code: func (c *Collection) Exists(id string) (bool, error) {
  	t := c.pool.NewTransaction()
  	exists := false
  	t.Exists(c, id, &exists)
  	if err := t.Exec(); err != nil {
  		return false, err
  	}
  	return exists, nil
  }
docs: // Exists returns true if the collection has a model with the given id. It
  // returns an error if there was a problem connecting to the database.