Class Snapshot (3.51.0) 

Snapshot(
    session,
    read_timestamp=None,
    min_read_timestamp=None,
    max_staleness=None,
    exact_staleness=None,
    multi_use=False,
    transaction_id=None,
)

Allow a set of reads / SQL statements with shared staleness.

See https://cloud.google.com/spanner/reference/rpc/google.spanner.v1#google.spanner.v1.TransactionOptions.ReadOnly

If no options are passed, reads will use the strong model, reading at a timestamp where all previously committed transactions are visible.

Parameters
Name Description
session Session

The session used to perform the commit.
read_timestamp datetime.datetime

Execute all reads at the given timestamp.
min_read_timestamp datetime.datetime

Execute all reads at a timestamp >= min_read_timestamp.
max_staleness datetime.timedelta

Read data at a timestamp >= NOW - max_staleness seconds.
exact_staleness datetime.timedelta

Execute all reads at a timestamp that is exact_staleness old.
multi_use bool

If true, multiple read / execute_sql calls can be performed with the snapshot in the context of a read-only transaction, used to ensure isolation / consistency. Incompatible with max_staleness and min_read_timestamp.

Methods

begin

begin()

Begin a read-only transaction on the database.

Exceptions
Type Description
ValueError if the transaction is already begun, committed, or rolled back.
Returns
Type Description
bytes the ID for the newly-begun transaction.

execute_sql

execute_sql(
    sql,
    params=None,
    param_types=None,
    query_mode=None,
    query_options=None,
    request_options=None,
    partition=None,
    retry=_MethodDefault._DEFAULT_VALUE,
    timeout=_MethodDefault._DEFAULT_VALUE,
    data_boost_enabled=False,
    directed_read_options=None,
    column_info=None,
    lazy_decode=False,
)

Perform an ExecuteStreamingSql API request.

Parameters
Name Description
sql str

SQL query statement
params dict, {str -> column value}

values for parameter replacement. Keys must match the names used in sql.
param_types dict[str -> Union[dict, .types.Type]]

(Optional) maps explicit types for one or more param values; required if parameters are passed.
query_mode QueryMode

Mode governing return of results / query plan. See: QueryMode https://cloud.google.com/spanner/reference/rpc/google.spanner.v1#google.spanner.v1.ExecuteSqlRequest.QueryMode_.
query_options QueryOptions or dict

(Optional) Query optimizer configuration to use for the given query. If a dict is provided, it must be of the same form as the protobuf message QueryOptions
request_options RequestOptions

(Optional) Common options for this request. If a dict is provided, it must be of the same form as the protobuf message RequestOptions.
partition bytes

(Optional) one of the partition tokens returned from partition_query.
retry google.api_core.retry.Retry

(Optional) The retry settings for this request.
timeout float

(Optional) The timeout for this request.
directed_read_options DirectedReadOptions or dict

(Optional) Request level option used to set the directed_read_options for all ReadRequests and ExecuteSqlRequests that indicates which replicas or regions should be used for non-transactional reads or queries.
column_info dict

(Optional) dict of mapping between column names and additional column information. An object where column names as keys and custom objects as corresponding values for deserialization. It's specifically useful for data types like protobuf where deserialization logic is on user-specific code. When provided, the custom object enables deserialization of backend-received column data. If not provided, data remains serialized as bytes for Proto Messages and integer for Proto Enums.
lazy_decode bool

(Optional) If this argument is set to true, the iterator returns the underlying protobuf values instead of decoded Python objects. This reduces the time that is needed to iterate through large result sets. The application is responsible for decoding the data that is needed. The returned row iterator contains two functions that can be used for this. iterator.decode_row(row) decodes all the columns in the given row to an array of Python objects. iterator.decode_column(row, column_index) decodes one specific column in the given row.
Exceptions
Type Description
ValueError for reuse of single-use snapshots, or if a transaction ID is already pending for multiple-use snapshots.
Returns
Type Description
StreamedResultSet a result set instance which can be used to consume rows.

partition_query

partition_query(
    sql,
    params=None,
    param_types=None,
    partition_size_bytes=None,
    max_partitions=None,
    *,
    retry=_MethodDefault._DEFAULT_VALUE,
    timeout=_MethodDefault._DEFAULT_VALUE
)

Perform a PartitionQuery API request.

