Laravel migration: “Foreign key constraint is incorrectly formed” (errno 150)

Question

When migrating my DB, this error appears. Below is my code followed by the error that I am getting when trying to run the migration.

Code

Answer 1

Please add ->nullable() on your field and make sure that all the fields you're referring to really exist.

Answer 2

When creating a new table in Laravel. A migration will be generated like:

$table->bigIncrements('id');

Instead of (in older Laravel versions):

$table->increments('id');

When using bigIncrements the foreign key expects a bigInteger instead of an integer. So your code will look like this:

public function up()
    {
        Schema::create('meals', function (Blueprint $table) {
            $table->increments('id');
            $table->unsignedBigInteger('user_id'); //changed this line
            $table->unsignedBigInteger('category_id'); //changed this line
            $table->string('title');
            $table->string('body');
            $table->string('meal_av');
            $table->timestamps();

            $table->foreign('user_id')
                ->references('id')
                ->on('users')
                ->onDelete('cascade');

            $table->foreign('category_id')
                ->references('id')
                ->on('categories')
                ->onDelete('cascade');
        });
    }  

You could also use increments instead of bigIncrements like Kiko Sejio said.

The difference between Integer and BigInteger is the size:

• int => 32-bit
• bigint => 64-bit

Answer 3

I got the same message for data type miss-matched problem.

I used bigIncrements() for 'id' and when I used it as foreign key (used bigInteger()) I got the error.

I have found the solution, bigIncrements() returns unsignedBigInteger. So need to use unsignedBigInteger() instead of bigInteger() in foreign key

Sharing this because it might help others

Answer 4

Laravel 6: Update on 17 Jan 2020

$table->bigInteger( 'category_id' )->unsigned();

This worked well for me