que contiene el código de ejemplo de Spanner:

    cd java-spanner-jdbc/samples/snippets

Crear una instancia

La primera vez que uses Spanner, debes crear una instancia, que es una asignación de recursos que utilizan las bases de datos de Spanner. Cuando creas una instancia, tienes que elegir una configuración de instancia, que determina dónde se almacenan tus datos y la cantidad de nodos que se van a usar, lo que permite conocer la cantidad de recursos de almacenamiento y publicación de la instancia.

Consulta Crear una instancia para saber cómo crear una instancia de Spanner con cualquiera de los siguientes métodos. Puedes llamar a tu instancia test-instance para usarla con otros temas de este documento que hagan referencia a una instancia llamada test-instance.

  • Google Cloud CLI
  • La Google Cloud consola
  • Una biblioteca de cliente (C++, C#, Go, Java, Node.js, PHP, Python o Ruby)

Consultar los archivos de muestra

El repositorio de ejemplos contiene un ejemplo que muestra cómo usar Spanner con JDBC.

El pom.xml añade el controlador JDBC de Spanner a las dependencias del proyecto y configura el complemento de ensamblaje para crear un archivo JAR ejecutable con la clase Java definida en este tutorial.

Compila el ejemplo desde el directorio samples/snippets:

mvn package -DskipTests

Crear una base de datos

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
createdatabase test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
createpgdatabase test-instance example-db

Deberías ver lo siguiente:

Created database [projects/my-project/instances/test-instance/databases/example-db]
El siguiente código crea una base de datos y dos tablas en ella.

GoogleSQL 

static void createDatabase(DatabaseAdminClient dbAdminClient,
    InstanceName instanceName, String databaseId) {
  CreateDatabaseRequest createDatabaseRequest =
      CreateDatabaseRequest.newBuilder()
          .setCreateStatement("CREATE DATABASE `" + databaseId + "`")
          .setParent(instanceName.toString())
          .addAllExtraStatements(Arrays.asList(
              "CREATE TABLE Singers ("
                  + "  SingerId   INT64 NOT NULL,"
                  + "  FirstName  STRING(1024),"
                  + "  LastName   STRING(1024),"
                  + "  SingerInfo BYTES(MAX),"
                  + "  FullName STRING(2048) AS "
                  + "  (ARRAY_TO_STRING([FirstName, LastName], \" \")) STORED"
                  + ") PRIMARY KEY (SingerId)",
              "CREATE TABLE Albums ("
                  + "  SingerId     INT64 NOT NULL,"
                  + "  AlbumId      INT64 NOT NULL,"
                  + "  AlbumTitle   STRING(MAX)"
                  + ") PRIMARY KEY (SingerId, AlbumId),"
                  + "  INTERLEAVE IN PARENT Singers ON DELETE CASCADE")).build();
  try {
    // Initiate the request which returns an OperationFuture.
    com.google.spanner.admin.database.v1.Database db =
        dbAdminClient.createDatabaseAsync(createDatabaseRequest).get();
    System.out.println("Created database [" + db.getName() + "]");
  } catch (ExecutionException e) {
    // If the operation failed during execution, expose the cause.
    throw (SpannerException) e.getCause();
  } catch (InterruptedException e) {
    // Throw when a thread is waiting, sleeping, or otherwise occupied,
    // and the thread is interrupted, either before or during the activity.
    throw SpannerExceptionFactory.propagateInterrupt(e);
  }
}

PostgreSQL 

static void createPostgreSqlDatabase(
    DatabaseAdminClient dbAdminClient, String projectId, String instanceId, String databaseId) {
  final CreateDatabaseRequest request =
      CreateDatabaseRequest.newBuilder()
          .setCreateStatement("CREATE DATABASE \"" + databaseId + "\"")
          .setParent(InstanceName.of(projectId, instanceId).toString())
          .setDatabaseDialect(DatabaseDialect.POSTGRESQL).build();

  try {
    // Initiate the request which returns an OperationFuture.
    Database db = dbAdminClient.createDatabaseAsync(request).get();
    System.out.println("Created database [" + db.getName() + "]");
  } catch (ExecutionException e) {
    // If the operation failed during execution, expose the cause.
    throw (SpannerException) e.getCause();
  } catch (InterruptedException e) {
    // Throw when a thread is waiting, sleeping, or otherwise occupied,
    // and the thread is interrupted, either before or during the activity.
    throw SpannerExceptionFactory.propagateInterrupt(e);
  }
}
static void createTableUsingDdl(DatabaseAdminClient dbAdminClient, DatabaseName databaseName) {
  try {
    // Initiate the request which returns an OperationFuture.
    dbAdminClient.updateDatabaseDdlAsync(
        databaseName,
        Arrays.asList(
            "CREATE TABLE Singers ("
                + "  SingerId   bigint NOT NULL,"
                + "  FirstName  character varying(1024),"
                + "  LastName   character varying(1024),"
                + "  SingerInfo bytea,"
                + "  FullName character varying(2048) GENERATED "
                + "  ALWAYS AS (FirstName || ' ' || LastName) STORED,"
                + "  PRIMARY KEY (SingerId)"
                + ")",
            "CREATE TABLE Albums ("
                + "  SingerId     bigint NOT NULL,"
                + "  AlbumId      bigint NOT NULL,"
                + "  AlbumTitle   character varying(1024),"
                + "  PRIMARY KEY (SingerId, AlbumId)"
                + ") INTERLEAVE IN PARENT Singers ON DELETE CASCADE")).get();
    System.out.println("Created Singers & Albums tables in database: [" + databaseName + "]");
  } catch (ExecutionException e) {
    // If the operation failed during execution, expose the cause.
    throw SpannerExceptionFactory.asSpannerException(e);
  } catch (InterruptedException e) {
    // Throw when a thread is waiting, sleeping, or otherwise occupied,
    // and the thread is interrupted, either before or during the activity.
    throw SpannerExceptionFactory.propagateInterrupt(e);
  }
}

El siguiente paso consiste en escribir datos en la base de datos.

Crear una conexión JDBC

Para poder leer o escribir datos, debes crear un Connection. Todas tus interacciones con Spanner deben realizarse a través de un Connection. El nombre de la base de datos y otras propiedades se especifican en la URL de conexión JDBC y en el conjunto java.util.Properties.

