在Django中设置ManyToMany字段的默认值的正确方法 [英] The right way to set the default value of a ManyToMany field in django

问题描述

设置many2many字段的默认值的正确方法是什么?这是我在下面尝试的，但是没有用.我知道我可以覆盖save方法，但是每次更新模型时都不会调用该方法吗?我只想在每次创建实例时设置模型的初始值.

What is the right way to set the default value of a many2many field? This is what I tried below but it is not working. I know that I could override the save method, but wouldn't that be called every time the model gets updated? I want to only set the initial values of the model every time an instance is created.

def default_values():
     return [c.id for c in SomeOtherModel.objects.filter(otherfield__isnull = True)]


class SomeModel(models.Model):
    somefield = models.ManyToManyField('SomeField', default=default_values)
    semeotherfield = models.ForeignKey('SomeOtherField')

我正在使用Django 1.8

I am using django 1.8

推荐答案

您可以覆盖save方法，并在其中插入一个检查主键是否为空的方法.如果为空-这是对象的创建.

You can override save method, and inside that insert a check if primary key is empty or not. If it's empty - this is creation of object.

还可以连接到保存后的信号-属性告诉您这是否是对象的创建.

Also you can connect to post save signal - there is attribute telling you if this is creation of object or not.

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