I have 3 tables called country,city,university

the country and city value displayed as dependent with each other now i want to put the university according to country and city in university table

country model-> protected $table = 'countries_tbl'; protected $primaryKey = 'id'; protected $fillable = ['name'];

public function cities() {
    return $this->hasMany(RegionModel::class);
}

city model->

protected $table = 'region_tbl';
protected $primaryKey = 'id';
protected $fk		='country_id';
protected $fillable = ['name'];

public function country(){
	return $this->belongsTo(CountryModel::class);
}
public function university() {
    return $this->hasMany(UniversityModel::class);
}

university model-> protected $table = 'university_info_tbl'; protected $primaryKey = 'id'; protected $fillable = ['name','university_id','region_id','university_address','university_short_descr','university_cover_img','university_logo_img','world_ranking',' acceptance_rate','avg_tuition_fees',' overview','admission_requirements,'];

public function product() {
          return $this->belongsTo(RegionModel::class);

}

Controller:

$university_add = new UniversityModel; $university_add->name= $request->input('name'); $save = $university_add->save(); if ($save) { return redirect()->back()->with('success', 'Save Successfully !!'); }