laravel errno 150 foreign key constraint is incorrectly formed

Question

Can anybody help me to solve this problem?

There are 3 tables with 2 foreign keys:

Schema::create(\'users\', function (Blueprint $table) {
    $table-&         


        

Answer 1

I tried all the answers provided in this thread.

Nothing worked.

Then I discovered I forgot to remove the "migrations" table in phpMyadmin.

I removed all tables from phpMyAdmin but the migrations table. That's why the error persisted again and again.

Answer 2

For PHP laravel 5.8 use unsigned modifier in this format

$table->unsignedBigInteger('user_id');

drop all tables in the database and run the migration again

Answer 3

we are table villes:

Schema::create('villes', function (Blueprint $table) {
            $table->bigIncrements('idVille'); // bigIncrement(8 bits)
            $table->string('nomVille');
            $table->timestamps();
        });

foreign key in table users for exemple :

Schema::table('users', function (Blueprint $table) {
            $table->bigInteger('ville_idVille')->unsigned()->after('tele');
            $table->foreign('ville_idVille')->references('idVille')->on('villes');
        });

Answer 4

public function up() {     Schema::create('companies', function (Blueprint $table) {         $table->bigIncrements('id');         $table->string('name');         $table->text('address');         $table->string('tel1');         $table->string('tel2');         $table->integer('owner');         $table->unsignedBigInteger('access_id');         $table->string('depot_number')->default(2);         $table->timestamps();           $table->foreign('access_id')->references('id')->on('accesses')             ->onDelete('cascade');     }); } 

public function up() {     Schema::create('accesses', function (Blueprint $table) {         $table->bigIncrements('id');         $table->string('type');         $table->string('description');         $table->timestamps();     }); } 

In your database/migrations folder, sort by name. Then make sure create_accesses_table is before create_companies_table here:

Answer 5

If the reference table primary key is in BigIcrements then Use the BigInteger for foreign key also like below

Table ATable

public function up()
{
    Schema::create('a_tables', function (Blueprint $table) {
        $table->bigIncrements('id');
   }
}

TABLE BTable

public function up()
{
    Schema::create('b_tales', function (Blueprint $table) {
    $table->bigIncrements('id');
    $table->bigInteger('a_tables_id')->unsigned();
     $table->foreign('a_tables_id')->references('id')->on('a_tables')->onDelete('cascade');
   }
}

Answer 6

Well this answer is related to Laravel 7.x. So the error:

errno: 150 "Foreign key constraint is incorrectly formed"

can occur due many reason while migrating the migrations. The one common reason that I am familiar about is order of migration.

Lets say we have two table "users" and "roles", and "users" table have a foreign key referring the "id" column on "roles" table. So make sure that "roles" is migrated before "users" table.

So order of migration is important. Its obvious as it does not make sense for MySQL to refer to "id" column of unknown table.

Second reason is wrong data type. In laravel 7.x we use "id()" method for primary key. So make sure that the intended foreign key (in my case "role_id" in "users" table) is of "bigInteger" and is "unsigned".

Here my code:

Schema::create('roles', function (Blueprint $table) {
        $table->id();
        $table->string('name');
        $table->string('slug')->nullable();
        $table->timestamps();
    });


Schema::create('users', function (Blueprint $table) {
        $table->id();
        $table->bigInteger("role_id")->unsigned();
        $table->string('name');
        $table->string('email')->unique();
        $table->timestamp('email_verified_at')->nullable();
        $table->string('password');
        $table->rememberToken();
        $table->timestamps();

        $table->foreign('role_id')->references('id')->on('roles')->onDelete('cascade');
    });

public function down()
{
    Schema::table('users', function(Blueprint $table)
    {
        $table->dropForeign('users_role_id_foreign'); 
    });
    Schema::dropIfExists('users');
}

So in the above code I had to migrate the "roles" table first then the "users" table. So MySQL can create foreign key for the roles table.

What is do is I move the child migration (migration having foreign key) to temporary folder. And restore it after migrating parent migration (in my case "roles" table and then migrate the child migration ("users" migration).

And as side tip: while dropping the dependent migration (migration containing foreign key) first drop the foreign key first. And Laravel uses specific naming convention while dropping foreign key "<table_name>_<foreign_key>_foreign".

So happy coding and be ready for Ground breaking release of PHP 8.