code: func (engine *Engine) Update(bean interface{}, condiBeans ...interface{}) (int64, error) {
  	session := engine.NewSession()
  	defer session.Close()
  	return session.Update(bean, condiBeans...)
  }
docs: // Update records, bean's non-empty fields are updated contents,
  // condiBean' non-empty filds are conditions
  // CAUTION:
  //        1.bool will defaultly be updated content nor conditions
  //         You should call UseBool if you have bool to use.
  //        2.float32 & float64 may be not inexact as conditions