继承Django ManyRelatedManager的子类ManyToManyField

问题描述

有没有一种方法可以将Django ManyRelatedManager又称为ManyToManyField 的子类?

Is there a way to Subclass a Django ManyRelatedManager a.k.a. ManyToManyField ?

目标是在通过 deleted = None 标志调用 ManyRelatedManager 时对所有相关模型进行预过滤.如果 deleted = None ，则它是有效的 Model .

The goal is to pre-filter all related models when calling the ManyRelatedManager by a flag of deleted=None. If deleted=None then it is a valid Model.

到目前为止，这是代码，但似乎不起作用.

So far, this is the code, but it doesn't seem to work.

class ExcludeDeletedManyToManyField(models.ManyToManyField):

    def get_queryset(self):
        qs = super(ExcludeDeletedManyToManyField, self).get_queryset()
        return qs.filter(deleted__isnull=True)


class SelfRefrencingModel(models.Model):

    children = ExcludeDeletedManyToManyField('self', blank=True,
        symmetrical=False, related_name='parents')

推荐答案

您可以创建 SelfRefrencingModel 的rel ="nofollow">代理模型，并覆盖默认的经理.然后在 ManyToManyField 中使用此代理模型.

You can create proxy model of SelfRefrencingModel and override the default manager. Then use this proxy model in ManyToManyField.

对 ManyToManyField 进行子类化将无济于事，因为对于产生的查询集 ManyRelatedManger 是负责的.

Subclassing ManyToManyField will not help you because for the resulting queryset ManyRelatedManger is responsible.

代理模型方法:

from django.db import models

class A(models.Model):
    children = models.ManyToManyField('AProxy')
    name = models.TextField()
    deleted = models.NullBooleanField(null=True)


class FilterDeletedManager(models.Manager):
    def get_queryset(self):
        qs = super(FilterDeletedManager, self).get_query_set()
        return qs.filter(deleted__isnull=True)


class AProxy(A):
    objects = FilterDeletedManager()
    class Meta:
        proxy = True

使用这种方法的注意事项是，现在django希望 children 字段使用 AProxy 实例.

Caveat with this approach is that now django expects AProxy instances for children field.

因此，更好的可读性和可维护性的方法是在 __ init __ 中添加另一个属性.

So maybe better readable and maintainable approach will be to add another attribute in __init__.

from django.db import models

class A(models.Model):
    children = models.ManyToManyField('self')
    name = models.TextField()
    deleted = models.NullBooleanField(null=True)

    def __init__(self, *args, **kwargs):
        super(A, self).__init__(*args, **kwargs)
        self.deleted_null_children = self.children.filter(deleted__isnull=True)

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