我从未在python中找到DROP CASCADE的实现所以我最终写了我自己的。以下是它的外观：

  def delete_table（self，table_name，cascade = True）：

删除表'table_name'

 params =（self.quote_name（table_name），）
如果级联：
 conn = self._get_connection（） 

＃获取相关表的列表
 sql =SELECT T1.TABLE_NAME \ 
 FROM INFORMATION_SCHEMA.CONSTRAINT_TABLE_USAGE AS T1 \ 
 JOIN SYS.FOREIGN_KEYS AS F \ 
 ON（F.parent_object_id = OBJECT_ID（N'{0}'）OR \ 
 F.referenced_object_id = OBJECT_ID（N'{0}'））AND \ 
 T1 .CONSTRAINT_NAME = OBJECT_NAME（F.object_id）

 related_tables = self.execute（sql.format（params [0]））

＃删除所有约束
 constraints = self.execute（SELECT CONSTRAINT_NAME \ 
 FROM INFO RMATION_SCHEMA.TABLE_CONSTRAINTS \ 
 WHERE TABLE_NAME ='{0}'AND \ 
 CONSTRAINT_TYPE ='FOREIGN KEY';。format（table_name））

 sql =ALTER TABLE {0} DROP CONSTRAINT {1}; 
约束约束：
 self.execute（sql.format（params [0]，constraint [0]））

相关表中的表：
 self .delete_table（table [0]，cascade）

 sql =IF EXISTS（SELECT * \ 
 FROM sys.objects \ 
 WHERE object_id = OBJECT_ID（N' 0}'）AND \ 
 type in（N'U'））\ 
 DROP TABLE {0}

 self.execute（sql.format（params [ 0]））
 else：
 self.execute（'DROP TABLE％s;'％params）
 

I'm running a South migration in a Django project that uses Sql Server and pyodbc. This is backwards migration so the South is trying to delete a few of my tables.

The South executes the following method in order to drop the tables:

def delete_table(self, table_name, cascade=True):
    """
    Deletes the table 'table_name'.
    """
    params = (self.quote_name(table_name), )
    if cascade:
        self.execute('DROP TABLE %s CASCADE;' % params)
    else:
        self.execute('DROP TABLE %s;' % params)

drop_table = alias('delete_table')

The problem is that the Sql Server does not support cascade drops, so the migration fails with the following error:

pyodbc.ProgrammingError: ('42000', "[42000] [Microsoft][ODBC SQL Server Driver][SQL Server]Incorrect syntax near the keyword 'CASCADE'. (156) (SQLExecDirectW)")

I want to write to a patch for the South so that it works with the Sql Server. What would be the best way to simulate a DROP CASCADE? I think that both solutions using python or pure SQL would be valid.

I never found an implementation of the DROP CASCADE in python, so I ended up writing my own. Here is how it looks:

def delete_table(self, table_name, cascade=True):
    """
    Deletes the table 'table_name'.
    """
    params = (self.quote_name(table_name), )
    if cascade:
        conn = self._get_connection()

        # Get a list of related tables
        sql = "SELECT T1.TABLE_NAME \
                 FROM INFORMATION_SCHEMA.CONSTRAINT_TABLE_USAGE AS T1 \
                 JOIN SYS.FOREIGN_KEYS AS F \
                   ON (F.parent_object_id = OBJECT_ID(N'{0}') OR \
                      F.referenced_object_id = OBJECT_ID(N'{0}')) AND \
                      T1.CONSTRAINT_NAME = OBJECT_NAME(F.object_id)"

        related_tables = self.execute(sql.format(params[0]))

        # Drop all the constraints
        constraints = self.execute("SELECT CONSTRAINT_NAME \
                                    FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS \
                                    WHERE TABLE_NAME='{0}' AND \
                                    CONSTRAINT_TYPE='FOREIGN KEY';".format(table_name))

        sql = "ALTER TABLE {0} DROP CONSTRAINT {1};"
        for constraint in constraints:
            self.execute(sql.format(params[0], constraint[0]))

        for table in related_tables:
            self.delete_table(table[0], cascade)

        sql = "IF  EXISTS (SELECT * \
                           FROM sys.objects \
                           WHERE object_id = OBJECT_ID(N'{0}') AND \
                           type in (N'U')) \
               DROP TABLE {0}"

        self.execute(sql.format(params[0]))
    else:
        self.execute('DROP TABLE %s;' % params)