如何在 MySQL 中临时禁用外键约束？

Question

Is it possible to temporarily disable constraints in MySQL?

I have two Django models, each with a ForeignKey to the other one. Deleting instances of a model returns an error because of the ForeignKey constraint:

cursor.execute("DELETE FROM myapp_item WHERE n = %s", n)
transaction.commit_unless_managed()  #a foreign key constraint fails here

cursor.execute("DELETE FROM myapp_style WHERE n = %s", n)
transaction.commit_unless_managed()

Is it possible to temporarily disable constraints and delete anyway?

转载于:https://stackoverflow.com/questions/15501673/how-to-temporarily-disable-a-foreign-key-constraint-in-mysql

Answer 1

Instead of disabling your constraint, permanently modify it to ON DELETE SET NULL. That will accomplish a similar thing and you wouldn't have to turn key checking on and off. Like so:

ALTER TABLE tablename1 DROP FOREIGN KEY fk_name1; //get rid of current constraints
ALTER TABLE tablename2 DROP FOREIGN KEY fk_name2;

ALTER TABLE tablename1 
  ADD FOREIGN KEY (table2_id) 
        REFERENCES table2(id)
        ON DELETE SET NULL  //add back constraint

ALTER TABLE tablename2 
  ADD FOREIGN KEY (table1_id) 
        REFERENCES table1(id)
        ON DELETE SET NULL //add back other constraint

Have a read of this (http://dev.mysql.com/doc/refman/5.5/en/alter-table.html) and this (http://dev.mysql.com/doc/refman/5.5/en/create-table-foreign-keys.html).