code: func (c *Collection) SaveFields(fieldNames []string, model Model) error {
  	t := c.pool.NewTransaction()
  	t.SaveFields(c, fieldNames, model)
  	if err := t.Exec(); err != nil {
  		return err
  	}
  	return nil
  }
docs: // SaveFields saves only the given fields of the model. SaveFields uses
  // "last write wins" semantics. If another caller updates the the same fields
  // concurrently, your updates may be overwritten. It will return an error if
  // the type of model does not match the registered Collection, or if any of
  // the given fieldNames are not found in the registered Collection. If
  // SaveFields is called on a model that has not yet been saved, it will not
  // return an error. Instead, only the given fields will be saved in the
  // database.