GoogleSQL 

static void createConnection(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  // Connection properties can be specified both with in a Properties object
  // and in the connection URL.
  properties.put("numChannels", "8");
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s"
                  + ";minSessions=400;maxSessions=400",
              project, instance, database),
          properties)) {
    try (ResultSet resultSet =
        connection.createStatement().executeQuery("select 'Hello World!'")) {
      while (resultSet.next()) {
        System.out.println(resultSet.getString(1));
      }
    }
  }
}

PostgreSQL 

static void createConnection(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  // Connection properties can be specified both with in a Properties object
  // and in the connection URL.
  properties.put("numChannels", "8");
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s"
                  + ";minSessions=400;maxSessions=400",
              project, instance, database),
          properties)) {
    try (ResultSet resultSet =
        connection.createStatement().executeQuery("select 'Hello World!'")) {
      while (resultSet.next()) {
        System.out.println(resultSet.getString(1));
      }
    }
  }
}

Para ver una lista completa de las propiedades admitidas, consulta Propiedades de URL de conexión.

Cada Connection usa recursos, por lo que es recomendable cerrar las conexiones cuando ya no se necesiten o usar un grupo de conexiones para reutilizarlas en toda la aplicación.

Consulta más información en la Connection referencia de Javadoc.

Conectar el controlador JDBC al emulador

Puedes conectar el controlador JDBC al emulador de Spanner de dos formas:

  • Define la variable de entorno SPANNER_EMULATOR_HOST: de esta forma, se indica al controlador JDBC que se conecte al emulador. La instancia y la base de datos de Spanner de la URL de conexión JDBC ya deben existir en el emulador.
  • Añade autoConfigEmulator=true a la URL de conexión: de esta forma, se indica al controlador JDBC que se conecte al emulador y que cree automáticamente la instancia y la base de datos de Spanner en la URL de conexión JDBC si no existen.

En este ejemplo se muestra cómo usar la opción de URL de conexión autoConfigEmulator=true.

GoogleSQL 

static void createConnectionWithEmulator(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  // Add autoConfigEmulator=true to the connection URL to instruct the JDBC
  // driver to connect to the Spanner emulator on localhost:9010.
  // The Spanner instance and database are automatically created if these
  // don't already exist.
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s"
                  + ";autoConfigEmulator=true",
              project, instance, database),
          properties)) {
    try (ResultSet resultSet =
        connection.createStatement().executeQuery("select 'Hello World!'")) {
      while (resultSet.next()) {
        System.out.println(resultSet.getString(1));
      }
    }
  }
}

PostgreSQL 

static void createConnectionWithEmulator(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  // Add autoConfigEmulator=true to the connection URL to instruct the JDBC
  // driver to connect to the Spanner emulator on localhost:9010.
  // The Spanner instance and database are automatically created if these
  // don't already exist.
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s"
                  + ";autoConfigEmulator=true",
              project, instance, database),
          properties)) {
    try (ResultSet resultSet =
        connection.createStatement().executeQuery("select 'Hello World!'")) {
      while (resultSet.next()) {
        System.out.println(resultSet.getString(1));
      }
    }
  }
}

Escribir datos con DML

Puedes insertar datos mediante el lenguaje de manipulación de datos (DML) en una transacción de lectura y escritura.

Utiliza el método PreparedStatement.executeUpdate() para ejecutar una instrucción DML.

GoogleSQL 

static void writeDataWithDml(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Add 4 rows in one statement.
    // JDBC always uses '?' as a parameter placeholder.
    try (PreparedStatement preparedStatement =
        connection.prepareStatement(
            "INSERT INTO Singers (SingerId, FirstName, LastName) VALUES "
                + "(?, ?, ?), "
                + "(?, ?, ?), "
                + "(?, ?, ?), "
                + "(?, ?, ?)")) {

      final ImmutableList<Singer> singers =
          ImmutableList.of(
              new Singer(/* SingerId = */ 12L, "Melissa", "Garcia"),
              new Singer(/* SingerId = */ 13L, "Russel", "Morales"),
              new Singer(/* SingerId = */ 14L, "Jacqueline", "Long"),
              new Singer(/* SingerId = */ 15L, "Dylan", "Shaw"));

      // Note that JDBC parameters start at index 1.
      int paramIndex = 0;
      for (Singer singer : singers) {
        preparedStatement.setLong(++paramIndex, singer.singerId);
        preparedStatement.setString(++paramIndex, singer.firstName);
        preparedStatement.setString(++paramIndex, singer.lastName);
      }

      int updateCount = preparedStatement.executeUpdate();
      System.out.printf("%d records inserted.\n", updateCount);
    }
  }
}

PostgreSQL 

static void writeDataWithDmlPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Add 4 rows in one statement.
    // JDBC always uses '?' as a parameter placeholder.
    try (PreparedStatement preparedStatement =
        connection.prepareStatement(
            "INSERT INTO singers (singer_id, first_name, last_name) VALUES "
                + "(?, ?, ?), "
                + "(?, ?, ?), "
                + "(?, ?, ?), "
                + "(?, ?, ?)")) {

      final ImmutableList<Singer> singers =
          ImmutableList.of(
              new Singer(/* SingerId = */ 12L, "Melissa", "Garcia"),
              new Singer(/* SingerId = */ 13L, "Russel", "Morales"),
              new Singer(/* SingerId = */ 14L, "Jacqueline", "Long"),
              new Singer(/* SingerId = */ 15L, "Dylan", "Shaw"));

      // Note that JDBC parameters start at index 1.
      int paramIndex = 0;
      for (Singer singer : singers) {
        preparedStatement.setLong(++paramIndex, singer.singerId);
        preparedStatement.setString(++paramIndex, singer.firstName);
        preparedStatement.setString(++paramIndex, singer.lastName);
      }

      int updateCount = preparedStatement.executeUpdate();
      System.out.printf("%d records inserted.\n", updateCount);
    }
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
writeusingdml test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
writeusingdmlpg test-instance example-db

Deberías ver lo siguiente:

4 records inserted.

Escribir datos con un lote de DML

Puedes usar los métodos PreparedStatement#addBatch() y PreparedStatement#executeBatch() para ejecutar varias instrucciones DML en un lote.

