google.appengine.datastore.datastore_rpc.BaseConnection

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Datastore connection base class.

Inherits From: expected_type

google.appengine.datastore.datastore_rpc.BaseConnection(
    adapter=None, config=None, _api_version=_DATASTORE_V3
)

NOTE: Do not instantiate this class; use Connection or TransactionalConnection instead.

This is not a traditional database connection -- with App Engine, in the end the connection is always implicit in the process state. There is also no intent to be compatible with PEP 249 (Python's Database-API). But it is a useful abstraction to have an explicit object that manages the database interaction, and especially transactions. Other settings related to the App Engine datastore are also stored here (e.g. the RPC timeout).

A similar class in the Java API to the App Engine datastore is DatastoreServiceConfig (but in Java, transaction state is always held by the current thread).

To use transactions, call connection.new_transaction(). This returns a new connection (an instance of the TransactionalConnection subclass) which you should use for all operations in the transaction.

This model supports multiple unrelated concurrent transactions (but not nested transactions as this concept is commonly understood in the relational database world).

When the transaction is done, call .commit() or .rollback() on the transactional connection. If .commit() returns False, the transaction failed and none of your operations made it to the datastore; if it returns True, all your operations were committed. The transactional connection cannot be used once .commit() or .rollback() is called.

Transactions are created lazily. The first operation that requires a transaction handle will issue the low-level BeginTransaction request and wait for it to return.

Transactions keep track of the entity group. All operations within a transaction must use the same entity group. An entity group (currently) comprises an app id, a namespace, and a top-level key (a kind and an id or name). The first operation performed determines the entity group. There is some special-casing when the first operation is a put() of an entity with an incomplete key; in this case the entity group is determined after the operation returns.

NOTE: the datastore stubs in the dev_appserver currently support only a single concurrent transaction. Specifically, the (old) file stub locks up if an attempt is made to start a new transaction while a transaction is already in use, whereas the sqlite stub fails an assertion.

Methods

async_begin_transaction

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async_begin_transaction(
    config, app, previous_transaction=None, mode=TransactionMode.UNKNOWN
)

Asynchronous BeginTransaction operation.

async_delete

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async_delete(
    config, keys, extra_hook=None
)

Asynchronous Delete operation.

async_get

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async_get(
    config, keys, extra_hook=None
)

Asynchronous Get operation.

async_get_indexes

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async_get_indexes(
    config, extra_hook=None, _app=None
)

Asynchronous get indexes operation.

async_put

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async_put(
    config, entities, extra_hook=None
)

Asynchronous Put operation.

NOTE: If any of the entities has an incomplete key, this will not patch up those entities with the complete key.

begin_transaction

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begin_transaction(
    app, previous_transaction=None, mode=TransactionMode.UNKNOWN
)

Synchronous BeginTransaction operation.

NOTE: In most cases the new_transaction() method is preferred, since that returns a TransactionalConnection object which will begin the transaction lazily.

check_rpc_success

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check_rpc_success(
    rpc
)

Check for RPC success and translate exceptions.

This wraps rpc.check_success() and should be called instead of that.

This also removes the RPC from the list of pending RPCs, once it has completed.

create_rpc

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create_rpc(
    config=None, service_name=None
)

Create an RPC object using the configuration parameters.

Internal only.

NOTES:

(1) The RPC object returned can only be used to make a single call (for details see apiproxy_stub_map.UserRPC).

(2) To make a call, use one of the specific methods on the Connection object, such as conn.put(entities). This sends the call to the server but does not wait. To wait for the call to finish and get the result, call rpc.get_result().

delete

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delete(
    keys
)

Synchronous Delete operation.

get

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get(
    keys
)

Synchronous Get operation.

get_datastore_type

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get_datastore_type(
    app=None
)

Tries to get the datastore type for the given app.

This function is only guaranteed to return something other than UNKNOWN_DATASTORE when running in production and querying the current app.

get_indexes

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get_indexes()

Synchronous get indexes operation.

get_pending_rpcs

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get_pending_rpcs()

Return (a copy of) the list of currently pending RPCs.

is_pending

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is_pending(
    rpc
)

Check whether an RPC object is currently pending.

Note that 'pending' in this context refers to an RPC associated with this connection for which _remove_pending() hasn't been called yet; normally this is called by check_rpc_success() which itself is called by the various result hooks. A pending RPC may be in the RUNNING or FINISHING state.

If the argument is a MultiRpc object, this returns true if at least one of its wrapped RPCs is pending.

make_rpc_call

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make_rpc_call(
    config,
    method,
    request,
    response,
    get_result_hook=None,
    user_data=None,
    service_name=None
)

Make an RPC call.

Internal only.

Except for the added config argument, this is a thin wrapper around UserRPC.make_call().

put

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put(
    entities
)

Synchronous Put operation.

NOTE: If any of the entities has an incomplete key, this will not patch up those entities with the complete key.

wait_for_all_pending_rpcs

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wait_for_all_pending_rpcs()

Wait for all currently pending RPCs to complete.