Fixed #28853 -- Updated connection.cursor() uses to use a context manager.

11 files changed, 155 insertions, 180 deletions

diff --git a/django/contrib/gis/db/backends/mysql/introspection.py b/django/contrib/gis/db/backends/mysql/introspection.py
index 364cdeecfe..ba125ec4af 100644
--- a/django/contrib/gis/db/backends/mysql/introspection.py
+++ b/django/contrib/gis/db/backends/mysql/introspection.py
@@ -11,8 +11,7 @@ class MySQLIntrospection(DatabaseIntrospection):
     data_types_reverse[FIELD_TYPE.GEOMETRY] = 'GeometryField'
 
     def get_geometry_type(self, table_name, geo_col):
-        cursor = self.connection.cursor()
-        try:
+        with self.connection.cursor() as cursor:
             # In order to get the specific geometry type of the field,
             # we introspect on the table definition using `DESCRIBE`.
             cursor.execute('DESCRIBE %s' %
@@ -27,9 +26,6 @@ class MySQLIntrospection(DatabaseIntrospection):
                     field_type = OGRGeomType(typ).django
                     field_params = {}
                     break
-        finally:
-            cursor.close()
-
         return field_type, field_params
 
     def supports_spatial_index(self, cursor, table_name):
diff --git a/django/contrib/gis/db/backends/oracle/introspection.py b/django/contrib/gis/db/backends/oracle/introspection.py
index 446dc78216..7f4f886a34 100644
--- a/django/contrib/gis/db/backends/oracle/introspection.py
+++ b/django/contrib/gis/db/backends/oracle/introspection.py
@@ -11,8 +11,7 @@ class OracleIntrospection(DatabaseIntrospection):
     data_types_reverse[cx_Oracle.OBJECT] = 'GeometryField'
 
     def get_geometry_type(self, table_name, geo_col):
-        cursor = self.connection.cursor()
-        try:
+        with self.connection.cursor() as cursor:
             # Querying USER_SDO_GEOM_METADATA to get the SRID and dimension information.
             try:
                 cursor.execute(
@@ -40,7 +39,4 @@ class OracleIntrospection(DatabaseIntrospection):
             dim = dim.size()
             if dim != 2:
                 field_params['dim'] = dim
-        finally:
-            cursor.close()
-
         return field_type, field_params
diff --git a/django/contrib/gis/db/backends/postgis/introspection.py b/django/contrib/gis/db/backends/postgis/introspection.py
index 3a90ebf5c5..97fa7480e6 100644
--- a/django/contrib/gis/db/backends/postgis/introspection.py
+++ b/django/contrib/gis/db/backends/postgis/introspection.py
@@ -59,15 +59,11 @@ class PostGISIntrospection(DatabaseIntrospection):
         # to query the PostgreSQL pg_type table corresponding to the
         # PostGIS custom data types.
         oid_sql = 'SELECT "oid" FROM "pg_type" WHERE "typname" = %s'
-        cursor = self.connection.cursor()
-        try:
+        with self.connection.cursor() as cursor:
             for field_type in field_types:
                 cursor.execute(oid_sql, (field_type[0],))
                 for result in cursor.fetchall():
                     postgis_types[result[0]] = field_type[1]
-        finally:
-            cursor.close()
-
         return postgis_types
 