GoogleSQL 

static void writeDataWithDmlBatch(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Add multiple rows in one DML batch.
    // JDBC always uses '?' as a parameter placeholder.
    try (PreparedStatement preparedStatement =
        connection.prepareStatement(
            "INSERT INTO Singers (SingerId, FirstName, LastName) "
                + "VALUES (?, ?, ?)")) {
      final ImmutableList<Singer> singers =
          ImmutableList.of(
              new Singer(/* SingerId = */ 16L, "Sarah", "Wilson"),
              new Singer(/* SingerId = */ 17L, "Ethan", "Miller"),
              new Singer(/* SingerId = */ 18L, "Maya", "Patel"));

      for (Singer singer : singers) {
        // Note that JDBC parameters start at index 1.
        int paramIndex = 0;
        preparedStatement.setLong(++paramIndex, singer.singerId);
        preparedStatement.setString(++paramIndex, singer.firstName);
        preparedStatement.setString(++paramIndex, singer.lastName);
        preparedStatement.addBatch();
      }

      int[] updateCounts = preparedStatement.executeBatch();
      System.out.printf(
          "%d records inserted.\n",
          Arrays.stream(updateCounts).sum());
    }
  }
}

PostgreSQL 

static void writeDataWithDmlBatchPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Add multiple rows in one DML batch.
    // JDBC always uses '?' as a parameter placeholder.
    try (PreparedStatement preparedStatement =
        connection.prepareStatement(
            "INSERT INTO singers (singer_id, first_name, last_name)"
                + " VALUES (?, ?, ?)")) {
      final ImmutableList<Singer> singers =
          ImmutableList.of(
              new Singer(/* SingerId = */ 16L, "Sarah", "Wilson"),
              new Singer(/* SingerId = */ 17L, "Ethan", "Miller"),
              new Singer(/* SingerId = */ 18L, "Maya", "Patel"));

      for (Singer singer : singers) {
        // Note that JDBC parameters start at index 1.
        int paramIndex = 0;
        preparedStatement.setLong(++paramIndex, singer.singerId);
        preparedStatement.setString(++paramIndex, singer.firstName);
        preparedStatement.setString(++paramIndex, singer.lastName);
        preparedStatement.addBatch();
      }

      int[] updateCounts = preparedStatement.executeBatch();
      System.out.printf(
          "%d records inserted.\n",
          Arrays.stream(updateCounts).sum());
    }
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
writeusingdmlbatch test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
writeusingdmlbatchpg test-instance example-db

Deberías ver lo siguiente:

3 records inserted.

Escribir datos con mutaciones

También puedes insertar datos mediante mutaciones.

Puedes escribir datos con un objeto Mutation. Un objeto Mutation es un contenedor de operaciones de mutación. Una Mutation representa una secuencia de inserciones, actualizaciones y eliminaciones que Spanner aplica de forma atómica a diferentes filas y tablas de una base de datos de Spanner.

El método newInsertBuilder() de la clase Mutation crea una mutación INSERT, que inserta una fila nueva en una tabla. Si ya existe la fila, no se puede escribir. También puedes usar el método newInsertOrUpdateBuilder para crear una mutación INSERT_OR_UPDATE, que actualiza los valores de las columnas si la fila ya existe.

El método write() de la interfaz CloudSpannerJdbcConnection escribe las mutaciones. Todas las mutaciones de un mismo lote se aplican de forma atómica.

Puedes extraer la interfaz CloudSpannerJdbcConnection de un Connection de Spanner JDBC.

En este código se muestra cómo escribir los datos mediante mutaciones:

GoogleSQL 

/** The list of Singers to insert. */
static final List<Singer> SINGERS =
    Arrays.asList(
        new Singer(1, "Marc", "Richards"),
        new Singer(2, "Catalina", "Smith"),
        new Singer(3, "Alice", "Trentor"),
        new Singer(4, "Lea", "Martin"),
        new Singer(5, "David", "Lomond"));

/** The list of Albums to insert. */
static final List<Album> ALBUMS =
    Arrays.asList(
        new Album(1, 1, "Total Junk"),
        new Album(1, 2, "Go, Go, Go"),
        new Album(2, 1, "Green"),
        new Album(2, 2, "Forever Hold Your Peace"),
        new Album(2, 3, "Terrified"));

static void writeDataWithMutations(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Unwrap the CloudSpannerJdbcConnection interface
    // from the java.sql.Connection.
    CloudSpannerJdbcConnection cloudSpannerJdbcConnection =
        connection.unwrap(CloudSpannerJdbcConnection.class);

    List<Mutation> mutations = new ArrayList<>();
    for (Singer singer : SINGERS) {
      mutations.add(
          Mutation.newInsertBuilder("Singers")
              .set("SingerId")
              .to(singer.singerId)
              .set("FirstName")
              .to(singer.firstName)
              .set("LastName")
              .to(singer.lastName)
              .build());
    }
    for (Album album : ALBUMS) {
      mutations.add(
          Mutation.newInsertBuilder("Albums")
              .set("SingerId")
              .to(album.singerId)
              .set("AlbumId")
              .to(album.albumId)
              .set("AlbumTitle")
              .to(album.albumTitle)
              .build());
    }
    // Apply the mutations atomically to Spanner.
    cloudSpannerJdbcConnection.write(mutations);
    System.out.printf("Inserted %d rows.\n", mutations.size());
  }
}

PostgreSQL 

/** The list of Singers to insert. */
static final List<Singer> SINGERS =
    Arrays.asList(
        new Singer(1, "Marc", "Richards"),
        new Singer(2, "Catalina", "Smith"),
        new Singer(3, "Alice", "Trentor"),
        new Singer(4, "Lea", "Martin"),
        new Singer(5, "David", "Lomond"));

/** The list of Albums to insert. */
static final List<Album> ALBUMS =
    Arrays.asList(
        new Album(1, 1, "Total Junk"),
        new Album(1, 2, "Go, Go, Go"),
        new Album(2, 1, "Green"),
        new Album(2, 2, "Forever Hold Your Peace"),
        new Album(2, 3, "Terrified"));

static void writeDataWithMutationsPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Unwrap the CloudSpannerJdbcConnection interface
    // from the java.sql.Connection.
    CloudSpannerJdbcConnection cloudSpannerJdbcConnection =
        connection.unwrap(CloudSpannerJdbcConnection.class);

    List<Mutation> mutations = new ArrayList<>();
    for (Singer singer : SINGERS) {
      mutations.add(
          Mutation.newInsertBuilder("singers")
              .set("singer_id")
              .to(singer.singerId)
              .set("first_name")
              .to(singer.firstName)
              .set("last_name")
              .to(singer.lastName)
              .build());
    }
    for (Album album : ALBUMS) {
      mutations.add(
          Mutation.newInsertBuilder("albums")
              .set("singer_id")
              .to(album.singerId)
              .set("album_id")
              .to(album.albumId)
              .set("album_title")
              .to(album.albumTitle)
              .build());
    }
    // Apply the mutations atomically to Spanner.
    cloudSpannerJdbcConnection.write(mutations);
    System.out.printf("Inserted %d rows.\n", mutations.size());
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
write test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
writepg test-instance example-db

Deberías ver lo siguiente:

Inserted 10 rows.

