Eloquent relationship returns null, but a similar one is fine

class Worker extends Eloquent{

    protected $fillable = ['first_name', 'last_name'];

    public function workhour(){
      return $this->hasMany('Workhour','workers_id');
    }
}

public function user()
{
    return $this->belongsTo('App\User','user_id');
}

@foreach ($profiles as $profile)
   {{ $profile->user->email }}
@endforeach

public function libri() {
    return $this->hasMany('App\Libro', 'id_autore')
}

public function transactionType() {
  return $this->hasOne("App\Model\TransactionType", "id");
}

public function transactionStatus() {
  return $this->hasOne("App\Model\TransactionStatus", "id");
}

public function transactionType() {
    return $this->hasOne("App\Model\TransactionType", "id", "transaction_type_id");
}

public function transactionStatus() {
    return $this->hasOne("App\Model\TransactionStatus", "id", "transaction_status_id");
}

public function post()
{
    return $this->belongsTo('App\Post', 'foreign_key', 'other_key');
}

public function user()
{
    return $this->belongsTo('App\User', 'foreign_key', 'other_key');
}