public function fields()
    {
        $fields = parent::fields();
        $fields['id'] = 'treaty_id';

        $fields['academic_plan_name'] = function ($model) {
            return $this->getAcademicPlan()->one()->name;
        };

        $fields['enrollee_list'] = function($model) {
            return $this->getEnrollees()->all();
        };

        return $fields;
    }

    public function getEnrollees() {
        return $this->hasMany(EnrolleeModel::className(), ['treaty_id' => 'treaty_id']);
    }