Eloquent ORM relationship always return null in laravel

Question

I have 3 Models:

MonHoc Model:

class MonHoc extends Model{
   protected $table='monhoc' ;
   protected $fillable = [
      'mamh', 'phuongthucgiangday', 'tenmh','tinchitichluy','tinchihocphi','hockydenghi',
   ];

   public function monTienQuyet(){
      return $this->hasMany('App\MonTQ','montq_id','id');
   }

   public function monTuyChon(){
      return $this->hasMany('App\MonTC','montc_id','id');
   }
}

MonTC model:

class MonTC extends Model{
   protected $table='monhoc_tuychon' ;
   protected $fillable = [
      'monhoc_id', 'montc_id',
   ];
   public function monhoc(){
      return $this->belongsTo('App\MonHoc','monhoc_id');
   }
}

MonTQ model:

class MonTQ extends Model{
   protected $table='montienquyet' ;
   protected $fillable = [
      'monhoc_id', 'montq_id',
   ];    
   public function monhoc(){
      return $this->belongsTo('App\MonHoc','monhoc_id');
   }
}

but when I use MonHoc model in controller:

public function test(MonHoc $monhoc){
   $mon=$monhoc->monTienQuyet->toSql();
   dd($mon);
}

it show SQL

select * from `montienquyet` where `montienquyet`.`montq_id` is null and `montienquyet`.`montq_id` is not null

It show null in MySQL because the where clause is the opposite. I don't know why the model export this SQL!

Please help!

Answer 1

Please try this one:

For hasMany :

return $this->hasMany(MonTC::class, 'montc_id');

For belongsTo :

return $this->belongsTo(MonHoc::class, 'monhoc_id');

Another solution is:

return $this->hasMany('App\Models\MonTC', 'montc_id');

And

return $this->belongsTo('App\Models\MonHoc', 'monhoc_id');

Answer 2

Check this:

public function test(MonHoc $monhoc){
   $monhoc = $monhoc->find(1) //the id that exists
   $mon=$monhoc->monTienQuyet;
   dd($mon);
}