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我刚刚从 SQLite3 迁移到 Postgres 12（使用 pgloader）。

我无法删除某些模型对象，因为有其他模型对象引用它。

但是，我很确定我的模型对象在引用模型对象中设置了“on_delete = models.CASCADE”（在我的 Django 代码中的 models.py 中）。

所以我得到了 Postgres 生成的这个错误：

...
django.db.utils.IntegrityError: update or delete on table "app_reply" violates foreign key constraint "app_replyimage_reply_id_fkey" on table "app_replyimage"
DETAIL:  Key (id)=(SRB6Nf98) is still referenced from table "app_replyimage".

有没有办法（希望不用在 Postgres 中手动编辑表模式）来解决这个问题？

编辑：在下面添加一些代码...

模型.py

class ReplyImage(models.Model):
    id = models.CharField(default = make_id(), unique = True, primary_key = True, max_length = 8)
    
    file = models.ImageField(upload_to = customer_images_directory_path)
    
    reply = models.ForeignKey(Reply, on_delete = models.CASCADE, related_name = 'reply_images')
    
    #Meta
    created = models.DateTimeField(auto_now_add = True)
    updated = models.DateTimeField(auto_now = True)
    created_by = models.ForeignKey(User, on_delete = models.CASCADE, related_name = '+', null = True)
    updated_by = models.ForeignKey(User, on_delete = models.CASCADE, related_name = '+', null = True)
    
    def __str__(self):
        return str(self.id)
    
    def delete(self, *args, **kwargs):
        self.file.delete()
        super(ReplyImage, self).delete(*args, **kwargs)

@receiver(post_delete, sender = ReplyImage)
def reply_image_delete(sender, instance, **kwargs):
    instance.file.delete()

这是参考模型，回复：

class Reply(models.Model):
    id = models.CharField(default = make_id(), unique = True, primary_key = True, max_length = 8)
    
    #Content
    content = models.CharField(max_length = 560, blank = True, null = True)
    replies = GenericRelation('self')
    link = models.ForeignKey(Link, on_delete = models.SET_NULL, related_name = 'reply', blank = True, null = True)
    
    #Drip
    drip_interval_quantity = models.IntegerField(default = 0, blank = True, null = True) #Custom quantity
    drip_interval_calendar_unit = models.CharField(default = 'minute', max_length = 6, choices = DRIP_INTERVAL_CALENDAR_UNIT_CHOICES, blank = True, null = True) #Custom calendar unit
    
    post_datetime = models.DateTimeField(blank = True, null = True) #Post datetime
    
    #Twitter API
    self_status_id_str = models.CharField(max_length = 19, null = True, blank = True) #status_id_str of self
    in_reply_to_status_id_str = models.CharField(max_length = 19, null = True, blank = True) #status_id_str of tweet replied to
    
    #Meta
    created = models.DateTimeField(auto_now_add = True)
    updated = models.DateTimeField(auto_now = True)
    created_by = models.ForeignKey(User, on_delete = models.CASCADE, related_name = '+', null = True)
    updated_by = models.ForeignKey(User, on_delete = models.CASCADE, related_name = '+', null = True)
    
    #Mandatory fields for generic relation
    content_type = models.ForeignKey(ContentType, on_delete = models.CASCADE)
    object_id = models.CharField(default = make_id(), unique = True, max_length = 8)
    content_object = GenericForeignKey()
    
    customer = models.ForeignKey(Customer, on_delete = models.CASCADE, related_name = 'postreplies')
    
    def delete(self, *args, **kwargs):
        if self.reply_images.all():
            for i in self.reply_images.all():
                i.delete()
        
        if self.link:
            self.link.delete()
        
        super(Reply, self).delete(*args, **kwargs)
    
    def __str__(self):
        return self.content

@receiver(post_save, sender = Reply)
def reply_model_save(sender, instance, **kwargs):
    if kwargs['raw']:
        return
    
    recursive_reply_save_mock_post(instance)

@receiver(post_delete, sender = Reply)
def reply_model_delete(sender, instance, **kwargs):
    if instance.reply_images.all():
        for i in instance.reply_images.all():
            i.delete()

视图.py

...
post.replies.all().delete()
...

（我重新定义了 delete() 方法并添加了 post_delete() 信号，但我认为它们不会影响任何东西，因为它与 SQLite 完美配合。）

什么地方出了错？

编辑2：

Postgres 表架构

                       Table "public.app_replyimage"
    Column     |           Type           | Collation | Nullable | Default
---------------+--------------------------+-----------+----------+---------
 file          | text                     |           |          |
 created       | timestamp with time zone |           |          |
 updated       | timestamp with time zone |           |          |
 created_by_id | bigint                   |           |          |
 reply_id      | text                     |           |          |
 updated_by_id | bigint                   |           |          |
 id            | text                     |           | not null |
Indexes:
    "idx_85696_sqlite_autoindex_app_replyimage_1" PRIMARY KEY, btree (id)
    "idx_85696_app_replyimage_created_by_id_a5974d1f" btree (created_by_id)
    "idx_85696_app_replyimage_reply_id_7a8aff2c" btree (reply_id)
    "idx_85696_app_replyimage_updated_by_id_d73f7446" btree (updated_by_id)
Foreign-key constraints:
    "app_replyimage_created_by_id_fkey" FOREIGN KEY (created_by_id) REFERENCES auth_user(id)
    "app_replyimage_reply_id_fkey" FOREIGN KEY (reply_id) REFERENCES app_reply(id)
    "app_replyimage_updated_by_id_fkey" FOREIGN KEY (updated_by_id) REFERENCES auth_user(id)
4

1 回答 1

2

简而言之：Postgres 不处理ON DELETE 触发器。Django 本身进行级联处理。

实际上，models.CASCADE是一个可调用对象，它被调用并收集其他需要删除的元素。例如，我们可以查看源代码 [GitHub]：

def CASCADE(collector, field, sub_objs, using):
    collector.collect(
        sub_objs, source=field.remote_field.model, source_attr=field.name,
        nullable=field.null, fail_on_restricted=False,
    )
    if field.null and not connections[using].features.can_defer_constraint_checks:
        collector.add_field_update(field, None, sub_objs)

因此，这里collector是一个收集需要删除的对象的集合。

所以当你删除一个对象时，Django 会确定哪些其他对象需要被删除、更新等，然后以正确的顺序进行查询。它不使用数据库中的任何触发器。

实际上，您可以通过实现具有相同参数并运行不同逻辑的可调用对象来实现自己的删除策略，尽管我建议保持简单。

如果你想让 Django 做同样的事情，你应该改变这个字段，使它看起来像：

ALTER TABLE app_replyimage ALTER COLUMN reply_id
    integer REFERENCES orders ON DELETE CASCADE;
于 2020-07-18T22:14:05.423 回答