Laravel: 1215 Cannot add foreign key constraint - when migrating

Question

I have table category which have parent of type of itself.

Schema::create('categories', function (Blueprint $table) {
        $table->bigIncrements('id');
        $table->string('name');
        $table->integer('parent_id')->unsigned()->nullable()->default(null);
        $table->foreign('parent_id')->references('id')->on('categories');
        $table->timestamps();
    });

Throws:

SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL: alter table `categories` add constraint `categories_parent_id_foreign` foreign key (`parent_id`) references `categories` (`id`))

I've already tried making parent_id as foreign in seperate, Schema::table function yet with no success. Table is InnoDB type.

why are you creating a FK that references the same table that you're creating? parent_id should reference id on the parents table — Piazzi
– Piazzi, Commented Mar 9, 2019 at 15:21
As I mentioned in first line, categories have parents of categories — TheRuthlessHacker
– TheRuthlessHacker, Commented Mar 9, 2019 at 15:27

Piazzi · Accepted Answer · 2019-03-09 15:30:10Z

2

Try changing your FK from integer to bigInteger:

$table->bigInteger('parent_id')->unsigned()->nullable()->default(null);

or

$table->unsignedBigInteger('parent_id')->nullable()->default(null);

edited Mar 9, 2019 at 15:30

answered Mar 9, 2019 at 15:12

Piazzi

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