django - 如何使用直通表并指向 self 使用 ManyToManyField 设置 related_name

Question

我有一个任务类，可以有子任务，所以这是一个循环关系。我通过链接器模型/表传递它，如下所示:

class Task(models.Model):
    title = models.CharField(max_length=100)
    description = models.TextField(blank=True)
    completed = models.BooleanField(default=False)
    project = models.ForeignKey('Project', related_name="tasks")
    dependancy = models.ManyToManyField('self', through='Dependancy', null=True, 
        blank=True, through_fields=('task', 'sub_task'), symmetrical=False)
    def __str__(self):
        return self.title

class Dependancy(models.Model):
    task = models.ForeignKey(Task)
    sub_task = models.ForeignKey(Task)

但我收到此错误:

ERRORS:
gantt_charts.dependency.sub_task: (fields.E303) Reverse query name for 'dependency.sub_task' clashes with field name 'Task.dependency'.
        HINT: Rename field 'Task.dependency', or add/change a related_name argument to the definition for field 'dependency.sub_task'.
gantt_charts.dependency.sub_task: (fields.E304) Reverse accessor for 'dependency.sub_task' clashes with reverse accessor for 'dependency.task'.
        HINT: Add or change a related_name argument to the definition for 'dependency.sub_task' or 'dependency.task'.


gantt_charts.dependency.task: (fields.E303) Reverse query name for 'dependency.task' clashes with field name 'Task.dependency'.
        HINT: Rename field 'Task.dependency', or add/change a related_name argument to the definition for field 'dependency.task'.
gantt_charts.dependency.task: (fields.E304) Reverse accessor for 'dependency.task' clashes with reverse accessor for 'dependency.sub_task'.
        HINT: Add or change a related_name argument to the definition for 'dependency.task' or 'dependency.sub_task'.

显然我需要在 Dependency.sub_task 和 Dependency.task 字段上设置相关名称，并遵循解决方案 here是将它们命名为 task_task和 task_sub_task ，但这听起来是错误的、不直观且令人困惑的。

什么是他们的清晰简洁的名称？如果我在使用链接表时不会对相关名称是什么感到困惑，那会更容易。

Answer 1

给定一个 Task例如，您如何访问所有 Dependencies将其作为他们的 task ?或者他们的 sub_task ?这就是related_name的目的— 它提供了 Django 将在 Task 上创建的属性的名称指向那组东西。

您看到该错误是因为 Django 自动使用名称 <model>_set ，并且由于您有两个 ForeignKeys指向同一个模型，默认名称会发生​​冲突。

现在，您可能永远不需要直接访问 Dependencies那样。如果是这种情况，您可以添加 related_name='+'到这两个字段，并且根本不会创建 reverse 属性(并且您的错误将消失)。

如果您确实想访问它们，名称由您决定。我更喜欢更长但更具描述性的名称，以明确其目的。我可能会像这样对问题进行建模:

class Task(models.Model): 
    subtasks = models.ManyToManyField('self', 
                                      through='Dependancy',
                                      symmetrical=False,
                                      through_fields=('supertask', 'subtask'),
                                      related_name='supertasks')

class Dependancy(models.Model):
    supertask = models.ForeignKey(Task, related_name='dependencies_as_supertask')
    subtask = models.ForeignKey(Task, related_name='dependencies_as_subtask')

    class Meta:
        unique_together = ('supertask', 'subtask')


>>> task = Task.objects.get()

>>> # all the Tasks that are supertasks of this one
>>> task.supertasks

>>> # all the Tasks that are subtasks of this one
>>> task.subtasks

>>> # all the Dependencies with this Task as the supertask
>>> task.dependencies_as_supertask

>>> # all the Dependencies with this Task as the subtask
>>> task.dependencies_as_subtask