     def get_field_type(self, data_type, description):
@@ -88,8 +84,7 @@ class PostGISIntrospection(DatabaseIntrospection):
         PointField or a PolygonField).  Thus, this routine queries the PostGIS
         metadata tables to determine the geometry type.
         """
-        cursor = self.connection.cursor()
-        try:
+        with self.connection.cursor() as cursor:
             try:
                 # First seeing if this geometry column is in the `geometry_columns`
                 cursor.execute('SELECT "coord_dimension", "srid", "type" '
@@ -122,7 +117,4 @@ class PostGISIntrospection(DatabaseIntrospection):
                 field_params['srid'] = srid
             if dim != 2:
                 field_params['dim'] = dim
-        finally:
-            cursor.close()
-
         return field_type, field_params
diff --git a/django/contrib/gis/db/backends/spatialite/introspection.py b/django/contrib/gis/db/backends/spatialite/introspection.py
index 98fda427d0..5cd5613b69 100644
--- a/django/contrib/gis/db/backends/spatialite/introspection.py
+++ b/django/contrib/gis/db/backends/spatialite/introspection.py
@@ -25,8 +25,7 @@ class SpatiaLiteIntrospection(DatabaseIntrospection):
     data_types_reverse = GeoFlexibleFieldLookupDict()
 
     def get_geometry_type(self, table_name, geo_col):
-        cursor = self.connection.cursor()
-        try:
+        with self.connection.cursor() as cursor:
             # Querying the `geometry_columns` table to get additional metadata.
             cursor.execute('SELECT coord_dimension, srid, geometry_type '
                            'FROM geometry_columns '
@@ -55,9 +54,6 @@ class SpatiaLiteIntrospection(DatabaseIntrospection):
                 field_params['srid'] = srid
             if (isinstance(dim, str) and 'Z' in dim) or dim == 3:
                 field_params['dim'] = 3
-        finally:
-            cursor.close()
-
         return field_type, field_params
 
     def get_constraints(self, cursor, table_name):
diff --git a/django/db/backends/base/base.py b/django/db/backends/base/base.py
index 468eb16e14..53c3c30063 100644
--- a/django/db/backends/base/base.py
+++ b/django/db/backends/base/base.py
@@ -573,11 +573,10 @@ class BaseDatabaseWrapper:
         Provide a cursor: with self.temporary_connection() as cursor: ...
         """
         must_close = self.connection is None
-        cursor = self.cursor()
         try:
-            yield cursor
+            with self.cursor() as cursor:
+                yield cursor
         finally:
-            cursor.close()
             if must_close:
                 self.close()
 
diff --git a/django/db/backends/base/introspection.py b/django/db/backends/base/introspection.py
index 154ae22bf1..8fe8966a21 100644
--- a/django/db/backends/base/introspection.py
+++ b/django/db/backends/base/introspection.py
@@ -116,21 +116,20 @@ class BaseDatabaseIntrospection:
         from django.db import router
 
         sequence_list = []
-        cursor = self.connection.cursor()
-
-        for app_config in apps.get_app_configs():
-            for model in router.get_migratable_models(app_config, self.connection.alias):
-                if not model._meta.managed:
-                    continue
-                if model._meta.swapped:
-                    continue
-                sequence_list.extend(self.get_sequences(cursor, model._meta.db_table, model._meta.local_fields))
-                for f in model._meta.local_many_to_many:
-                    # If this is an m2m using an intermediate table,
-                    # we don't need to reset the sequence.
-                    if f.remote_field.through is None:
-                        sequence = self.get_sequences(cursor, f.m2m_db_table())
-                        sequence_list.extend(sequence or [{'table': f.m2m_db_table(), 'column': None}])
+        with self.connection.cursor() as cursor:
+            for app_config in apps.get_app_configs():
+                for model in router.get_migratable_models(app_config, self.connection.alias):
+                    if not model._meta.managed:
+                        continue
+                    if model._meta.swapped:
+                        continue
+                    sequence_list.extend(self.get_sequences(cursor, model._meta.db_table, model._meta.local_fields))
+                    for f in model._meta.local_many_to_many:
+                        # If this is an m2m using an intermediate table,
+                        # we don't need to reset the sequence.
+                        if f.remote_field.through is None:
+                            sequence = self.get_sequences(cursor, f.m2m_db_table())
+                            sequence_list.extend(sequence or [{'table': f.m2m_db_table(), 'column': None}])
         return sequence_list
 
