Laravel8 Many To Many change id for custom attribute - laravel

Question

I created a relationship many-to-many between Faculties and Departments(im Working in a prototype timetable problem). For a petition, these tables need a validation code vcode. The problems are in the relationship of this, I don't know why the relationship recognize only the id´s tables for the eloquent query and not the vcode.
attached my migrations and model relationship.
Migration Faculties Table
public function up()
{
Schema::create('faculties', function (Blueprint $table) {
$table->id();
$table->unsignedBigInteger('vcode')->index()->unique();
$table->string('code');
$table->string('name');
$table->string('website');
$table->string('email');
$table->string('phone');
$table->timestamps();
});
}
Relationshop on Faculty Model
public function departments()
{
return $this->belongsToMany(Department::class, 'faculty_departments','faculty_vcode','department_vcode');
}
Migration Departments Table
public function up()
{
Schema::create('departments', function (Blueprint $table) {
$table->id();
$table->unsignedBigInteger('vcode')->index()->unique();
$table->string('code');
$table->string('name');
$table->string('phone');
$table->string('email');
$table->string('website');
$table->timestamps();
});
}
Relationshop on Department Model
public function faculties()
{
return $this->belongsToMany(Faculty::class, 'faculty_departments', 'department_vcode','faculty_vcode',);
}
Migration FacultyDepartments (Relationship)
public function up()
{
Schema::create('faculty_departments', function (Blueprint $table) {
$table->id();
$table->unsignedBigInteger('faculty_vcode')->nullable()->index();
$table->foreign('faculty_vcode')
->references('vcode')
->on('faculties')
->cascadeOnUpdate()
->nullOnDelete();
$table->unsignedBigInteger('department_vcode')->nullable()->index();
$table->foreign('department_vcode')
->references('vcode')
->on('departments')
->cascadeOnUpdate()
->nullOnDelete();
$table->timestamps();
});
}
I provocate a error for get the query and tested the error (getting id´s table).
faculty::with('departments')->get() gives me:
select `departments`.*, `faculty_departments`.`faculty_vcode` as `pivot_faculty_vcode`, `faculty_departments`.`department_vcode` as `pivot_department_vcode`
from `departments`
inner join `faculty_departments` on `departments`.`id` = `faculty_departments`.`department_vcode`
where `faculty_departments`.`faculty_vcode` in (1, 2, 3, 4, 5, 6, 7)

Answer 1

Since you're not providing the field names for the faculties table or the departments table Laravel will assume it's the primary key (id) for those tables.
You need to update your belongsToMany method to be:
public function departments()
{
return $this->belongsToMany(
Department::class, // The related model
'faculty_departments', // The intermediate (pivot) table name
'faculty_vcode', // The pivot field relating to faculties
'department_vcode', // The pivot field relating to departments
'vcode', // The field on the faculties table
'vcode', // The field on the departments table
);
}