django - 如何将计算字段添加到 django admin inline

Question

我正在尝试将计算字段添加到 Django 管理内联中。考虑这组类:

models.py:

class MyGroup(models.Model):
  group_name = models.CharField()
  size = models.IntegerField()

class MyUser(models.Model):
  user_name = models.CharField()
  groups = models.ManyToMany(MyGroup, related_name="users", through=MyMembership)
    
class MyMembership(models.Model):
  group = models.ForeignKey(MyGroup)
  user = models.ForeignKey(MyUser)
  timestamp = models.DateTimeField(auto_add_now=True)

我想在内联中显示group.size字段。我认为以下代码可以工作(基于 this answer ):

admin.py:

class MyMembershipInline(admin.TabularInline):
  model = MyUser.groups.through
  fields = (
    "group",
    "timestamp",
    "size",
  )
  readonly_fields = (
    "timestamp",
    "size",
  )

  def size(self, instance):
    return instance.group.size

@admin.register(MyUser):
class MyUserAdmin(admin.ModelAdmin)
  fields = ("user_name",)
  inlines = (MyMembershipInline,)

但我收到以下错误:

Unknown field(s) (size) specified for MyMembership

有什么建议吗？

Answer 1

在寻找此问题的解决方案时，我在以下 URL 中找到了一个适合我的解决方案: https://www.boris.co/2013/04/computed-field-on-tabularinline.html

给出的例子是:

class StatsInline(admin.TabularInline):
    model = Stats
    fields = ('clicked', 'shown', 'avg')
    readonly_fields = ('avg',)
    verbose_name = 'Stats'
    verbose_name_plural = 'Stats'
    can_delete = False

    def avg(self, obj):
        return float(obj.clicked) / obj.shown if obj.shown else 0

需要在 fields 和 readonly_fields 属性中提供计算字段。