MySQL Error 1215: Cannot add foreign key constraint

Question

I am trying to forward engineer my new schema onto my db server, but I can\'t figure out why I am getting this error. I\'ve tried to search for the answer here, but everyth

Answer 1

when try to make foreign key when using laravel migration

like this example:

user table

    public function up()
{
    Schema::create('flights', function (Blueprint $table) {
        $table->increments('id');
        $table->string('name');
        $table->TinyInteger('color_id')->unsigned();
        $table->foreign('color_id')->references('id')->on('colors');
        $table->timestamps();
    });
}

colors table

    public function up()
{
    Schema::create('flights', function (Blueprint $table) {
        $table->increments('id');
        $table->string('color');
        $table->timestamps();
    });
}

sometimes properties didn't work

[PDOException]
SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint

this error happened because the foreign key (type) in [user table] is deferent from primary key (type) in [colors table]

To solve this problem should change the primary key in [colors table]

$table->tinyIncrements('id');

---

When you use primary key $table->Increments('id');

you should use Integer as a foreign key

    $table-> unsignedInteger('fk_id');
    $table->foreign('fk_id')->references('id')->on('table_name');

---

When you use primary key $table->tinyIncrements('id');

you should use unsignedTinyInteger as a foreign key

    $table-> unsignedTinyInteger('fk_id');
    $table->foreign('fk_id')->references('id')->on('table_name');

---

When you use primary key $table->smallIncrements('id');

you should use unsignedSmallInteger as a foreign key

    $table-> unsignedSmallInteger('fk_id');
    $table->foreign('fk_id')->references('id')->on('table_name');

---

When you use primary key $table->mediumIncrements('id');

you should use unsignedMediumInteger as a foreign key

    $table-> unsignedMediumInteger('fk_id');
    $table->foreign('fk_id')->references('id')->on('table_name');