103 lines
3.3 KiB
Python
103 lines
3.3 KiB
Python
"""
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15. Transactions
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Django handles transactions in three different ways. The default is to commit
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each transaction upon a write, but you can decorate a function to get
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commit-on-success behavior. Alternatively, you can manage the transaction
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manually.
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"""
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from django.db import models
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class Reporter(models.Model):
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first_name = models.CharField(max_length=30)
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last_name = models.CharField(max_length=30)
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email = models.EmailField()
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class Meta:
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ordering = ('first_name', 'last_name')
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def __unicode__(self):
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return u"%s %s" % (self.first_name, self.last_name)
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__test__ = {'API_TESTS':"""
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>>> from django.db import connection, transaction
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"""}
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from django.conf import settings
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building_docs = getattr(settings, 'BUILDING_DOCS', False)
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if building_docs or settings.DATABASE_ENGINE != 'mysql':
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__test__['API_TESTS'] += """
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# the default behavior is to autocommit after each save() action
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>>> def create_a_reporter_then_fail(first, last):
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... a = Reporter(first_name=first, last_name=last)
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... a.save()
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... raise Exception("I meant to do that")
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...
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>>> create_a_reporter_then_fail("Alice", "Smith")
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Traceback (most recent call last):
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...
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Exception: I meant to do that
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# The object created before the exception still exists
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>>> Reporter.objects.all()
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[<Reporter: Alice Smith>]
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# the autocommit decorator works exactly the same as the default behavior
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>>> autocomitted_create_then_fail = transaction.autocommit(create_a_reporter_then_fail)
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>>> autocomitted_create_then_fail("Ben", "Jones")
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Traceback (most recent call last):
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...
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Exception: I meant to do that
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# Same behavior as before
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>>> Reporter.objects.all()
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[<Reporter: Alice Smith>, <Reporter: Ben Jones>]
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# With the commit_on_success decorator, the transaction is only comitted if the
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# function doesn't throw an exception
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>>> committed_on_success = transaction.commit_on_success(create_a_reporter_then_fail)
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>>> committed_on_success("Carol", "Doe")
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Traceback (most recent call last):
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...
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Exception: I meant to do that
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# This time the object never got saved
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>>> Reporter.objects.all()
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[<Reporter: Alice Smith>, <Reporter: Ben Jones>]
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# If there aren't any exceptions, the data will get saved
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>>> def remove_a_reporter():
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... r = Reporter.objects.get(first_name="Alice")
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... r.delete()
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...
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>>> remove_comitted_on_success = transaction.commit_on_success(remove_a_reporter)
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>>> remove_comitted_on_success()
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>>> Reporter.objects.all()
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[<Reporter: Ben Jones>]
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# You can manually manage transactions if you really want to, but you
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# have to remember to commit/rollback
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>>> def manually_managed():
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... r = Reporter(first_name="Carol", last_name="Doe")
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... r.save()
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... transaction.commit()
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>>> manually_managed = transaction.commit_manually(manually_managed)
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>>> manually_managed()
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>>> Reporter.objects.all()
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[<Reporter: Ben Jones>, <Reporter: Carol Doe>]
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# If you forget, you'll get bad errors
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>>> def manually_managed_mistake():
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... r = Reporter(first_name="David", last_name="Davidson")
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... r.save()
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... # oops, I forgot to commit/rollback!
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>>> manually_managed_mistake = transaction.commit_manually(manually_managed_mistake)
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>>> manually_managed_mistake()
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Traceback (most recent call last):
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...
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TransactionManagementError: Transaction managed block ended with pending COMMIT/ROLLBACK
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"""
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