code: public function getRules(array $fields = [])
      {
          $default_rules = $this->model->getRules();
          
          if (count($fields) < 1) {
              return $default_rules;
          }
          
          foreach ($fields as $field => $rule) {
              if (is_int($field)) {
                  $rules[$rule] = $default_rules[$rule];
                  continue;
              }
              
              if (! key_exists($field, $default_rules)) {
                  continue;
              }
              
              $default_rules[$field] .= '|' . $rule;
          }
          
          $rules = [];
          $transformation = $this->model->getTransformation();
          foreach ($transformation as $original => $transformed) {
              $rules[$transformed] = $default_rules[$original];
          }
          
          foreach ($fields as $field => $rule) {
              if (! key_exists($field, $rules)) {
                  continue;
              }
              
              $rules[$field] .= '|' . $rule;
          }
          
          return $rules;
      }
docs: Rules of Entity
  
  @param array $fields
  @return array