SQLSTATE[23000]: Integrity constraint violation: 1217

Question

After creatin multiple migrations in my project, I wanted to rollback to update a few things but suddenly I got this error when I tried to drop projects table. I double checked the foreign key constrains but I can't find the error.

[Illuminate\Database\QueryException]                                         
  SQLSTATE[23000]: Integrity constraint violation: 1217 Cannot delete or upda  
  te a parent row: a foreign key constraint fails (SQL: drop table `projects`  
  )                                                                                                                                                           
  [PDOException]                                                               
  SQLSTATE[23000]: Integrity constraint violation: 1217 Cannot delete or upda  
  te a parent row: a foreign key constraint fails  

Here are my migrations: 1.create table users:

public function up()
    {
        Schema::create('users', function(Blueprint $table)
        {
            $table->increments('id');
            $table->string('first_name');
            $table->string('last_name');
            $table->string('email', 50)->unique();
            $table->string('password', 60);
            $table->string('password_temp', 60);
            $table->string('code', 60);
            $table->boolean('active');
            $table->string('remember_token', 100);
            $table->timestamps();
        });
    }
    public function down()
    {
        Schema::drop('users');
    }

2.create clients table:

public function up()
    {
        Schema::create('clients', function(Blueprint $table)
        {
            $table->increments('id');
            $table->integer('user_id')->unsigned()->index()->nullable();
            $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
            $table->timestamps();
        });
    }
    public function down()
    {
        Schema::drop('clients');
    }

3.create projects table:

public function up()
    {
        Schema::create('projects', function(Blueprint $table)
        {
            $table->increments('id');
            $table->string('name');
            $table->integer('status');
            $table->integer('client_id')->unsigned()->index()->nullable();
            $table->foreign('client_id')->references('id')->on('users')->onDelete('cascade');    
            $table->timestamps();
        });
    }
    public function down()
    {
        Schema::drop('projects');
    }

In the last migration, what could possibly be the mistake I am doing?! I face no trouble when migrating but it appears only when I rollback to add any changes.

Any idea why this happens?

Answer 1

If there are only 3 tables above mentioned, there is no issue in your migration as I have tried it myself with

php artisan migrate

to create the tables and

php artisan migrate:rollback

to rollback.

One thing that I know is Laravel is going to assume the sequence of the migration based on the migration file timestamp.

Therefore, I am quite sure there is another table that has a foreign key reference to the projects tables that has not been dropped as the error messsage is (SQL: drop table projects)

Try to use php artisan tinker and then Schema::drop('some_table_name'); where some_table_name is the table that has reference to projects table, then drop the projects table again.