Parameters
Name Description
sql str

SQL query statement
params dict, {str -> column value}

values for parameter replacement. Keys must match the names used in sql.
param_types dict[str -> Union[dict, .types.Type]]

(Optional) maps explicit types for one or more param values; required if parameters are passed.
partition_size_bytes int

(Optional) desired size for each partition generated. The service uses this as a hint, the actual partition size may differ.
max_partitions int

(Optional) desired maximum number of partitions generated. The service uses this as a hint, the actual number of partitions may differ.
retry google.api_core.retry.Retry

(Optional) The retry settings for this request.
timeout float

(Optional) The timeout for this request.
Exceptions
Type Description
ValueError for single-use snapshots, or if a transaction ID is already associated with the snapshot.
Returns
Type Description
iterable of bytes a sequence of partition tokens

partition_read

partition_read(
    table,
    columns,
    keyset,
    index="",
    partition_size_bytes=None,
    max_partitions=None,
    *,
    retry=_MethodDefault._DEFAULT_VALUE,
    timeout=_MethodDefault._DEFAULT_VALUE
)

Perform a PartitionRead API request for rows in a table.

Parameters
Name Description
table str

name of the table from which to fetch data
columns list of str

names of columns to be retrieved
keyset KeySet

keys / ranges identifying rows to be retrieved
index str

(Optional) name of index to use, rather than the table's primary key
partition_size_bytes int

(Optional) desired size for each partition generated. The service uses this as a hint, the actual partition size may differ.
max_partitions int

(Optional) desired maximum number of partitions generated. The service uses this as a hint, the actual number of partitions may differ.
retry google.api_core.retry.Retry

(Optional) The retry settings for this request.
timeout float

(Optional) The timeout for this request.
Exceptions
Type Description
ValueError for single-use snapshots, or if a transaction ID is already associated with the snapshot.
Returns
Type Description
iterable of bytes a sequence of partition tokens

read

read(
    table,
    columns,
    keyset,
    index="",
    limit=0,
    partition=None,
    request_options=None,
    data_boost_enabled=False,
    directed_read_options=None,
    *,
    retry=_MethodDefault._DEFAULT_VALUE,
    timeout=_MethodDefault._DEFAULT_VALUE,
    column_info=None,
    lazy_decode=False
)

Perform a StreamingRead API request for rows in a table.

Parameters
Name Description
table str

name of the table from which to fetch data
columns list of str

names of columns to be retrieved
keyset KeySet

keys / ranges identifying rows to be retrieved
index str

(Optional) name of index to use, rather than the table's primary key
limit int

(Optional) maximum number of rows to return. Incompatible with partition.
partition bytes

(Optional) one of the partition tokens returned from partition_read. Incompatible with limit.
request_options RequestOptions

(Optional) Common options for this request. If a dict is provided, it must be of the same form as the protobuf message RequestOptions. Please note, the transactionTag setting will be ignored for snapshot as it's not supported for read-only transactions.
retry google.api_core.retry.Retry

(Optional) The retry settings for this request.
timeout float

(Optional) The timeout for this request.
directed_read_options DirectedReadOptions or dict

(Optional) Request level option used to set the directed_read_options for all ReadRequests and ExecuteSqlRequests that indicates which replicas or regions should be used for non-transactional reads or queries.
column_info dict

(Optional) dict of mapping between column names and additional column information. An object where column names as keys and custom objects as corresponding values for deserialization. It's specifically useful for data types like protobuf where deserialization logic is on user-specific code. When provided, the custom object enables deserialization of backend-received column data. If not provided, data remains serialized as bytes for Proto Messages and integer for Proto Enums.
lazy_decode bool

(Optional) If this argument is set to true, the iterator returns the underlying protobuf values instead of decoded Python objects. This reduces the time that is needed to iterate through large result sets. The application is responsible for decoding the data that is needed. The returned row iterator contains two functions that can be used for this. iterator.decode_row(row) decodes all the columns in the given row to an array of Python objects. iterator.decode_column(row, column_index) decodes one specific column in the given row.
Exceptions
Type Description
ValueError for reuse of single-use snapshots, or if a transaction ID is already pending for multiple-use snapshots.
Returns
Type Description
StreamedResultSet a result set instance which can be used to consume rows.