1215 Cannot add foreign key constraint in laravel-CodePudding

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();
});

i'm new laravel, when i run migrate, in terminal show

SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL: alter table students add constraint students_city_id_foreign foreign key (city_id) references cities (id) on delete cascade)

help me fix

CodePudding user response：

Your problem is on the order of the code. You want to make a foreign key to a table which is not yet exists.

Try this instead:

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');
    });

Like this, you first creates both tables, and after that you set the foreign key.

CodePudding user response：

If you are using more recent version of Laravel id fields are now unsignedBigInteger field. So you should do something like:

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();
});

Also, make sure the cities migration is running before students.

CodePudding user response：

=>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.