Class BatchSnapshot (1.13.0)

BatchSnapshot(database, read_timestamp=None, exact_staleness=None)

Wrapper for generating and processing read / query batches.

Parameters
Name	Description
`database`	`Database` database to use
`read_timestamp`	`datetime.datetime` Execute all reads at the given timestamp.
`exact_staleness`	`datetime.timedelta` Execute all reads at a timestamp that is `exact_staleness` old.

Methods

close

close()

Clean up underlying session.

execute_sql

execute_sql(*args, **kw)

Convenience method: perform query operation via snapshot.

See execute_sql.

from_dict

from_dict(database, mapping)

Reconstruct an instance from a mapping.

Parameters
Name	Description
`database`	`Database` database to use
`mapping`	`mapping` serialized state of the instance

generate_query_batches

generate_query_batches(
    sql, params=None, param_types=None, partition_size_bytes=None, max_partitions=None
)

Start a partitioned query operation.

Uses the PartitionQuery API request to start a partitioned query operation. Returns a list of batch information needed to peform the actual queries.

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.

Returns
Type	Description
`iterable of dict`	mappings of information used peform actual partitioned reads via `process_read_batch`.

generate_read_batches

generate_read_batches(
    table, columns, keyset, index="", partition_size_bytes=None, max_partitions=None
)

Start a partitioned batch read operation.

Uses the PartitionRead API request to initiate the partitioned read. Returns a list of batch information needed to perform the actual reads.

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.

Returns
Type	Description
`iterable of dict`	mappings of information used peform actual partitioned reads via `process_read_batch`.

process

process(batch)

Process a single, partitioned query or read.

Parameter
Name	Description
`batch`	`mapping` one of the mappings returned from an earlier call to `generate_query_batches`.

Exceptions
Type	Description
`ValueError`	if batch does not contain either 'read' or 'query'

Returns
Type	Description
`StreamedResultSet`	a result set instance which can be used to consume rows.

process_query_batch

process_query_batch(batch)

Process a single, partitioned query.

Parameter
Name	Description
`batch`	`mapping` one of the mappings returned from an earlier call to `generate_query_batches`.

Returns
Type	Description
`StreamedResultSet`	a result set instance which can be used to consume rows.

process_read_batch

process_read_batch(batch)

Process a single, partitioned read.

Parameter
Name	Description
`batch`	`mapping` one of the mappings returned from an earlier call to `generate_read_batches`.

Returns
Type	Description
`StreamedResultSet`	a result set instance which can be used to consume rows.

read

read(*args, **kw)

Convenience method: perform read operation via snapshot.

See read.

to_dict

to_dict()

Return state as a dictionary.

Result can be used to serialize the instance and reconstitute it later using from_dict.