Laravel Foreign key Referencing table in External database? - php

Question

I'm new to Laravel and databases in general. I'm writing a web application for student evaluations. I have an existing MySQL database that contains everything I need already; however, I am using Laravel's auth user table and trying to add a foreign key that references a Teacher table in the MySQL database. I keep getting the following error...
php artisan migrate:fresh
In Connection.php line 664:
SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint
(SQL: alter table users add constraint users_teacher_id_foreign
foreign key (teacher_id) references p4j.teacher (teacher_id))
In Connection.php line 458: SQLSTATE[HY000]: General error: 1215 Cannot
add foreign key constraint
My code is as follows...
config/database.php
'mysql' => [
'driver' => 'mysql',
'host' => env('DB_HOST', '127.0.0.1'),
'port' => env('DP_PORT', '3306'),
'database' => env('DB_DATABASE', 'p4j'),
'username' => env('DB_USERNAME', 'root'),
'password' => env('DP_PASSWORD', '**mypassword**'),
'charset' => 'utf8',
'collation' => 'utf8_unicode_ci',
'prefix' => '',
],
database/migrations/2014_10_12_000000_create_users_table.php
public function up()
{
Schema::create('users', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
$table->string('email')->unique();
$table->string('password');
$table->integer('teacher_id')->unsigned();
$table->rememberToken();
$table->timestamps();
});
Schema::table('users', function (Blueprint $table) {
$table->foreign('teacher_id')->references('teacher_id')->on('p4j.teacher');
});
}
app/User.php
protected $fillable = [
'name', 'email', 'password', 'teacher_id'
];
/**
* The attributes that should be hidden for arrays.
*
* #var array
*/
protected $hidden = [
'password', 'remember_token',
];

Answer 1

You just need to make sure that the data type of the foreign key (p4j.teacher.teacher_id) corresponds to the same data type of the teacher_id column in your users table.
We need to see the structure of the p4j.teacher table.

Answer 2

Couple possible issues and solutions are that your db engine is not INNODB or loading order of migration files is incorrect. For the first solution you need to add $table->engine = 'InnoDB'; inside of Schema::create and if this doesn't fix the issue, i'll need you to post the names of your users and teacher migrations
Possible fix:
Both PRIMARY KEY constraint and UNIQUE constraint uses to enforce Entity integrity (defines a row as a unique entity for a particular table), but primary keys do not allow null values. Specifies the column that uniquely identifies a row in the table. The identified columns must be defined as NOT NULL.
And since laravel increment function also
Auto-incrementing UNSIGNED INTEGER (primary key) equivalent column.
Simply removing ->default(null); and rerunning migrations should potentially fix the problem.