DataBase/app/Project.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Project extends Model
{
    public function directors() 
    {
        return $this->belongsTo(Director::class, 'director_id', 'id');
    }

    public function spheres() 
    {
        return $this->belongsTo(Sphere::class, 'sphere_id', 'id');
    }

    public function employees()
    {
        return $this->belongsToMany(Employee::class, 'emploee_projects');
    }
}