django - 相对于前一个值在 Django 中自动增加一个值

Question

有没有办法相对于前一个字段自动增加一个字段...例如，如果前一个记录的值是 09-0001，那么下一个记录应该分配 09-0002 等等...想法？我正在考虑覆盖保存方法，但我不太确定

Answer 1

Django 不会让您在模型中拥有多个 AutoField，并且您已经拥有一个作为主键。因此，您必须覆盖 save 并且可能需要回顾表格以找出要增加的内容。

像这样的东西：

class Product(models.Model): 
   code = models.IntegerField()
   number = models.IntegerField()
   ...

   def get_serial_number(self): 
      "Get formatted value of serial number"
      return "%.2d-%.3d" % (self.code, self.product)

   def save(self): 
      "Get last value of Code and Number from database, and increment before save"
      top = Product.objects.order_by('-code','-number')[0]
      self.code = top.code + 1
      self.number = top.number + 1
      super(Product, self).save()

   # etc.

请注意，如果您的保存方法中没有某种锁定，您可能会遇到并发问题（两个线程试图在代码和数字中存储相同的值）。

Answer 2

AutoField is the field type that Django uses for the model base class' 'id' property, but you can use it for additional autoincremented fields.

I don't think you can do any formatting like in your example, but a good approach would be to make a custom field type that overrides the save() method to perform the desired formatting.

Answer 3

在 SQL 中：

+-------+------------------+------+-----+---------+----------------+
| Field | Type             | Null | Key | Default | Extra          |
+-------+------------------+------+-----+---------+----------------+
| code  | int(11) unsigned | NO   | PRI | NULL    | auto_increment |
+-------+------------------+------+-----+---------+----------------+

在 Django 中：

self.code = None
self.number = top.number + 1
self.save() # or super(Product, self).save()

保存后code会自动增加。