BUG19972427: Fix creating of redundant connections in Django

The Connector/Python Django backend was creating too many database
connections since as soon as an object of DatabaseWrapper was
instanciated, a connection to the MySQL server was set up. This is
required to enable some version specific MySQL features.

We fix this by adding the cached_property decorator to the
mysql_version()-method.

Unit tests are updated and also fixes BUG#19954882.

Author: peeyushgupta

lib/mysql/connector/conversion.py

@@ -66,7 +66,11 @@ def set_unicode(self, value=True):
 
     def to_mysql(self, value):
         """Convert Python data type to MySQL"""
-        return value
+        type_name = value.__class__.__name__.lower()
+        try:
+            return getattr(self, "_{0}_to_mysql".format(type_name))(value)
+        except AttributeError:
+            return value
 
     def to_python(self, vtype, value):
         """Convert MySQL data type to Python"""

lib/mysql/connector/django/base.py

@@ -192,7 +192,7 @@ def __init__(self, connection):
         self.supports_microsecond_precision = self._microseconds_precision()
 
     def _microseconds_precision(self):
-        if self.connection.server_version >= (5, 6, 3):
+        if self.connection.mysql_version >= (5, 6, 3):
             return True
         return False
 
@@ -212,7 +212,7 @@ def _mysql_storage_engine(self):
             cursor.execute(droptable)
             cursor.execute('CREATE TABLE {table} (X INT)'.format(table=tblname))
 
-            if self.connection.server_version >= (5, 0, 0):
+            if self.connection.mysql_version >= (5, 0, 0):
                 cursor.execute(
                     "SELECT ENGINE FROM INFORMATION_SCHEMA.TABLES "
                     "WHERE TABLE_SCHEMA = %s AND TABLE_NAME = %s",
@@ -399,7 +399,7 @@ def sequence_reset_by_name_sql(self, style, sequences):
         # Truncate already resets the AUTO_INCREMENT field from
         # MySQL version 5.0.13 onwards. Refs #16961.
         res = []
-        if self.connection.server_version < (5, 0, 13):
+        if self.connection.mysql_version < (5, 0, 13):
             fmt = "{alter} {table} {{tablename}} {auto_inc} {field};".format(
                 alter=style.SQL_KEYWORD('ALTER'),
                 table=style.SQL_KEYWORD('TABLE'),
@@ -431,13 +431,7 @@ def value_to_db_datetime(self, value):
                     "MySQL backend does not support timezone-aware times."
                 )
 
-        try:
-            # Django 1.6
-            self.connection.ensure_connection()
-        except AttributeError:
-            if not self.connection.connection:
-                self.connection._connect()
-        return self.connection.connection.converter._datetime_to_mysql(value)
+        return self.connection.converter.to_mysql(value)
 
     def value_to_db_time(self, value):
         if value is None:
@@ -448,13 +442,7 @@ def value_to_db_time(self, value):
             raise ValueError("MySQL backend does not support timezone-aware "
                              "times.")
 
-        try:
-            # Django 1.6
-            self.connection.ensure_connection()
-        except AttributeError:
-            if not self.connection.connection:
-                self.connection._connect()
-        return self.connection.connection.converter._time_to_mysql(value)
+        return self.connection.converter.to_mysql(value)
 
     def year_lookup_bounds(self, value):
         # Again, no microseconds
@@ -467,7 +455,7 @@ def year_lookup_bounds_for_datetime_field(self, value):
         # Again, no microseconds
         first, second = super(DatabaseOperations,
             self).year_lookup_bounds_for_datetime_field(value)
-        if self.connection.server_version >= (5, 6, 4):
+        if self.connection.mysql_version >= (5, 6, 4):
             return [first.replace(microsecond=0), second]
         else:
             return [first.replace(microsecond=0),
@@ -522,15 +510,8 @@ class DatabaseWrapper(BaseDatabaseWrapper):
 
     def __init__(self, *args, **kwargs):
         super(DatabaseWrapper, self).__init__(*args, **kwargs)
-        self.server_version = None
-
-        # Since some features depend on the MySQL version, we need to connect
-        try:
-            # Django 1.6
-            self.ensure_connection()
-        except AttributeError:
-            self._connect()
 
+        self.converter = DjangoMySQLConverter()
         self.ops = DatabaseOperations(self)
         self.features = DatabaseFeatures(self)
         self.client = DatabaseClient(self)
@@ -584,14 +565,13 @@ def get_connection_params(self):
     def get_new_connection(self, conn_params):
         # Django 1.6
         cnx = mysql.connector.connect(**conn_params)
-        self.server_version = cnx.get_server_version()
         cnx.set_converter_class(DjangoMySQLConverter)
 
         return cnx
 
     def init_connection_state(self):
         # Django 1.6
-        if self.server_version < (5, 5, 3):
+        if self.mysql_version < (5, 5, 3):
             # See sysvar_sql_auto_is_null in MySQL Reference manual
             self.connection.cmd_query("SET SQL_AUTO_IS_NULL = 0")
 
@@ -737,6 +717,11 @@ def is_usable(self):
         # Django 1.6
         return self.connection.is_connected()
 
-    @property
+    @cached_property
     def mysql_version(self):
-        return self.server_version
+        config = self.get_connection_params()
+        temp_conn = mysql.connector.connect(**config)
+        server_version = temp_conn.get_server_version()
+        temp_conn.close()
+
+        return server_version

lib/mysql/connector/django/creation.py

@@ -30,6 +30,7 @@ def __init__(self, connection):
             'IntegerField': 'integer',
             'BigIntegerField': 'bigint',
             'IPAddressField': 'char(15)',
+
             'GenericIPAddressField': 'char(39)',
             'NullBooleanField': 'bool',
             'OneToOneField': 'integer',
@@ -42,7 +43,7 @@ def __init__(self, connection):
         }
 
         # Support for microseconds
-        if self.connection.get_server_version() >= (5, 6, 4):
+        if self.connection.mysql_version >= (5, 6, 4):
             self.data_types.update({
                 'DateTimeField': 'datetime(6)',
                 'TimeField': 'time(6)',

tests/test_django.py

@@ -198,7 +198,7 @@ def setUp(self):
 
     def test__init__(self):
         exp = self.conn.get_server_version()
-        self.assertEqual(exp, self.cnx.server_version)
+        self.assertEqual(exp, self.cnx.mysql_version)
 
         value = datetime.time(2, 5, 7)
         exp = self.conn.converter._time_to_mysql(value)
@@ -214,7 +214,9 @@ def test_signal(self):
 
         def conn_setup(*args, **kwargs):
             conn = kwargs['connection']
+            settings.DEBUG = True
             cur = conn.cursor()
+            settings.DEBUG = False
             cur.execute("SET @xyz=10")
             cur.close()
 
@@ -226,6 +228,22 @@ def conn_setup(*args, **kwargs):
         cursor.close()
         self.cnx.close()
 
+    def count_conn(self, *args, **kwargs):
+        try:
+            self.connections += 1
+        except AttributeError:
+            self.connection = 1
+
+    def test_connections(self):
+        connection_created.connect(self.count_conn)
+        self.connections = 0
+
+        # Checking if DatabaseWrapper object creates a connection by default
+        conn = DatabaseWrapper(settings.DATABASES['default'])
+        dbo = DatabaseOperations(conn)
+        dbo.value_to_db_time(datetime.time(3, 3, 3))
+        self.assertEqual(self.connections, 0)
+
 
 class DjangoDatabaseOperations(tests.MySQLConnectorTests):