Laravel在迁移中删除外键
Laravel在迁移中删除外键
我想创建一个迁移,它将删除一个表。我创建了以下的迁移:
Schema::table('devices', function (Blueprint $table) { $table->increments('id'); $table->unsignedInteger('client_id')->nullable(); $table->foreign('client_id')->references('id')->on('clients')->onDelete('cascade'); });
现在我尝试这样删除它:
Schema::table('devices', function (Blueprint $table) { $table->dropForeign('devices_client_id_foreign'); $table->drop('devices'); });
但我收到以下错误信息:
In Connection.php line 664: SQLSTATE[42000]: Syntax error or access violation: 1091 Can't DROP 'devices_client_id_foreign'; check that column/key exists (SQL:
alter table
devices
drop foreign keydevices_client_id_foreign
)In PDOStatement.php line 144: SQLSTATE[42000]: Syntax error or access violation: 1091 Can't DROP 'devices_client_id_foreign'; check that column/key exists In PDOStatement.php line 142: SQLSTATE[42000]: Syntax error or access violation: 1091 Can't DROP 'devices_client_id_foreign'; check that column/key exists
在Laravel中,如果我们想要删除一个表的外键,我们需要在删除表之前先禁用外键检查,然后在删除完表之后再启用外键检查。具体的解决方法如下所示:
DB::statement('SET FOREIGN_KEY_CHECKS=0;'); Schema::dropIfExists('devices'); DB::statement('SET FOREIGN_KEY_CHECKS=1;');
然而,如果我们在创建一个迁移文件时需要添加和删除特定的列,上述方法就不适用了。例如,如果我们想要给users表添加一个列,但使用上述命令会删除整个users表,这可能是灾难性的。在这种情况下,更好的做法是在down方法中使用回滚操作。