Fixed #19274 -- Made db connection creation overridable in subclasses

Connection creation was done in db backend ._cursor() call. This
included taking a new connection if needed, initializing the session
state for the new connection and finally creating the connection.

To allow easier modifying of these steps in subclasses (for example to
support connection pools) the _cursor() now calls get_new_connection()
and init_connection_state() if there isn't an existing connection. This
was done for all non-gis core backends. In addition the parameters used
for taking a connection are now created by get_connection_params().

We should also do the same for gis backends and encourage 3rd party
backends to use the same pattern. The pattern is not enforced in code,
and as the backends are private API this will not be required by
documentation either.

1 files changed, 69 insertions, 57 deletions

diff --git a/django/db/backends/oracle/base.py b/django/db/backends/oracle/base.py
index dfdfd4fd49..c6f072df3b 100644
--- a/django/db/backends/oracle/base.py
+++ b/django/db/backends/oracle/base.py
@@ -489,66 +489,78 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         return "%s/%s@%s" % (settings_dict['USER'],
                              settings_dict['PASSWORD'], dsn)
 
+    def create_cursor(self, conn):
+        return FormatStylePlaceholderCursor(conn)
+
+    def get_connection_params(self):
+        conn_params = self.settings_dict['OPTIONS'].copy()
+        if 'use_returning_into' in conn_params:
+            del conn_params['use_returning_into']
+        return conn_params
+
+    def get_new_connection(self, conn_params):
+        conn_string = convert_unicode(self._connect_string())
+        return Database.connect(conn_string, **conn_params)
+
+    def init_connection_state(self):
+        cursor = self.create_cursor(self.connection)
+        # Set the territory first. The territory overrides NLS_DATE_FORMAT
+        # and NLS_TIMESTAMP_FORMAT to the territory default. When all of
+        # these are set in single statement it isn't clear what is supposed
+        # to happen.
+        cursor.execute("ALTER SESSION SET NLS_TERRITORY = 'AMERICA'")
+        # Set oracle date to ansi date format.  This only needs to execute
+        # once when we create a new connection. We also set the Territory
+        # to 'AMERICA' which forces Sunday to evaluate to a '1' in
+        # TO_CHAR().
+        cursor.execute(
+            "ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS'"
+            " NLS_TIMESTAMP_FORMAT = 'YYYY-MM-DD HH24:MI:SS.FF'"
+            + (" TIME_ZONE = 'UTC'" if settings.USE_TZ else ''))
+        cursor.close()
+        if 'operators' not in self.__dict__:
+            # Ticket #14149: Check whether our LIKE implementation will
+            # work for this connection or we need to fall back on LIKEC.
+            # This check is performed only once per DatabaseWrapper
+            # instance per thread, since subsequent connections will use
+            # the same settings.
+            cursor = self.create_cursor(self.connection)
+            try:
+                cursor.execute("SELECT 1 FROM DUAL WHERE DUMMY %s"
+                               % self._standard_operators['contains'],
+                               ['X'])
+            except utils.DatabaseError:
+                self.operators = self._likec_operators
+            else:
+                self.operators = self._standard_operators
+            cursor.close()
+
+        try:
+            self.oracle_version = int(self.connection.version.split('.')[0])
+            # There's no way for the DatabaseOperations class to know the
+            # currently active Oracle version, so we do some setups here.
+            # TODO: Multi-db support will need a better solution (a way to
+            # communicate the current version).
+            if self.oracle_version <= 9:
+                self.ops.regex_lookup = self.ops.regex_lookup_9
+            else:
+                self.ops.regex_lookup = self.ops.regex_lookup_10
+        except ValueError:
+            pass
+        try:
+            self.connection.stmtcachesize = 20
+        except:
+            # Django docs specify cx_Oracle version 4.3.1 or higher, but
+            # stmtcachesize is available only in 4.3.2 and up.
+            pass
+
     def _cursor(self):
-        cursor = None
         if not self._valid_connection():
-            conn_string = convert_unicode(self._connect_string())
-            conn_params = self.settings_dict['OPTIONS'].copy()
-            if 'use_returning_into' in conn_params:
-                del conn_params['use_returning_into']
-            self.connection = Database.connect(conn_string, **conn_params)
-            cursor = FormatStylePlaceholderCursor(self.connection)
-            # Set the territory first. The territory overrides NLS_DATE_FORMAT
-            # and NLS_TIMESTAMP_FORMAT to the territory default. When all of
-            # these are set in single statement it isn't clear what is supposed
-            # to happen.
-            cursor.execute("ALTER SESSION SET NLS_TERRITORY = 'AMERICA'")
-            # Set oracle date to ansi date format.  This only needs to execute
-            # once when we create a new connection. We also set the Territory
-            # to 'AMERICA' which forces Sunday to evaluate to a '1' in
-            # TO_CHAR().
-            cursor.execute(
-                "ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS'"
-                " NLS_TIMESTAMP_FORMAT = 'YYYY-MM-DD HH24:MI:SS.FF'"
-                + (" TIME_ZONE = 'UTC'" if settings.USE_TZ else ''))
-
-            if 'operators' not in self.__dict__:
-                # Ticket #14149: Check whether our LIKE implementation will
-                # work for this connection or we need to fall back on LIKEC.
-                # This check is performed only once per DatabaseWrapper
-                # instance per thread, since subsequent connections will use
-                # the same settings.
-                try:
-                    cursor.execute("SELECT 1 FROM DUAL WHERE DUMMY %s"
-                                   % self._standard_operators['contains'],
-                                   ['X'])
-                except utils.DatabaseError:
-                    self.operators = self._likec_operators
-                else:
-                    self.operators = self._standard_operators
-
-            try:
-                self.oracle_version = int(self.connection.version.split('.')[0])
-                # There's no way for the DatabaseOperations class to know the
-                # currently active Oracle version, so we do some setups here.
-                # TODO: Multi-db support will need a better solution (a way to
-                # communicate the current version).
-                if self.oracle_version <= 9:
-                    self.ops.regex_lookup = self.ops.regex_lookup_9
-                else:
-                    self.ops.regex_lookup = self.ops.regex_lookup_10
-            except ValueError:
-                pass
-            try:
-                self.connection.stmtcachesize = 20
-            except:
-                # Django docs specify cx_Oracle version 4.3.1 or higher, but
-                # stmtcachesize is available only in 4.3.2 and up.
-                pass
+            conn_params = self.get_connection_params()
+            self.connection = self.get_new_connection(conn_params)
+            self.init_connection_state()
             connection_created.send(sender=self.__class__, connection=self)
-        if not cursor:
-            cursor = FormatStylePlaceholderCursor(self.connection)
-        return cursor
+        return self.create_cursor(self.connection)
 
     # Oracle doesn't support savepoint commits.  Ignore them.
     def _savepoint_commit(self, sid):