Consultar datos mediante SQL

Spanner admite una interfaz SQL para leer datos, a la que puedes acceder en la línea de comandos mediante la CLI de Google Cloud o de forma programática mediante el controlador JDBC de Spanner.

En la línea de comandos

Ejecuta la siguiente instrucción SQL para leer los valores de todas las columnas de la tabla Albums:

GoogleSQL 

gcloud spanner databases execute-sql example-db --instance=test-instance \
    --sql='SELECT SingerId, AlbumId, AlbumTitle FROM Albums'

PostgreSQL 

gcloud spanner databases execute-sql example-db --instance=test-instance \
    --sql='SELECT singer_id, album_id, album_title FROM albums'

El resultado muestra lo siguiente:

SingerId AlbumId AlbumTitle
1        1       Total Junk
1        2       Go, Go, Go
2        1       Green
2        2       Forever Hold Your Peace
2        3       Terrified

Usar el controlador JDBC de Spanner

Además de ejecutar una instrucción SQL en la línea de comandos, puedes emitir la misma instrucción SQL de forma programática mediante el controlador JDBC de Spanner.

Los siguientes métodos y clases sirven para ejecutar la consulta SQL:

  • El método createStatement() de la interfaz Connection: úsalo para crear un objeto de instrucción para ejecutar una instrucción SQL.
  • El método executeQuery(String) de la clase Statement: usa este método para ejecutar una consulta en una base de datos.
  • La clase Statement: úsala para ejecutar una cadena de SQL.
  • La clase ResultSet: úsala para acceder a los datos devueltos por una instrucción SQL.

A continuación, se indica cómo emitir la consulta y acceder a los datos:

GoogleSQL 

static void queryData(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "SELECT SingerId, AlbumId, AlbumTitle "
                + "FROM Albums")) {
      while (resultSet.next()) {
        System.out.printf(
            "%d %d %s\n",
            resultSet.getLong("SingerId"),
            resultSet.getLong("AlbumId"),
            resultSet.getString("AlbumTitle"));
      }
    }
  }
}

PostgreSQL 

static void queryDataPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "SELECT singer_id, album_id, album_title "
                    + "FROM albums")) {
      while (resultSet.next()) {
        System.out.printf(
            "%d %d %s\n",
            resultSet.getLong("singer_id"),
            resultSet.getLong("album_id"),
            resultSet.getString("album_title"));
      }
    }
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
query test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
querypg test-instance example-db

El resultado debe ser el siguiente:

1 1 Total Junk
1 2 Go, Go, Go
2 1 Green
2 2 Forever Hold Your Peace
2 3 Terrified

Consultar usando un parámetro de SQL

Si tu aplicación tiene una consulta que se ejecuta con frecuencia, puedes mejorar su rendimiento parametrizándola. La consulta paramétrica resultante se puede almacenar en caché y reutilizar, lo que reduce los costes de compilación. Para obtener más información, consulta Usar parámetros de consulta para acelerar las consultas que se ejecutan con frecuencia.

Aquí tienes un ejemplo de cómo usar un parámetro en la cláusula WHERE para consultar registros que contengan un valor específico de LastName.

Usa java.sql.PreparedStatement para ejecutar una consulta con un parámetro.

GoogleSQL 

static void queryWithParameter(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    try (PreparedStatement statement =
        connection.prepareStatement(
            "SELECT SingerId, FirstName, LastName "
                + "FROM Singers "
                + "WHERE LastName = ?")) {
      statement.setString(1, "Garcia");
      try (ResultSet resultSet = statement.executeQuery()) {
        while (resultSet.next()) {
          System.out.printf(
              "%d %s %s\n",
              resultSet.getLong("SingerId"),
              resultSet.getString("FirstName"),
              resultSet.getString("LastName"));
        }
      }
    }
  }
}

PostgreSQL 

static void queryWithParameterPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    try (PreparedStatement statement =
        connection.prepareStatement(
            "SELECT singer_id, first_name, last_name "
                + "FROM singers "
                + "WHERE last_name = ?")) {
      statement.setString(1, "Garcia");
      try (ResultSet resultSet = statement.executeQuery()) {
        while (resultSet.next()) {
          System.out.printf(
              "%d %s %s\n",
              resultSet.getLong("singer_id"),
              resultSet.getString("first_name"),
              resultSet.getString("last_name"));
        }
      }
    }
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
querywithparameter test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
querywithparameterpg test-instance example-db

El resultado debe ser el siguiente:

12 Melissa Garcia

Actualizar el esquema de la base de datos

Supongamos que quiere añadir una nueva columna llamada MarketingBudget a la tabla Albums. Para agregar una nueva columna a una tabla existente, es preciso actualizar el esquema de base de datos. Spanner admite actualizaciones de esquemas en una base de datos mientras esta sigue atendiendo tráfico. Para actualizar el esquema, no es necesario desconectar la base de datos y no se bloquean tablas ni columnas completas. Puedes seguir escribiendo datos en la base de datos durante la actualización del esquema. Consulta más información sobre las actualizaciones de esquemas y el rendimiento de los cambios de esquemas admitidos en el artículo Hacer actualizaciones de esquemas.

Añadir una columna

Puedes añadir una columna en la línea de comandos mediante la CLI de Google Cloud o de forma programática mediante el controlador JDBC de Spanner.

En la línea de comandos

Usa el siguiente comando ALTER TABLE para añadir la nueva columna a la tabla:

GoogleSQL 

gcloud spanner databases ddl update example-db --instance=test-instance \
    --ddl='ALTER TABLE Albums ADD COLUMN MarketingBudget INT64'

PostgreSQL 

gcloud spanner databases ddl update example-db --instance=test-instance \
    --ddl='ALTER TABLE albums ADD COLUMN marketing_budget BIGINT'

Deberías ver lo siguiente:

Schema updating...done.

Usar el controlador JDBC de Spanner

Usa el método execute(String) de la clase java.sql.Statement para modificar el esquema:

GoogleSQL 

static void addColumn(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    connection
        .createStatement()
        .execute("ALTER TABLE Albums ADD COLUMN MarketingBudget INT64");
    System.out.println("Added MarketingBudget column");
  }
}

PostgreSQL 

static void addColumnPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    connection
        .createStatement()
        .execute("alter table albums add column marketing_budget bigint");
    System.out.println("Added marketing_budget column");
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
addmarketingbudget test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
addmarketingbudgetpg test-instance example-db

Deberías ver lo siguiente:

Added MarketingBudget column.