     def get_sequences(self, cursor, table_name, table_fields=()):
diff --git a/django/db/backends/mysql/base.py b/django/db/backends/mysql/base.py
index abf8f55736..6b82afc45d 100644
--- a/django/db/backends/mysql/base.py
+++ b/django/db/backends/mysql/base.py
@@ -294,36 +294,37 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         Backends can override this method if they can more directly apply
         constraint checking (e.g. via "SET CONSTRAINTS ALL IMMEDIATE")
         """
-        cursor = self.cursor()
-        if table_names is None:
-            table_names = self.introspection.table_names(cursor)
-        for table_name in table_names:
-            primary_key_column_name = self.introspection.get_primary_key_column(cursor, table_name)
-            if not primary_key_column_name:
-                continue
-            key_columns = self.introspection.get_key_columns(cursor, table_name)
-            for column_name, referenced_table_name, referenced_column_name in key_columns:
-                cursor.execute(
-                    """
-                    SELECT REFERRING.`%s`, REFERRING.`%s` FROM `%s` as REFERRING
-                    LEFT JOIN `%s` as REFERRED
-                    ON (REFERRING.`%s` = REFERRED.`%s`)
-                    WHERE REFERRING.`%s` IS NOT NULL AND REFERRED.`%s` IS NULL
-                    """ % (
-                        primary_key_column_name, column_name, table_name,
-                        referenced_table_name, column_name, referenced_column_name,
-                        column_name, referenced_column_name,
-                    )
-                )
-                for bad_row in cursor.fetchall():
-                    raise utils.IntegrityError(
-                        "The row in table '%s' with primary key '%s' has an invalid "
-                        "foreign key: %s.%s contains a value '%s' that does not have a corresponding value in %s.%s."
-                        % (
-                            table_name, bad_row[0], table_name, column_name,
-                            bad_row[1], referenced_table_name, referenced_column_name,
+        with self.cursor() as cursor:
+            if table_names is None:
+                table_names = self.introspection.table_names(cursor)
+            for table_name in table_names:
+                primary_key_column_name = self.introspection.get_primary_key_column(cursor, table_name)
+                if not primary_key_column_name:
+                    continue
+                key_columns = self.introspection.get_key_columns(cursor, table_name)
+                for column_name, referenced_table_name, referenced_column_name in key_columns:
+                    cursor.execute(
+                        """
+                        SELECT REFERRING.`%s`, REFERRING.`%s` FROM `%s` as REFERRING
+                        LEFT JOIN `%s` as REFERRED
+                        ON (REFERRING.`%s` = REFERRED.`%s`)
+                        WHERE REFERRING.`%s` IS NOT NULL AND REFERRED.`%s` IS NULL
+                        """ % (
+                            primary_key_column_name, column_name, table_name,
+                            referenced_table_name, column_name, referenced_column_name,
+                            column_name, referenced_column_name,
                         )
                     )
+                    for bad_row in cursor.fetchall():
+                        raise utils.IntegrityError(
+                            "The row in table '%s' with primary key '%s' has an invalid "
+                            "foreign key: %s.%s contains a value '%s' that does not "
+                            "have a corresponding value in %s.%s."
+                            % (
+                                table_name, bad_row[0], table_name, column_name,
+                                bad_row[1], referenced_table_name, referenced_column_name,
+                            )
+                        )
 
     def is_usable(self):
         try:
diff --git a/django/db/backends/oracle/creation.py b/django/db/backends/oracle/creation.py
index fe053c54f7..aa57e6a6ab 100644
--- a/django/db/backends/oracle/creation.py
+++ b/django/db/backends/oracle/creation.py
@@ -30,75 +30,72 @@ class DatabaseCreation(BaseDatabaseCreation):
 
