Notice: Over the next few months, we're reorganizing the App Engine documentation site to make it easier to find content and better align with the rest of Google Cloud products. The same content will be available, but the navigation will now match the rest of the Cloud products.

Python 3.10 is now available in preview.

google.appengine.datastore.datastore_rpc.BaseConnection

Datastore connection base class.

Inherits From: expected_type

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.

adapter Optional AbstractAdapter subclass instance; default IdentityAdapter.
config Optional Configuration object.

adapter The adapter used by this connection.
config The default configuration used by this connection.

Methods

async_begin_transaction

View source

Asynchronous BeginTransaction operation.

Args
config A configuration object or None. Defaults are taken from the connection's default configuration.
app Application ID.
previous_transaction The transaction to reset.
mode The transaction mode.

Returns
A MultiRpc object.

async_delete

View source

Asynchronous Delete operation.

Args
config A Configuration object or None. Defaults are taken from the connection's default configuration.
keys An iterable of user-level key objects.
extra_hook Optional function to be called once the RPC has completed.

Returns
A MultiRpc object.

async_get

View source

Asynchronous Get operation.

Args
config A Configuration object or None. Defaults are taken from the connection's default configuration.
keys An iterable of user-level key objects.
extra_hook Optional function to be called on the result once the RPC has completed.

Returns
A MultiRpc object.

async_get_indexes

View source

Asynchronous get indexes operation.

Args
config A Configuration object or None. Defaults are taken from the connection's default configuration.
extra_hook Optional function to be called once the RPC has completed.

Returns
A MultiRpc object.

async_put

View source

Asynchronous Put operation.

Args
config: A Configuration object or None. Defaults are taken from the connection's default configuration. entities: An iterable of user-level entity objects. extra_hook: Optional function to be called on the result once the RPC has completed.
Returns A MultiRpc object.

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

begin_transaction

View source

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.

Args
app Application ID.
previous_transaction The transaction to reset.
mode The transaction mode.

Returns
An object representing a transaction or None.

check_rpc_success

View source

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.

Args
rpc A UserRPC or MultiRpc object.

Raises
Nothing if the call succeeded; various datastore_errors.Error subclasses if ApplicationError was raised by rpc.check_success().

create_rpc

View source

Create an RPC object using the configuration parameters.

Internal only.

Args
config Optional Configuration object.
service_name Optional datastore service name.

Returns
A new UserRPC object with the designated settings.

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

View source

Synchronous Delete operation.

Args
keys An iterable of user-level key objects.

Returns
None.

get

View source

Synchronous Get operation.

Args
keys An iterable of user-level key objects.

Returns
A list of user-level entity objects and None values, corresponding 1:1 to the argument keys. A None means there is no entity for the corresponding key.

get_datastore_type

View source

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

View source

Synchronous get indexes operation.

Returns
user-level indexes representation

get_pending_rpcs

View source

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

is_pending

View source

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

View source

Make an RPC call.

Internal only.

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

Args
config A Configuration object or None. Defaults are taken from the connection's default configuration.
method The method name.
request The request protocol buffer.
response The response protocol buffer.
get_result_hook Optional get-result hook function. If not None, this must be a function with exactly one argument, the RPC object (self). Its return value is returned from get_result().
user_data Optional additional arbitrary data for the get-result hook function. This can be accessed as rpc.user_data. The type of this value is up to the service module.

Returns
The UserRPC object used for the call.

put

View source

Synchronous Put operation.

Args
entities An iterable of user-level entity objects.

Returns
A list of user-level key objects, corresponding 1:1 to the argument entities.

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

View source

Wait for all currently pending RPCs to complete.

DEFAULT_MAX_ENTITY_GROUPS_PER_RPC 10
HIGH_REPLICATION_DATASTORE 2
MAX_ALLOCATE_IDS_KEYS 500
MAX_DELETE_KEYS 500
MAX_GET_KEYS 1000
MAX_PUT_ENTITIES 500
MAX_RPC_BYTES 1048576
UNKNOWN_DATASTORE 0