Ejecutar un lote de DDL

Se recomienda ejecutar varias modificaciones de esquema en un lote. Usa el método addBatch(String) de java.sql.Statement para añadir varias instrucciones DDL a un lote.

GoogleSQL 

static void ddlBatch(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    try (Statement statement = connection.createStatement()) {
      // Create two new tables in one batch.
      statement.addBatch(
          "CREATE TABLE Venues ("
              + "  VenueId     INT64 NOT NULL,"
              + "  Name        STRING(1024),"
              + "  Description JSON"
              + ") PRIMARY KEY (VenueId)");
      statement.addBatch(
          "CREATE TABLE Concerts ("
              + "  ConcertId INT64 NOT NULL,"
              + "  VenueId   INT64 NOT NULL,"
              + "  SingerId  INT64 NOT NULL,"
              + "  StartTime TIMESTAMP,"
              + "  EndTime   TIMESTAMP,"
              + "  CONSTRAINT Fk_Concerts_Venues FOREIGN KEY"
              + "    (VenueId) REFERENCES Venues (VenueId),"
              + "  CONSTRAINT Fk_Concerts_Singers FOREIGN KEY"
              + "    (SingerId) REFERENCES Singers (SingerId),"
              + ") PRIMARY KEY (ConcertId)");
      statement.executeBatch();
    }
    System.out.println("Added Venues and Concerts tables");
  }
}

PostgreSQL 

static void ddlBatchPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    try (Statement statement = connection.createStatement()) {
      // Create two new tables in one batch.
      statement.addBatch(
          "CREATE TABLE venues ("
              + "  venue_id    bigint not null primary key,"
              + "  name        varchar(1024),"
              + "  description jsonb"
              + ")");
      statement.addBatch(
          "CREATE TABLE concerts ("
              + "  concert_id bigint not null primary key ,"
              + "  venue_id   bigint not null,"
              + "  singer_id  bigint not null,"
              + "  start_time timestamptz,"
              + "  end_time   timestamptz,"
              + "  constraint fk_concerts_venues foreign key"
              + "    (venue_id) references venues (venue_id),"
              + "  constraint fk_concerts_singers foreign key"
              + "    (singer_id) references singers (singer_id)"
              + ")");
      statement.executeBatch();
    }
    System.out.println("Added venues and concerts tables");
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
ddlbatch test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
ddlbatchpg test-instance example-db

Deberías ver lo siguiente:

Added Venues and Concerts tables.

Escribir datos en la nueva columna

El siguiente código sirve para escribir datos en la nueva columna. Define MarketingBudget como 100000 en la fila con la clave Albums(1, 1) y como 500000 en la fila con la clave Albums(2, 2).

GoogleSQL 

static void updateDataWithMutations(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Unwrap the CloudSpannerJdbcConnection interface
    // from the java.sql.Connection.
    CloudSpannerJdbcConnection cloudSpannerJdbcConnection =
        connection.unwrap(CloudSpannerJdbcConnection.class);

    final long marketingBudgetAlbum1 = 100000L;
    final long marketingBudgetAlbum2 = 500000L;
    // Mutation can be used to update/insert/delete a single row in a table.
    // Here we use newUpdateBuilder to create update mutations.
    List<Mutation> mutations =
        Arrays.asList(
            Mutation.newUpdateBuilder("Albums")
                .set("SingerId")
                .to(1)
                .set("AlbumId")
                .to(1)
                .set("MarketingBudget")
                .to(marketingBudgetAlbum1)
                .build(),
            Mutation.newUpdateBuilder("Albums")
                .set("SingerId")
                .to(2)
                .set("AlbumId")
                .to(2)
                .set("MarketingBudget")
                .to(marketingBudgetAlbum2)
                .build());
    // This writes all the mutations to Cloud Spanner atomically.
    cloudSpannerJdbcConnection.write(mutations);
    System.out.println("Updated albums");
  }
}

PostgreSQL 

static void updateDataWithMutationsPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Unwrap the CloudSpannerJdbcConnection interface
    // from the java.sql.Connection.
    CloudSpannerJdbcConnection cloudSpannerJdbcConnection =
        connection.unwrap(CloudSpannerJdbcConnection.class);

    final long marketingBudgetAlbum1 = 100000L;
    final long marketingBudgetAlbum2 = 500000L;
    // Mutation can be used to update/insert/delete a single row in a table.
    // Here we use newUpdateBuilder to create update mutations.
    List<Mutation> mutations =
        Arrays.asList(
            Mutation.newUpdateBuilder("albums")
                .set("singer_id")
                .to(1)
                .set("album_id")
                .to(1)
                .set("marketing_budget")
                .to(marketingBudgetAlbum1)
                .build(),
            Mutation.newUpdateBuilder("albums")
                .set("singer_id")
                .to(2)
                .set("album_id")
                .to(2)
                .set("marketing_budget")
                .to(marketingBudgetAlbum2)
                .build());
    // This writes all the mutations to Cloud Spanner atomically.
    cloudSpannerJdbcConnection.write(mutations);
    System.out.println("Updated albums");
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
update test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
updatepg test-instance example-db

Debería ver un resultado similar a este:

Updated albums

También puedes ejecutar una consulta SQL o una llamada de lectura para recuperar los valores que acabas de escribir.

Aquí está el código para ejecutar la consulta:

GoogleSQL 

static void queryDataWithNewColumn(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Rows without an explicit value for MarketingBudget will have a
    // MarketingBudget equal to null.
    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "SELECT SingerId, AlbumId, MarketingBudget "
                + "FROM Albums")) {
      while (resultSet.next()) {
        // Use the ResultSet#getObject(String) method to get data
        // of any type from the ResultSet.
        System.out.printf(
            "%s %s %s\n",
            resultSet.getObject("SingerId"),
            resultSet.getObject("AlbumId"),
            resultSet.getObject("MarketingBudget"));
      }
    }
  }
}

PostgreSQL 

static void queryDataWithNewColumnPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Rows without an explicit value for marketing_budget will have a
    // marketing_budget equal to null.
    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "select singer_id, album_id, marketing_budget "
                    + "from albums")) {
      while (resultSet.next()) {
        // Use the ResultSet#getObject(String) method to get data
        // of any type from the ResultSet.
        System.out.printf(
            "%s %s %s\n",
            resultSet.getObject("singer_id"),
            resultSet.getObject("album_id"),
            resultSet.getObject("marketing_budget"));
      }
    }
  }
}

Para ejecutar esta consulta, ejecuta el siguiente comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
querymarketingbudget test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
querymarketingbudgetpg test-instance example-db

El resultado muestra lo siguiente:

1 1 100000
1 2 null
2 1 null
2 2 500000
2 3 null

Actualizar datos

Puedes actualizar datos mediante DML en una transacción de lectura y escritura.