     def _create_test_db(self, verbosity=1, autoclobber=False, keepdb=False):
         parameters = self._get_test_db_params()
-        cursor = self._maindb_connection.cursor()
-        if self._test_database_create():
-            try:
-                self._execute_test_db_creation(cursor, parameters, verbosity, keepdb)
-            except Exception as e:
-                if 'ORA-01543' not in str(e):
-                    # All errors except "tablespace already exists" cancel tests
-                    sys.stderr.write("Got an error creating the test database: %s\n" % e)
-                    sys.exit(2)
-                if not autoclobber:
-                    confirm = input(
-                        "It appears the test database, %s, already exists. "
-                        "Type 'yes' to delete it, or 'no' to cancel: " % parameters['user'])
-                if autoclobber or confirm == 'yes':
-                    if verbosity >= 1:
-                        print("Destroying old test database for alias '%s'..." % self.connection.alias)
-                    try:
-                        self._execute_test_db_destruction(cursor, parameters, verbosity)
-                    except DatabaseError as e:
-                        if 'ORA-29857' in str(e):
-                            self._handle_objects_preventing_db_destruction(cursor, parameters,
-                                                                           verbosity, autoclobber)
-                        else:
-                            # Ran into a database error that isn't about leftover objects in the tablespace
+        with self._maindb_connection.cursor() as cursor:
+            if self._test_database_create():
+                try:
+                    self._execute_test_db_creation(cursor, parameters, verbosity, keepdb)
+                except Exception as e:
+                    if 'ORA-01543' not in str(e):
+                        # All errors except "tablespace already exists" cancel tests
+                        sys.stderr.write("Got an error creating the test database: %s\n" % e)
+                        sys.exit(2)
+                    if not autoclobber:
+                        confirm = input(
+                            "It appears the test database, %s, already exists. "
+                            "Type 'yes' to delete it, or 'no' to cancel: " % parameters['user'])
+                    if autoclobber or confirm == 'yes':
+                        if verbosity >= 1:
+                            print("Destroying old test database for alias '%s'..." % self.connection.alias)
+                        try:
+                            self._execute_test_db_destruction(cursor, parameters, verbosity)
+                        except DatabaseError as e:
+                            if 'ORA-29857' in str(e):
+                                self._handle_objects_preventing_db_destruction(cursor, parameters,
+                                                                               verbosity, autoclobber)
+                            else:
+                                # Ran into a database error that isn't about leftover objects in the tablespace
+                                sys.stderr.write("Got an error destroying the old test database: %s\n" % e)
+                                sys.exit(2)
+                        except Exception as e:
                             sys.stderr.write("Got an error destroying the old test database: %s\n" % e)
                             sys.exit(2)
-                    except Exception as e:
-                        sys.stderr.write("Got an error destroying the old test database: %s\n" % e)
-                        sys.exit(2)
-                    try:
-                        self._execute_test_db_creation(cursor, parameters, verbosity, keepdb)
-                    except Exception as e:
-                        sys.stderr.write("Got an error recreating the test database: %s\n" % e)
-                        sys.exit(2)
-                else:
-                    print("Tests cancelled.")
-                    sys.exit(1)
+                        try:
+                            self._execute_test_db_creation(cursor, parameters, verbosity, keepdb)
+                        except Exception as e:
+                            sys.stderr.write("Got an error recreating the test database: %s\n" % e)
+                            sys.exit(2)
+                    else:
+                        print("Tests cancelled.")
+                        sys.exit(1)
 
