1215 无法在 laravel 中添加外键约束

Question

Schema::create('students', function (Blueprint $table) {
        $table->id();
        $table->integer('age')->unsigned();
        $table->integer('city_id')->unsigned();
        $table->foreign('city_id')->references('id')->on('cities')->onDelete('cascade');
        $table->timestamps();
});
Schema::create('cities', function (Blueprint $table) {
        $table->id();
        $table->text('name');
        $table->timestamps();
});

我是新的 laravel，当我运行迁移时，在终端显示

SQLSTATE [HY000]：一般错误：1215 无法添加外键约束（SQL：alter table students添加约束students_city_id_foreign外键（ city_id ）在删除级联时引用cities （ id ）

帮我修

Answer 1

您的问题出在代码顺序上。 您想为尚不存在的表创建外键。

试试这个：

Schema::create('students', function (Blueprint $table) {
        $table->id();
        $table->integer('age')->unsigned();
        $table->integer('city_id')->unsigned();
        $table->timestamps();
});

Schema::create('cities', function (Blueprint $table) {
        $table->id();
        $table->text('name');
        $table->timestamps();
});

Schema::table('students', function(Blueprint $table) {
        $table->foreign('city_id')->references('id')->on('cities')->onDelete('cascade');
    });

像这样，您首先创建两个表，然后设置外键。

Answer 2

如果您使用的是更新版本的 Laravel，则id字段现在是unsignedBigInteger字段。 因此，您应该执行以下操作：

Schema::create('cities', function (Blueprint $table) {
        $table->id();
        $table->text('name');
        $table->timestamps();
});
Schema::create('students', function (Blueprint $table) {
        $table->id();
        $table->integer('age')->unsigned();
        $table->foreignId('city_id')->constrained()->onDelete('cascade');
        $table->timestamps();
});

此外，请确保城市迁移在学生之前进行。

Answer 3

=>your cities migration first create then after students migration create because your city_id foreign key reference to the cities table laravel migration check order and order wise migration run so first cities migration run(cities table create) then students migration run.