Define AutoCommit=false para ejecutar transacciones de lectura y escritura en JDBC.

GoogleSQL 

static void writeWithTransactionUsingDml(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Set AutoCommit=false to enable transactions.
    connection.setAutoCommit(false);

    // Transfer marketing budget from one album to another.
    // We do it in a transaction to ensure that the transfer is atomic.
    // There is no need to explicitly start the transaction. The first
    // statement on the connection will start a transaction when
    // AutoCommit=false.
    String selectMarketingBudgetSql =
        "SELECT MarketingBudget "
        + "FROM Albums "
        + "WHERE SingerId = ? AND AlbumId = ?";
    long album2Budget = 0;
    try (PreparedStatement selectMarketingBudgetStatement =
        connection.prepareStatement(selectMarketingBudgetSql)) {
      // Bind the query parameters to SingerId=2 and AlbumId=2.
      selectMarketingBudgetStatement.setLong(1, 2);
      selectMarketingBudgetStatement.setLong(2, 2);
      try (ResultSet resultSet =
          selectMarketingBudgetStatement.executeQuery()) {
        while (resultSet.next()) {
          album2Budget = resultSet.getLong("MarketingBudget");
        }
      }
      // The transaction will only be committed if this condition still holds
      // at the time of commit. Otherwise, the transaction will be aborted.
      final long transfer = 200000;
      if (album2Budget >= transfer) {
        long album1Budget = 0;
        // Re-use the existing PreparedStatement for selecting the
        // MarketingBudget to get the budget for Album 1.
        // Bind the query parameters to SingerId=1 and AlbumId=1.
        selectMarketingBudgetStatement.setLong(1, 1);
        selectMarketingBudgetStatement.setLong(2, 1);
        try (ResultSet resultSet =
            selectMarketingBudgetStatement.executeQuery()) {
          while (resultSet.next()) {
            album1Budget = resultSet.getLong("MarketingBudget");
          }
        }

        // Transfer part of the marketing budget of Album 2 to Album 1.
        album1Budget += transfer;
        album2Budget -= transfer;
        String updateSql =
            "UPDATE Albums "
                + "SET MarketingBudget = ? "
                + "WHERE SingerId = ? and AlbumId = ?";
        try (PreparedStatement updateStatement =
            connection.prepareStatement(updateSql)) {
          // Update Album 1.
          int paramIndex = 0;
          updateStatement.setLong(++paramIndex, album1Budget);
          updateStatement.setLong(++paramIndex, 1);
          updateStatement.setLong(++paramIndex, 1);
          // Create a DML batch by calling addBatch on
          // the current PreparedStatement.
          updateStatement.addBatch();

          // Update Album 2 in the same DML batch.
          paramIndex = 0;
          updateStatement.setLong(++paramIndex, album2Budget);
          updateStatement.setLong(++paramIndex, 2);
          updateStatement.setLong(++paramIndex, 2);
          updateStatement.addBatch();

          // Execute both DML statements in one batch.
          updateStatement.executeBatch();
        }
      }
    }
    // Commit the current transaction.
    connection.commit();
    System.out.println(
        "Transferred marketing budget from Album 2 to Album 1");
  }
}

PostgreSQL 

static void writeWithTransactionUsingDmlPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Set AutoCommit=false to enable transactions.
    connection.setAutoCommit(false);

    // Transfer marketing budget from one album to another. We do it in a
    // transaction to ensure that the transfer is atomic. There is no need
    // to explicitly start the transaction. The first statement on the
    // connection will start a transaction when AutoCommit=false.
    String selectMarketingBudgetSql =
        "SELECT marketing_budget "
            + "from albums "
            + "WHERE singer_id = ? and album_id = ?";
    long album2Budget = 0;
    try (PreparedStatement selectMarketingBudgetStatement =
        connection.prepareStatement(selectMarketingBudgetSql)) {
      // Bind the query parameters to SingerId=2 and AlbumId=2.
      selectMarketingBudgetStatement.setLong(1, 2);
      selectMarketingBudgetStatement.setLong(2, 2);
      try (ResultSet resultSet =
          selectMarketingBudgetStatement.executeQuery()) {
        while (resultSet.next()) {
          album2Budget = resultSet.getLong("marketing_budget");
        }
      }
      // The transaction will only be committed if this condition still holds
      // at the time of commit. Otherwise, the transaction will be aborted.
      final long transfer = 200000;
      if (album2Budget >= transfer) {
        long album1Budget = 0;
        // Re-use the existing PreparedStatement for selecting the
        // marketing_budget to get the budget for Album 1.
        // Bind the query parameters to SingerId=1 and AlbumId=1.
        selectMarketingBudgetStatement.setLong(1, 1);
        selectMarketingBudgetStatement.setLong(2, 1);
        try (ResultSet resultSet =
            selectMarketingBudgetStatement.executeQuery()) {
          while (resultSet.next()) {
            album1Budget = resultSet.getLong("marketing_budget");
          }
        }

        // Transfer part of the marketing budget of Album 2 to Album 1.
        album1Budget += transfer;
        album2Budget -= transfer;
        String updateSql =
            "UPDATE albums "
                + "SET marketing_budget = ? "
                + "WHERE singer_id = ? and album_id = ?";
        try (PreparedStatement updateStatement =
            connection.prepareStatement(updateSql)) {
          // Update Album 1.
          int paramIndex = 0;
          updateStatement.setLong(++paramIndex, album1Budget);
          updateStatement.setLong(++paramIndex, 1);
          updateStatement.setLong(++paramIndex, 1);
          // Create a DML batch by calling addBatch
          // on the current PreparedStatement.
          updateStatement.addBatch();

          // Update Album 2 in the same DML batch.
          paramIndex = 0;
          updateStatement.setLong(++paramIndex, album2Budget);
          updateStatement.setLong(++paramIndex, 2);
          updateStatement.setLong(++paramIndex, 2);
          updateStatement.addBatch();

          // Execute both DML statements in one batch.
          updateStatement.executeBatch();
        }
      }
    }
    // Commit the current transaction.
    connection.commit();
    System.out.println(
        "Transferred marketing budget from Album 2 to Album 1");
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
writewithtransactionusingdml test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
writewithtransactionusingdmlpg test-instance example-db

Etiquetas de transacción y de solicitud

Usa etiquetas de transacción y de solicitud para solucionar problemas de transacciones y consultas en Spanner. Puede definir etiquetas de transacción y de solicitud en JDBC con las variables de sesión TRANSACTION_TAG y STATEMENT_TAG.