-        if self._test_user_create():
-            if verbosity >= 1:
-                print("Creating test user...")
-            try:
-                self._create_test_user(cursor, parameters, verbosity, keepdb)
-            except Exception as e:
-                if 'ORA-01920' not in str(e):
-                    # All errors except "user already exists" cancel tests
-                    sys.stderr.write("Got an error creating the test user: %s\n" % e)
-                    sys.exit(2)
-                if not autoclobber:
-                    confirm = input(
-                        "It appears the test user, %s, already exists. Type "
-                        "'yes' to delete it, or 'no' to cancel: " % parameters['user'])
-                if autoclobber or confirm == 'yes':
-                    try:
-                        if verbosity >= 1:
-                            print("Destroying old test user...")
-                        self._destroy_test_user(cursor, parameters, verbosity)
-                        if verbosity >= 1:
-                            print("Creating test user...")
-                        self._create_test_user(cursor, parameters, verbosity, keepdb)
-                    except Exception as e:
-                        sys.stderr.write("Got an error recreating the test user: %s\n" % e)
+            if self._test_user_create():
+                if verbosity >= 1:
+                    print("Creating test user...")
+                try:
+                    self._create_test_user(cursor, parameters, verbosity, keepdb)
+                except Exception as e:
+                    if 'ORA-01920' not in str(e):
+                        # All errors except "user already exists" cancel tests
+                        sys.stderr.write("Got an error creating the test user: %s\n" % e)
                         sys.exit(2)
-                else:
-                    print("Tests cancelled.")
-                    sys.exit(1)
-
-        # Cursor must be closed before closing connection.
-        cursor.close()
+                    if not autoclobber:
+                        confirm = input(
+                            "It appears the test user, %s, already exists. Type "
+                            "'yes' to delete it, or 'no' to cancel: " % parameters['user'])
+                    if autoclobber or confirm == 'yes':
+                        try:
+                            if verbosity >= 1:
+                                print("Destroying old test user...")
+                            self._destroy_test_user(cursor, parameters, verbosity)
+                            if verbosity >= 1:
+                                print("Creating test user...")
+                            self._create_test_user(cursor, parameters, verbosity, keepdb)
+                        except Exception as e:
+                            sys.stderr.write("Got an error recreating the test user: %s\n" % e)
+                            sys.exit(2)
+                    else:
+                        print("Tests cancelled.")
+                        sys.exit(1)
         self._maindb_connection.close()  # done with main user -- test user and tablespaces created
         self._switch_to_test_user(parameters)
         return self.connection.settings_dict['NAME']
@@ -175,17 +172,15 @@ class DatabaseCreation(BaseDatabaseCreation):
         self.connection.settings_dict['PASSWORD'] = self.connection.settings_dict['SAVED_PASSWORD']
         self.connection.close()
         parameters = self._get_test_db_params()
-        cursor = self._maindb_connection.cursor()
-        if self._test_user_create():
-            if verbosity >= 1:
-                print('Destroying test user...')
-            self._destroy_test_user(cursor, parameters, verbosity)
-        if self._test_database_create():
-            if verbosity >= 1:
-                print('Destroying test database tables...')
-            self._execute_test_db_destruction(cursor, parameters, verbosity)
-        # Cursor must be closed before closing connection.
-        cursor.close()
+        with self._maindb_connection.cursor() as cursor:
+            if self._test_user_create():
+                if verbosity >= 1:
+                    print('Destroying test user...')
+                self._destroy_test_user(cursor, parameters, verbosity)
+            if self._test_database_create():
+                if verbosity >= 1:
+                    print('Destroying test database tables...')
+                self._execute_test_db_destruction(cursor, parameters, verbosity)
         self._maindb_connection.close()
 
