[django] backport savepoints for MySQL

mysql_backports.py

from django.db.backends import BaseDatabaseFeatures
from django.db.backends.mysql.base import (
    DatabaseFeatures as MySQLDatabaseFeatures,
    DatabaseOperations as MySQLDatabaseOperations,
)

try:
    from django.util.functional import cached_property
except ImportError:
    # Backport from django 1.4
    class cached_property(object):
        """
        Decorator that creates converts a method with a single
        self argument into a property cached on the instance.
        """
        def __init__(self, func):
            self.func = func

        def __get__(self, instance, type):
            res = instance.__dict__[self.func.__name__] = self.func(instance)
            return res


class Features(object):
    # Backport from django 1.4
    @cached_property
    def _mysql_storage_engine(self):
        "Internal method used in Django tests. Don't rely on this from your code"
        cursor = self.connection.cursor()
        cursor.execute('CREATE TABLE INTROSPECT_TEST (X INT)')
        # This command is MySQL specific; the second column
        # will tell you the default table type of the created
        # table. Since all Django's test tables will have the same
        # table type, that's enough to evaluate the feature.
        cursor.execute("SHOW TABLE STATUS WHERE Name='INTROSPECT_TEST'")
        result = cursor.fetchone()
        cursor.execute('DROP TABLE INTROSPECT_TEST')
        return result[1]

    # Backport from django 1.4 + fix to check for InnoDB
    @property
    def uses_savepoints(self):
        return self._mysql_storage_engine == 'InnoDB' or \
            self.get_server_version() >= (5, 0, 3)

    # django 1.4 will set this property, so stub it
    @uses_savepoints.setter
    def uses_savepoints(self, value):
        pass


if Features not in MySQLDatabaseFeatures.__bases__:
    MySQLDatabaseFeatures.__bases__ = (Features, ) + MySQLDatabaseFeatures.__bases__


# Backport from django 1.4
class Operations(object):
    def savepoint_create_sql(self, sid):
        return "SAVEPOINT %s" % sid

    def savepoint_commit_sql(self, sid):
        return "RELEASE SAVEPOINT %s" % sid

    def savepoint_rollback_sql(self, sid):
        return "ROLLBACK TO SAVEPOINT %s" % sid


if Operations not in MySQLDatabaseOperations.__bases__:
    MySQLDatabaseOperations.__bases__ = (Operations, ) + MySQLDatabaseOperations.__bases__