GoogleSQL 

static void tags(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Set AutoCommit=false to enable transactions.
    connection.setAutoCommit(false);
    // Set the TRANSACTION_TAG session variable to set a transaction tag
    // for the current transaction.
    connection
        .createStatement()
        .execute("SET TRANSACTION_TAG='example-tx-tag'");

    // Set the STATEMENT_TAG session variable to set the request tag
    // that should be included with the next SQL statement.
    connection
        .createStatement()
        .execute("SET STATEMENT_TAG='query-marketing-budget'");
    long marketingBudget = 0L;
    long singerId = 1L;
    long albumId = 1L;
    try (PreparedStatement statement = connection.prepareStatement(
        "SELECT MarketingBudget "
        + "FROM Albums "
        + "WHERE SingerId=? AND AlbumId=?")) {
      statement.setLong(1, singerId);
      statement.setLong(2, albumId);
      try (ResultSet albumResultSet = statement.executeQuery()) {
        while (albumResultSet.next()) {
          marketingBudget = albumResultSet.getLong(1);
        }
      }
    }
    // Reduce the marketing budget by 10% if it is more than 1,000.
    final long maxMarketingBudget = 1000L;
    final float reduction = 0.1f;
    if (marketingBudget > maxMarketingBudget) {
      marketingBudget -= (long) (marketingBudget * reduction);
      connection
          .createStatement()
          .execute("SET STATEMENT_TAG='reduce-marketing-budget'");
      try (PreparedStatement statement = connection.prepareStatement(
          "UPDATE Albums SET MarketingBudget=? "
              + "WHERE SingerId=? AND AlbumId=?")) {
        int paramIndex = 0;
        statement.setLong(++paramIndex, marketingBudget);
        statement.setLong(++paramIndex, singerId);
        statement.setLong(++paramIndex, albumId);
        statement.executeUpdate();
      }
    }

    // Commit the current transaction.
    connection.commit();
    System.out.println("Reduced marketing budget");
  }
}

PostgreSQL 

static void tagsPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Set AutoCommit=false to enable transactions.
    connection.setAutoCommit(false);
    // Set the TRANSACTION_TAG session variable to set a transaction tag
    // for the current transaction.
    connection
        .createStatement()
        .execute("set spanner.transaction_tag='example-tx-tag'");

    // Set the STATEMENT_TAG session variable to set the request tag
    // that should be included with the next SQL statement.
    connection
        .createStatement()
        .execute("set spanner.statement_tag='query-marketing-budget'");
    long marketingBudget = 0L;
    long singerId = 1L;
    long albumId = 1L;
    try (PreparedStatement statement = connection.prepareStatement(
        "select marketing_budget "
            + "from albums "
            + "where singer_id=? and album_id=?")) {
      statement.setLong(1, singerId);
      statement.setLong(2, albumId);
      try (ResultSet albumResultSet = statement.executeQuery()) {
        while (albumResultSet.next()) {
          marketingBudget = albumResultSet.getLong(1);
        }
      }
    }
    // Reduce the marketing budget by 10% if it is more than 1,000.
    final long maxMarketingBudget = 1000L;
    final float reduction = 0.1f;
    if (marketingBudget > maxMarketingBudget) {
      marketingBudget -= (long) (marketingBudget * reduction);
      connection
          .createStatement()
          .execute("set spanner.statement_tag='reduce-marketing-budget'");
      try (PreparedStatement statement = connection.prepareStatement(
          "update albums set marketing_budget=? "
              + "where singer_id=? AND album_id=?")) {
        int paramIndex = 0;
        statement.setLong(++paramIndex, marketingBudget);
        statement.setLong(++paramIndex, singerId);
        statement.setLong(++paramIndex, albumId);
        statement.executeUpdate();
      }
    }

    // Commit the current transaction.
    connection.commit();
    System.out.println("Reduced marketing budget");
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
tags test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
tagspg test-instance example-db

Recuperar datos mediante transacciones de solo lectura

Supongamos que deseas ejecutar más de una lectura en la misma marca de tiempo. En las transacciones de solo lectura se observa un prefijo uniforme del historial de confirmación de transacción, por lo que la aplicación siempre obtiene datos uniformes. Define ReadOnly=true y AutoCommit=false en un java.sql.Connection o usa la instrucción SQL SET TRANSACTION READ ONLY para ejecutar una transacción de solo lectura.

A continuación, se muestra cómo ejecutar una consulta y realizar una lectura en la misma transacción de solo lectura:

GoogleSQL 

static void readOnlyTransaction(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Set AutoCommit=false to enable transactions.
    connection.setAutoCommit(false);
    // This SQL statement instructs the JDBC driver to use
    // a read-only transaction.
    connection.createStatement().execute("SET TRANSACTION READ ONLY");

    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "SELECT SingerId, AlbumId, AlbumTitle "
                    + "FROM Albums "
                    + "ORDER BY SingerId, AlbumId")) {
      while (resultSet.next()) {
        System.out.printf(
            "%d %d %s\n",
            resultSet.getLong("SingerId"),
            resultSet.getLong("AlbumId"),
            resultSet.getString("AlbumTitle"));
      }
    }
    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "SELECT SingerId, AlbumId, AlbumTitle "
                    + "FROM Albums "
                    + "ORDER BY AlbumTitle")) {
      while (resultSet.next()) {
        System.out.printf(
            "%d %d %s\n",
            resultSet.getLong("SingerId"),
            resultSet.getLong("AlbumId"),
            resultSet.getString("AlbumTitle"));
      }
    }
    // End the read-only transaction by calling commit().
    connection.commit();
  }
}

PostgreSQL 

static void readOnlyTransactionPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Set AutoCommit=false to enable transactions.
    connection.setAutoCommit(false);
    // This SQL statement instructs the JDBC driver to use
    // a read-only transaction.
    connection.createStatement().execute("set transaction read only");

