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python - 派生查询上的 Django 内部联接

问题描述

我有两个模型如下所示。我希望能够通过 django ORM 执行这个查询，基本上给了我 CustomUser 类以及两个派生字段：max(message.sent_at) 和 max(case when read_at is null then 1 else 0 end)。这两个字段使我能够按用户名和最新活动对消息线程进行排序。

这是我的课程：

class CustomUser(AbstractBaseUser, PermissionsMixin):
    username_validator = UnicodeUsernameValidator()

    username = models.CharField(_('username'), max_length=150, unique=True, help_text=_('Required. 150 characters or fewer. Letters, digits and @/./+/-/_ only.'), validators=[username_validator], error_messages={'unique': _('A user with that username already exists.'),},)
    email = models.EmailField(_('email address'), blank=True)
    first_name = models.CharField(_('first name'), max_length=30, blank=True)
    last_name = models.CharField(_('last name'), max_length=150, blank=True)
    is_staff = models.BooleanField(_('staff status'), default=False, help_text=_('Designates whether the user can log into this admin site.'),)
    is_active = models.BooleanField(_('active'), default=True, help_text=_('Designates whether this user should be treated as active. Unselect this instead of deleting accounts.'),)
    date_joined = models.DateTimeField(_('date joined'), default=timezone.now)
    bio = models.TextField(max_length=500, null=True, blank=True)
    location = models.CharField(max_length=30, null=True, blank=True)
    birth_date = models.DateField(null=True, blank=True)
    phone_number = PhoneNumberField(default='+10000000000')
    gender = models.CharField(max_length=32, choices=[(tag.name, tag.value) for tag in GenderChoice], default=GenderChoice.UNSPECIFIED.value)

    objects = UserManager()
    EMAIL_FIELD = 'email'
    USERNAME_FIELD = 'username'
    REQUIRED_FIELDS = ['email']
    class Meta:
        ordering = ['username']
        verbose_name = _('user')
        verbose_name_plural = _('users')

和

class Message(AbstractIP):
    subject = models.CharField(_('Subject'), max_length=120, blank=True)
    body = models.TextField(_('Body')) # Do we want to cap length or enforce non-blank?
    sender = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='sender_messages', verbose_name=_('Sender'), on_delete=models.CASCADE)
    recipient = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='receiver_messages', verbose_name=_('Recipient'), blank=True, on_delete=models.CASCADE)
    parent_msg = models.ForeignKey('self', related_name='next_messages', null=True, blank=True, verbose_name=_('Parent message'), on_delete=models.CASCADE)
    sent_at = models.DateTimeField(_('sent at'), null=True, blank=True)
    read_at = models.DateTimeField(_('read at'), null=True, blank=True)
    replied_at = models.DateTimeField(_('replied at'), null=True, blank=True)
    sender_deleted_at = models.DateTimeField(_('Sender deleted at'), null=True, blank=True)
    recipient_deleted_at = models.DateTimeField(_('Recipient deleted at'), null=True, blank=True)
    ip = models.GenericIPAddressField(verbose_name=_('IP'), null=True, blank=True)
    user_agent = models.CharField(verbose_name=_('User Agent'), blank=True, max_length=255)

    objects = MessageManager() # Manager for Message queries

    def new(self):
        """Returns whether the recipient has read the message or not"""
        if self.read_at is not None:
            return False
        return True

    def replied(self):
        """Returns whether the recipient has written a reply to this message"""
        if self.replied_at is not None:
            return True
        return False

    def __str__(self):
        if self.subject is not None:
            return self.subject
        if self.body is not None:
            return self.body[:40]
        return None

    def get_absolute_url(self):
        return reverse('messages_detail', args=[self.id])

    def save(self, **kwargs):
        if not self.id:
            self.sent_at = timezone.now()
        super(Message, self).save(**kwargs)

    class Meta:
        ordering = ['-sent_at']
        verbose_name = _('Message')
        verbose_name_plural = _('Messages')

我希望能够执行的查询等同于此，但我无法弄清楚如何在 ORM 中执行此操作，其中 %s 是给定用户的 CustomUser.id (pk) 字段的占位符。

SELECT webrtc_customuser.*
      ,MAX(webrtc_message.sent_at) AS sent_at
      ,MAX(CASE WHEN webrtc_message.read_at IS NULL AND webrtc_customuser.id <> webrtc_message.sender_id THEN 1 ELSE 0 END) AS has_unread
FROM webrtc_customuser
INNER JOIN webrtc_message
  ON (
    webrtc_customuser.id = webrtc_message.sender_id
    AND webrtc_message.sender_id = %s
    AND webrtc_message.sender_deleted_at IS NULL
  ) OR (
    webrtc_customuser.id = webrtc_message.recipient_id
    AND webrtc_message.recipient_id = %s
    AND webrtc_message.recipient_deleted_at IS NULL
  )

我设法通过以下查询获得了正确的 user_id 和派生字段，但无法弄清楚如何让 CustomUser 属性与它们一起加入。

messages = self.values(
    user_fk=Case(When(sender=user, then='recipient'), default='sender', output_field=models.IntegerField())
).exclude(
    sender=user, recipient=user
).filter(
    Q(sender=user, sender_deleted_at__isnull=True) |
    Q(recipient=user, recipient_deleted_at__isnull=True)
).annotate(
    max_sent_at=Max('sent_at'),
    has_unread=Max(Case(When(~Q(sender=user) & Q(read_at__isnull=True), then=1), default=0, output_field=models.IntegerField()))
).order_by()

提前感谢您的宝贵时间！

编辑：更新的 ORM 查询

标签： pythondjangodjango-orm

解决方案

您需要单独指定所需的用户属性：

messages = self.values(
    user_email=Case(When(sender=user, then='recipient__email'), default='sender__email'),
    user_username=Case(When(sender=user, then='recipient__username'), default='sender__username'),
)

不是很漂亮，特别是因为您必须为每一列重复该CASE语句，甚至可能需要为每一列指定output_field一个。

为了解决这个问题，即。要获取所有用户属性而不一一选择它们，您需要 a) 选择CustomUser.object（弄清楚如何选择相关用户并获取相关注释），或 b) 选择完整的消息对象而不仅仅是values()字典. 然后您可以通过message.sender和访问完整的用户对象message.recipient。但在这里，挑战将是如何messages使用子查询过滤和注释查询集，因为只是省略values()会破坏注释中的聚合，因为每个消息对象都是唯一的。

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