Create / interact with Google Cloud Datastore transactions.
Classes
Transaction
Transaction
(
client
,
read_only
=
False
)
An abstraction representing datastore Transactions.
Transactions can be used to build up a bulk mutation and ensure all or none succeed (transactionally).
For example, the following snippet of code will put the two save
operations (either insert
or upsert
) into the same
mutation, and execute those within a transaction:
.. testsetup:: txn-put-multi, txn-api
import os
import uuid
from google.cloud import datastore
from tests.system.test_system import Config # system tests
unique = os.getenv('CIRCLE_BUILD_NUM', str(uuid.uuid4())[0:8])
client = datastore.Client(namespace='ns{}'.format(unique))
key1 = client.key('_Doctest')
entity1 = datastore.Entity(key=key1)
entity1['foo'] = 1337
key2 = client.key('_Doctest', 'abcd1234')
entity2 = datastore.Entity(key=key2)
entity2['foo'] = 42
Config.TO_DELETE.extend([entity1, entity2])
.. doctest:: txn-put-multi
>>> with client.transaction():
... client.put_multi([entity1, entity2])
Because it derives from xref_Batch, Transaction
also provides put
and delete
methods:
.. doctest:: txn-api
with client.transaction() as xact: ... xact.put(entity1) ... xact.delete(entity2.key)
By default, the transaction is rolled back if the transaction block exits with an error:
.. testsetup:: txn-error
import os
import uuid
from google.cloud import datastore
unique = os.getenv('CIRCLE_BUILD_NUM', str(uuid.uuid4())[0:8])
client = datastore.Client(namespace='ns{}'.format(unique))
def do_some_work():
return
class SomeException(Exception):
pass
.. doctest:: txn-error
>>> with client.transaction():
... do_some_work()
... raise SomeException # rolls back
Traceback (most recent call last):
...
SomeException
If the transaction block exits without an exception, it will commit by default.
.. warning::
Inside a transaction, automatically assigned IDs for
entities will not be available at save time! That means, if you
try:
.. testsetup:: txn-entity-key, txn-entity-key-after, txn-manual
import os
import uuid
from google.cloud import datastore
from tests.system.test_system import Config # system tests
unique = os.getenv('CIRCLE_BUILD_NUM', str(uuid.uuid4())[0:8])
client = datastore.Client(namespace='ns{}'.format(unique))
def Entity(*args, **kwargs):
entity = datastore.Entity(*args, **kwargs)
Config.TO_DELETE.append(entity)
return entity
.. doctest:: txn-entity-key
>>> with client.transaction():
... entity = Entity(key=client.key('Thing'))
... client.put(entity)
entity
won't have a complete key until the transaction is
committed.
Once you exit the transaction (or call commit
), the
automatically generated ID will be assigned to the entity:
.. doctest:: txn-entity-key-after
>>> with client.transaction():
... entity = Entity(key=client.key('Thing'))
... client.put(entity)
... print(entity.key.is_partial) # There is no ID on this key.
...
True
>>> print(entity.key.is_partial) # There *is* an ID.
False
If you don't want to use the context manager you can initialize a transaction manually:
.. doctest:: txn-manual
transaction = client.transaction() transaction.begin()
entity = Entity(key=client.key('Thing')) transaction.put(entity)
transaction.commit()
| Name | Description |
| client | Client
the client used to connect to datastore. |
| read_only | bool
indicates the transaction is read only. |
