code: func (m *DbMap) Update(list ...interface{}) (int64, error) {
  	return update(m, m, list...)
  }
docs: // Update runs a SQL UPDATE statement for each element in list.  List
  // items must be pointers.
  //
  // Hook functions PreUpdate() and/or PostUpdate() will be executed
  // before/after the UPDATE statement if the interface defines them.
  //
  // Returns number of rows updated.
  //
  // Returns an error if SetKeys has not been called on the TableMap or if
  // any interface in the list has not been registered with AddTable.