Interface ReadContext (6.83.0)

A concurrency context in which to run a read or SQL statement. All ReadContexts are implicitly bound to a Session and therefore a particular Database.

Analyzes a query and returns query plan and/or query execution statistics information.

The query plan and query statistics information is contained in com.google.spanner.v1.ResultSetStats that can be accessed by calling ResultSet#getStats() on the returned ResultSet.

 ReadContext rc = dbClient.singleUse();
 ResultSet resultSet =
     rc.analyzeQuery(
         Statement.of("SELECT SingerId, AlbumId, MarketingBudget FROM Albums"),
         ReadContext.QueryAnalyzeMode.PROFILE);
 while (resultSet.next()) {
   // Discard the results. We're only processing because getStats() below requires it.
   resultSet.getCurrentRowAsStruct();
 }
 ResultSetStats stats = resultSet.getStats();
 

Closes this read context and frees up the underlying resources.

Executes a query against the database. Can also execute a DML statement with returning clause in a read/write transaction.

Implementations may or may not block in the initial executeQuery(...) call; for those that do not, the remote call will be initiated immediately but blocking on the response is deferred to the first ResultSet#next() call. Regardless of blocking behavior, any SpannerException is deferred to the first or subsequent ResultSet#next() call.

 // Rows without an explicit value for MarketingBudget will have a MarketingBudget equal to
 // null.
 ReadContext readContext = dbClient.singleUse();
 ResultSet resultSet =
     readContext.executeQuery(
         Statement.of(
             "SELECT SingerId, AlbumId, MarketingBudget, LastUpdateTime FROM Albums"));
 

Same as #executeQuery(Statement, QueryOption...), but is guaranteed to be non-blocking and returns its results as an AsyncResultSet.

Reads zero or more rows from a database.

Implementations may or may not block in the initial read(...) call; for those that do not, the remote call will be initiated immediately but blocking on the response is deferred to the first ResultSet#next() call. Regardless of blocking behavior, any SpannerException is deferred to the first or subsequent ResultSet#next() call.

 ReadContext readContext = dbClient.singleUse();
 ResultSet resultSet =
     readContext.read(
         "Albums",
         // KeySet.all() can be used to read all rows in a table. KeySet exposes other
         // methods to read only a subset of the table.
         KeySet.all(),
         Arrays.asList("SingerId", "AlbumId", "AlbumTitle"));
 

Same as #read(String, KeySet, Iterable, ReadOption...), but is guaranteed to be non-blocking and will return the results as an AsyncResultSet.

Reads a single row from a database, returning null if the row does not exist.

 ReadContext readContext = dbClient.singleUse();
 Struct row =
     readContext.readRow("Albums", Key.of(2, 1), Arrays.asList("MarketingBudget"));
 

Same as #readRow(String, Key, Iterable), but is guaranteed to be non-blocking.

Reads a single row from a database using an index, returning null if the row does not exist.

 ReadContext readContext = dbClient.singleUse();
 Struct row =
     readContext.readRowUsingIndex("Albums", "AlbumsByAlbumId", Key.of(1, "Green"),
         Arrays.asList("AlbumId", "AlbumTitle"));
 

Same as #readRowUsingIndex(String, String, Key, Iterable), but is guaranteed to be non-blocking.

Reads zero or more rows from a database using an index.

Implementations may or may not block in the initial read(...) call; for those that do not, the remote call will be initiated immediately but blocking on the response is deferred to the first ResultSet#next() call. Regardless of blocking behavior, any SpannerException is deferred to the first or subsequent ResultSet#next() call.

 ReadContext readContext = dbClient.singleUse();
 Struct row =
     readContext.readRowUsingIndex("Albums", "AlbumsByAlbumId", Key.of(1, "Green"),
         Arrays.asList("AlbumId", "AlbumTitle"));
 

Same as #readUsingIndex(String, String, KeySet, Iterable, ReadOption...), but is guaranteed to be non-blocking and will return its results as an AsyncResultSet.