    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "SELECT singer_id, album_id, album_title "
                    + "FROM albums "
                    + "ORDER BY singer_id, album_id")) {
      while (resultSet.next()) {
        System.out.printf(
            "%d %d %s\n",
            resultSet.getLong("singer_id"),
            resultSet.getLong("album_id"),
            resultSet.getString("album_title"));
      }
    }
    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "SELECT singer_id, album_id, album_title "
                    + "FROM albums "
                    + "ORDER BY album_title")) {
      while (resultSet.next()) {
        System.out.printf(
            "%d %d %s\n",
            resultSet.getLong("singer_id"),
            resultSet.getLong("album_id"),
            resultSet.getString("album_title"));
      }
    }
    // End the read-only transaction by calling commit().
    connection.commit();
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
readonlytransaction test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
readonlytransactionpg test-instance example-db

El resultado que verás debe parecerse al siguiente:

    1 1 Total Junk
    1 2 Go, Go, Go
    2 1 Green
    2 2 Forever Hold Your Peace
    2 3 Terrified
    2 2 Forever Hold Your Peace
    1 2 Go, Go, Go
    2 1 Green
    2 3 Terrified
    1 1 Total Junk

Consultas con particiones y Acelerador de datos

La API partitionQuery divide una consulta en partes más pequeñas, o particiones, y usa varias máquinas para obtener las particiones en paralelo. Cada partición se identifica mediante un token de partición. La API PartitionQuery tiene una latencia mayor que la API de consulta estándar, ya que solo está diseñada para operaciones en bloque, como exportar o analizar toda la base de datos.

Data Boost te permite ejecutar consultas analíticas y exportaciones de datos con un impacto casi nulo en las cargas de trabajo de la instancia de Spanner aprovisionada. Data Boost solo admite consultas particionadas.

GoogleSQL 

static void dataBoost(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // This enables Data Boost for all partitioned queries on this connection.
    connection.createStatement().execute("SET DATA_BOOST_ENABLED=TRUE");

    // Run a partitioned query. This query will use Data Boost.
    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "RUN PARTITIONED QUERY "
                    + "SELECT SingerId, FirstName, LastName "
                    + "FROM Singers")) {
      while (resultSet.next()) {
        System.out.printf(
            "%d %s %s\n",
            resultSet.getLong("SingerId"),
            resultSet.getString("FirstName"),
            resultSet.getString("LastName"));
      }
    }
  }
}

PostgreSQL 

static void dataBoostPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // This enables Data Boost for all partitioned queries on this connection.
    connection
        .createStatement()
        .execute("set spanner.data_boost_enabled=true");

    // Run a partitioned query. This query will use Data Boost.
    try (ResultSet resultSet =
        connection
            .createStatement()
            .executeQuery(
                "run partitioned query "
                    + "select singer_id, first_name, last_name "
                    + "from singers")) {
      while (resultSet.next()) {
        System.out.printf(
            "%d %s %s\n",
            resultSet.getLong("singer_id"),
            resultSet.getString("first_name"),
            resultSet.getString("last_name"));
      }
    }
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
databoost test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
databoostpg test-instance example-db

Para obtener más información sobre cómo ejecutar consultas con particiones y usar Data Boost con el controlador JDBC, consulta los siguientes artículos:

DML particionado

El lenguaje de manipulación de datos (DML) particionado se ha diseñado para los siguientes tipos de actualizaciones y eliminaciones en bloque:

  • Limpieza periódica y recolección de elementos no utilizados.
  • Rellenar las nuevas columnas con valores predeterminados.
* { GoogleSQL }

static void partitionedDml(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Enable Partitioned DML on this connection.
    connection
        .createStatement()
        .execute("SET AUTOCOMMIT_DML_MODE='PARTITIONED_NON_ATOMIC'");
    // Back-fill a default value for the MarketingBudget column.
    long lowerBoundUpdateCount =
        connection
            .createStatement()
            .executeUpdate("UPDATE Albums "
                + "SET MarketingBudget=0 "
                + "WHERE MarketingBudget IS NULL");
    System.out.printf("Updated at least %d albums\n", lowerBoundUpdateCount);
  }
}

PostgreSQL 

static void partitionedDmlPostgreSQL(
    final String project,
    final String instance,
    final String database,
    final Properties properties) throws SQLException {
  try (Connection connection =
      DriverManager.getConnection(
          String.format(
              "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
              project, instance, database),
          properties)) {
    // Enable Partitioned DML on this connection.
    connection
        .createStatement()
        .execute("set spanner.autocommit_dml_mode='partitioned_non_atomic'");
    // Back-fill a default value for the MarketingBudget column.
    long lowerBoundUpdateCount =
        connection
            .createStatement()
            .executeUpdate("update albums "
                + "set marketing_budget=0 "
                + "where marketing_budget is null");
    System.out.printf("Updated at least %d albums\n", lowerBoundUpdateCount);
  }
}

Ejecuta la muestra con este comando:

GoogleSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
pdml test-instance example-db

PostgreSQL 

java -jar target/jdbc-snippets/jdbc-samples.jar \
pdmlpg test-instance example-db

Para obtener más información sobre AUTOCOMMIT_DML_MODE, consulta:

Limpieza

Para evitar que se apliquen cargos adicionales en tu cuenta de Facturación de Cloud por los recursos utilizados en este tutorial, elimina la base de datos y la instancia que has creado.

Eliminar la base de datos

Al eliminar una instancia, se eliminan automáticamente todas sus bases de datos. En este paso se muestra cómo eliminar una base de datos sin eliminar una instancia (se seguirían generando costes por la instancia).

En la línea de comandos

gcloud spanner databases delete example-db --instance=test-instance

Usar la Google Cloud consola

  1. Ve a la página Instancias de Spanner de la Google Cloud consola.

    Ir a la página Instancias

  2. Haz clic en la instancia.

  3. Haz clic en la base de datos que quieras eliminar.

  4. En la página sobre detalles de la base de datos, haz clic en Eliminar.

  5. Confirma que deseas eliminar la base de datos y haz clic en Eliminar.

Eliminar la instancia

Al eliminar una instancia, se borran todas las bases de datos creadas en dicha instancia.

En la línea de comandos

gcloud spanner instances delete test-instance

Usar la Google Cloud consola

  1. Ve a la página Instancias de Spanner de la Google Cloud consola.

    Ir a la página Instancias

  2. Haz clic en tu instancia.

  3. Haz clic en Eliminar.

  4. Confirma que deseas eliminar la instancia y haz clic en Eliminar.

Siguientes pasos