SQLSTATE[HY000]: General error: 1005 Can’t create table `school`.`posts` (errno: 150 “Foreign key constraint is incorrectly formed”)

before everything, I tried hard many websites and forums to solve this problem until these posts related to this problem in StackOverflow, but I can’t solve the problem. I want to create to one to many relationship between Post and Category model but I get that error code.

SQLSTATE[HY000]: General error: 1005 Can’t create table school.posts (errno: 150 “Foreign key constraint is incorrectly formed”) (SQL: alter table posts add constraint posts_category_id_foreign foreign key (category_id) references categories (id) on delete cascade)

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

        Schema::create('posts', function (Blueprint $table) {
            $table->id();
            $table->integer('category_id')->unsigned();
            $table->foreign('category_id')->nullable()->references('id')->on('categories');
            $table->string('title')->nullable();
            $table->timestamps();
        });
    }

class Category extends Model
{
    use HasFactory;

    protected $table = 'categories';

    protected $guarded = [];


    public function posts(){
        return $this->hasMany(Post::class);
    }
}

class Post extends Model
{
    use HasFactory;

    protected $guarded = [];

    public function category(){
        return $this->belongsTo(Category::class);
    }


}

please help me I appreciate your help.

Answer

Your foreign_key field and your id should be of the same type, for example, if categories.id is bigIncrements, your foreign_key inside your Post table also should be bigInteger.

Category Table

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

Post Table

Schema::create('posts', function (Blueprint $table) {
    $table->id();
    $table->bigInteger('category_id')->unsigned()->nullable();
    $table->foreign('category_id')->references('id')->on('categories')->onDelete('cascade');
    $table->string('title')->nullable();
    $table->timestamps();
});

Note: You should make sure, your Category Table migration is running before Post Table migration.