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migrate时，在终端显示

SQLSTATE[HY000]：一般错误：1215无法添加外键约束(SQL:更改表students添加约束students_city_id_foreign外键(city_id(在删除级联上引用cities(id((

帮我修复

Answer 1

您的问题在于代码的顺序。您想要为尚未存在的表创建外键。

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，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Laravelid字段，则现在是unsignedBigInteger字段。所以你应该做一些类似的事情：

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，确保城市移民先于学生。

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.