     def _execute_test_db_creation(self, cursor, parameters, verbosity, keepdb=False):
diff --git a/django/db/backends/sqlite3/base.py b/django/db/backends/sqlite3/base.py
index 40b205cf30..13f9a575e2 100644
--- a/django/db/backends/sqlite3/base.py
+++ b/django/db/backends/sqlite3/base.py
@@ -237,37 +237,37 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         Backends can override this method if they can more directly apply
         constraint checking (e.g. via "SET CONSTRAINTS ALL IMMEDIATE")
         """
-        cursor = self.cursor()
-        if table_names is None:
-            table_names = self.introspection.table_names(cursor)
-        for table_name in table_names:
-            primary_key_column_name = self.introspection.get_primary_key_column(cursor, table_name)
-            if not primary_key_column_name:
-                continue
-            key_columns = self.introspection.get_key_columns(cursor, table_name)
-            for column_name, referenced_table_name, referenced_column_name in key_columns:
-                cursor.execute(
-                    """
-                    SELECT REFERRING.`%s`, REFERRING.`%s` FROM `%s` as REFERRING
-                    LEFT JOIN `%s` as REFERRED
-                    ON (REFERRING.`%s` = REFERRED.`%s`)
-                    WHERE REFERRING.`%s` IS NOT NULL AND REFERRED.`%s` IS NULL
-                    """
-                    % (
-                        primary_key_column_name, column_name, table_name,
-                        referenced_table_name, column_name, referenced_column_name,
-                        column_name, referenced_column_name,
-                    )
-                )
-                for bad_row in cursor.fetchall():
-                    raise utils.IntegrityError(
-                        "The row in table '%s' with primary key '%s' has an "
-                        "invalid foreign key: %s.%s contains a value '%s' that "
-                        "does not have a corresponding value in %s.%s." % (
-                            table_name, bad_row[0], table_name, column_name,
-                            bad_row[1], referenced_table_name, referenced_column_name,
+        with self.cursor() as cursor:
+            if table_names is None:
+                table_names = self.introspection.table_names(cursor)
+            for table_name in table_names:
+                primary_key_column_name = self.introspection.get_primary_key_column(cursor, table_name)
+                if not primary_key_column_name:
+                    continue
+                key_columns = self.introspection.get_key_columns(cursor, table_name)
+                for column_name, referenced_table_name, referenced_column_name in key_columns:
+                    cursor.execute(
+                        """
+                        SELECT REFERRING.`%s`, REFERRING.`%s` FROM `%s` as REFERRING
+                        LEFT JOIN `%s` as REFERRED
+                        ON (REFERRING.`%s` = REFERRED.`%s`)
+                        WHERE REFERRING.`%s` IS NOT NULL AND REFERRED.`%s` IS NULL
+                        """
+                        % (
+                            primary_key_column_name, column_name, table_name,
+                            referenced_table_name, column_name, referenced_column_name,
+                            column_name, referenced_column_name,
                         )
                     )
+                    for bad_row in cursor.fetchall():
+                        raise utils.IntegrityError(
+                            "The row in table '%s' with primary key '%s' has an "
+                            "invalid foreign key: %s.%s contains a value '%s' that "
+                            "does not have a corresponding value in %s.%s." % (
+                                table_name, bad_row[0], table_name, column_name,
+                                bad_row[1], referenced_table_name, referenced_column_name,
+                            )
+                        )
 
     def is_usable(self):
         return True
diff --git a/django/db/migrations/executor.py b/django/db/migrations/executor.py
index ea7bc70db3..ebaf75634b 100644
--- a/django/db/migrations/executor.py
+++ b/django/db/migrations/executor.py
@@ -322,7 +322,8 @@ class MigrationExecutor:
         apps = after_state.apps
         found_create_model_migration = False
         found_add_field_migration = False
-        existing_table_names = self.connection.introspection.table_names(self.connection.cursor())
+        with self.connection.cursor() as cursor:
+            existing_table_names = self.connection.introspection.table_names(cursor)
         # Make sure all create model and add field operations are done
         for operation in migration.operations:
             if isinstance(operation, migrations.CreateModel):
diff --git a/django/test/testcases.py b/django/test/testcases.py
index afab58f2dc..4c32c87da5 100644
--- a/django/test/testcases.py
+++ b/django/test/testcases.py
@@ -852,9 +852,9 @@ class TransactionTestCase(SimpleTestCase):
                 no_style(), conn.introspection.sequence_list())
             if sql_list:
                 with transaction.atomic(using=db_name):
-                    cursor = conn.cursor()
-                    for sql in sql_list:
-                        cursor.execute(sql)
+                    with conn.cursor() as cursor:
+                        for sql in sql_list:
+                            cursor.execute(sql)
 
     def _fixture_setup(self):
         for db_name in self._databases_names(include_mirrors=False):