Question

我想做一个自定义序列，例如：

如果它是数据库中的第一个对象，我将创建一个对象并将其命名为A001。

如果对象不断增加并达到A999，则名称将从B001开始。一旦达到B999，它将再次从C001开始。

Answer 1

我会在这里为您提供一个覆盖save方法的简单解决方案。

我们说我们有这个对象：

import string

class YourClass(models.Model):
    alph_counter = models.CharField(max_length=4, blank=True, null=True, verbose_name=_(u'Alphabet Counter'))

    def save(self, *args, **kwargs):
        if self.__class__.objects.all().count() == 0:
            # First object need to be set like this
            letter =  'A'
            number = 1

            # %03d used to write the number with 2 zeros before
            self.alphcounter = '%s%03d' (letter,number)  # 'A001' this time
        else:
            # Get the last object ID
            last_id = self.__class__.objects.all().order_by("-id")[0].id + 1

            # We need to know wich letter is it, we use division over ID
            wich_letter = (last_id+1) / 1000  
            letter = string.uppercasecase( wich_letter )
            number = (last_id+1) % 1000
            self.alphcounter = '%s%03d' (letter,number)

        super(self.__class__, self).save(*args, **kwargs)

如何创建自定义序列？

1 个答案: