php - 如何在 laravel 5.2 迁移中删除包含外键的组合键

Question

我有一个表(名为 j_stones)，它包含 5 个字段:

id(primary key)  
j_stones_type(foreign-key)  
shape  
size  
carat

我想让每一行都是唯一的，所以我创建了一个迁移来做到这一点:

public function up()
    {
        Schema::table('j_stones', function (Blueprint $table) {
            $table->unique(['j_stone_types_id','shape','size','carat']);
        });
    }

这很好用，但是当我尝试回滚时出现以下错误:

1[照亮\数据库\查询异常]

SQLSTATE[HY000]: General error: 1553 Cannot drop index

'j_stones_j_stone_types_id_shape_size_carat_unique': needed in a foreign key constraint (SQL: alter table j_stones drop index j_stones_j_stone_types_id_shape_size_carat_unique)

[PDOException] SQLSTATE[HY000]: General error: 1553 Cannot drop index 'j_stones_j_stone_types_id_shape_size_carat_unique': needed in a foreign key constraint'

这是我的回滚代码:

    public function down()
{
    Schema::table('j_stones', function (Blueprint $table) {
        $table->dropUnique(['j_stone_types_id','shape','size','carat']);
    });
}

我试过像这样禁用外键约束:

    public function down()
{
    DB::statement('SET FOREIGN_KEY_CHECKS = 0'); 
    Schema::table('j_stones', function (Blueprint $table) {

        $table->dropUnique(['j_stone_types_id','shape','size','carat']);
    });
    DB::statement('SET FOREIGN_KEY_CHECKS = 1'); 
}

还有这样的:

    public function down()
{
    Schema::disableForeignKeyConstraints();
    Schema::table('j_stones', function (Blueprint $table) {

        $table->dropUnique(['j_stone_types_id','shape','size','carat']);
    });
    Schema::enableForeignKeyConstraints();
}

但是在回滚时仍然不断发生错误。
我将 MySql 与 InnoDb 一起使用。

请指教。

编辑:
我使用以下 hack 进行了回滚，但仍在寻找合适的解决方案:

    public function down()
{

    Schema::table('j_stones', function (Blueprint $table) {
        $table->dropForeign(['j_stone_types_id']);
        $table->dropUnique(['j_stone_types_id','shape','size','carat']);
    });

}

Answer 1

这里是这个 reported Laravel bug 的解决方法

public function up() {
    Schema::table('contact_tags', function (Blueprint $table) {            
        $table->unique(['tag_id', 'contact_id'], 'tag_contact_unique'); //so that contact cannot have the same tag multiple times
    });
}

public function down() {
    Schema::table('contact_tags', function (Blueprint $table) {
        //THE FOLLOWING 2 COMMANDS ARE THE WORKAROUND
        //Although this feels weird, we first need to add the missing indexes:
        $table->index('tag_id', 'tag_id_foreign');
        $table->index('contact_id', 'contact_id_foreign');

        //Now proceed with the main part of this "down" command to drop the unique index:
        $table->dropUnique('tag_contact_unique');
    });
}