Commit 99c87f14 authored by Michael Manfre's avatar Michael Manfre Committed by Anssi Kääriäinen
Browse files

Fixed #17671 - Cursors are now context managers.

parent 04a2a6b0

django/db/backends/__init__.py

+4 −1
Original line number Diff line number Diff line 
import datetime

import time



from django.db.utils import DatabaseError

from django.db.utils import DatabaseError, ProgrammingError



try:

    from django.utils.six.moves import _thread as thread
@@ -664,6 +664,9 @@ class BaseDatabaseFeatures(object): 
    # Does the backend require a connection reset after each material schema change?

    connection_persists_old_columns = False



    # What kind of error does the backend throw when accessing closed cursor?

    closed_cursor_error_class = ProgrammingError



    def __init__(self, connection):

        self.connection = connection

django/db/backends/postgresql_psycopg2/base.py

+2 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ from django.db.backends.postgresql_psycopg2.creation import DatabaseCreation 
from django.db.backends.postgresql_psycopg2.version import get_version

from django.db.backends.postgresql_psycopg2.introspection import DatabaseIntrospection

from django.db.backends.postgresql_psycopg2.schema import DatabaseSchemaEditor

from django.db.utils import InterfaceError

from django.utils.encoding import force_str

from django.utils.functional import cached_property

from django.utils.safestring import SafeText, SafeBytes
@@ -60,6 +61,7 @@ class DatabaseFeatures(BaseDatabaseFeatures): 
    can_rollback_ddl = True

    supports_combined_alters = True

    nulls_order_largest = True

    closed_cursor_error_class = InterfaceError





class DatabaseWrapper(BaseDatabaseWrapper):

django/db/backends/utils.py

+8 −0
Original line number Diff line number Diff line
@@ -36,6 +36,14 @@ class CursorWrapper(object): 
    def __iter__(self):

        return iter(self.cursor)



    def __enter__(self):

        return self



    def __exit__(self, type, value, traceback):

        # Ticket #17671 - Close instead of passing thru to avoid backend

        # specific behavior.

        self.close()





class CursorDebugWrapper(CursorWrapper):

docs/releases/1.7.txt

+19 −0
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@@ -111,6 +111,25 @@ In addition, the widgets now display a help message when the browser and 
server time zone are different, to clarify how the value inserted in the field

will be interpreted.



Using database cursors as context managers

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



Prior to Python 2.7, database cursors could be used as a context manager. The

specific backend's cursor defined the behavior of the context manager. The

behavior of magic method lookups was changed with Python 2.7 and cursors were

no longer usable as context managers.



Django 1.7 allows a cursor to be used as a context manager that is a shortcut

for the following, instead of backend specific behavior.



.. code-block:: python



    c = connection.cursor()

    try:

        c.execute(...)

    finally:

        c.close()



Minor features

~~~~~~~~~~~~~~

docs/topics/db/sql.txt

+27 −0
Original line number Diff line number Diff line
@@ -297,3 +297,30 @@ database library will automatically escape your parameters as necessary. 
Also note that Django expects the ``"%s"`` placeholder, *not* the ``"?"``

placeholder, which is used by the SQLite Python bindings. This is for the sake

of consistency and sanity.



.. versionchanged:: 1.7



:pep:`249` does not state whether a cursor should be usable as a context

manager. Prior to Python 2.7, a cursor was usable as a context manager due

an unexpected behavior in magic method lookups (`Python ticket #9220`_).

Django 1.7 explicitly added support to allow using a cursor as context

manager.



.. _`Python ticket #9220`: http://bugs.python.org/issue9220



Using a cursor as a context manager:



.. code-block:: python



    with connection.cursor() as c:

        c.execute(...)



is equivalent to:



.. code-block:: python



    c = connection.cursor()

    try:

        c.execute(...)

    finally:

        c.close()
 
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