python – post_save信号和关系

2019年8月4日 186次阅读

我正在应用post_save信号来应用每个对象的用户权限,然后相应地过滤查询集.

我的模型是这样的：

class Project(models.Model):
    # Relations with other entities.
    employees = models.ManyToManyField('staff.Person', through='project.PersonProjectMembership',
                                       related_name='projects')
    research_groups = models.ManyToManyField('group.Group', related_name='projects',
                                             through='project.ProjectGroupMembership')
    departments = models.ManyToManyField('department.Department', related_name='projects',
                                         through='project.ProjectDepartmentMembership')

问题是：当我捕获保存后信号时,虽然我输入了部门的值,但研究组和研究组也是如此.员工,他们似乎总是空虚的.有什么我错过的吗？

更新：当前代码下方,尚未按预期工作.我已经用m2m_changed更改了post_save.

from django.db.models.signals import m2m_changed
from django.db import models
from django.dispatch.dispatcher import receiver

class Project(models.Model):
    employees = models.ManyToManyField('staff.Person', through='project.PersonProjectMembership',
    related_name='projects')

class PersonProjectMembership(models.Model):
    project = models.ForeignKey('project.Project', related_name="person_memberships")
    person = models.ForeignKey('staff.Person', related_name="project_memberships")
    lead = models.BooleanField(default=False)
    position = models.CharField(max_length=50)
    project_manager = models.BooleanField(
        default=False
    )

    class Meta:
        permissions = (
            ('view_personprojectmembership', _('View person project membership')),
        )

@receiver(m2m_changed, sender=Project.employees.through)
def _on_save_project_assign_privileges(sender, instance, action, reverse, model, pk_set, using, **kwargs):
    # [...]

解

在我的项目模型中,我明确地将PersonProjectMembership定义为m2m关系员工中的中间模型：

class Project(models.Model):
    # Relations with other entities.
    employees = models.ManyToManyField('staff.Person', through='project.PersonProjectMembership', related_name='projects')

保存项目的时间表如下：

> Project.save()
> PersonProjectMembership.save()

因此,在Project.post_save员工仍然是空的时候是正常的.我要做的就是收听PersonProjectMembership post_save信号：

@receiver(post_save, sender=PersonProjectMembership)
def my_listener(**kwargs):
    # do stuff [...]

查看https://docs.djangoproject.com/en/1.9/ref/models/fields/#django.db.models.ManyToManyField.through和https://docs.djangoproject.com/en/1.9/topics/signals/

最佳答案 您可能知道,Many2Many关系是通过附加表存储的,其中包含来自关系两端的主键.因此,使用Many2Many关系保存模型实例是两个步骤：

>首先,实例是保存：创建数据库中的新记录,实例接收它的主键. post_save此时被解雇了.
>之后,保存关系：创建关系表中的记录.此时正在发射m2m变化的信号.

换句话说,当触发post_save时,还没有处理m2m关系.

您可以查看文档：m2m-changed

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