今天要來使用ORM來寫入model data，讓我們能針對model data做新增、讀取、更新和刪除(CRUD)。
基本上會用這三種:

• .create(values) 在model 上建立一筆新紀錄 會傳回已建立的紀錄

• .write(values) 使用已有的值，更新recordest (returns nothing)

• .unlink() 從資料庫刪除紀錄，(returns nothing)
  ex:我們要預防在「Borrowed」或「Returned」的states，直接建立新的記錄。
  (create)到library_checkout/models/library_checkout.py

@api.model
    def create(self, vals):
        new_record = super().create(vals)
        if new_record.stage_id.state in ("open", "close"):
            raise exceptions.UserError(
                "State not allowed for new checkouts."
            )
        return new_record

ex: 租借出去的書，應該要持續追蹤書籍的借出日期和歸還日期。
(write)先到library_checkout/models/library_checkout.py，新增兩個日期欄位

    checkout_date = fields.Date(readonly=True)
    close_date = fields.Date(readonly=True)

回到library_checkout/models/library_checkout.py

   def write(self, vals):
      old_state = self.stage_id.state
      super().write(vals)
      new_state = self.stage_id.state
      if not self.env.context.get("_checkout_write"):
          if new_state != old_state and new_state == "open":
              self.with_context(_checkout_write=True).write(
                  {"checkout_date": fields.Date.today()})
          if new_state != old_state and new_state == "done":
              self.with_context(_checkout_write=True).write(
                  {"close_date": fields.Date.today()})
      return True

另外原本request date預設為今天，如果被更改的話，應該要向使用者提醒，運用onchange來修改，只會在:
還是到library_checkout/models/library_checkout.py

  @api.depends('member_id')
    def _compute_request_date_onchange(self):
        today_date = fields.Date.today()
        if self.request_date != today_date:
            self.request_date = today_date
            return {
                "warning": {
                    "title": "Changed Request Date",
                    "message": "Request date changed to today!",
                }
            }
    
    checkout_date = fields.Date(readonly=True)
    close_date = fields.Date(readonly=True)