如何通过多对多字段中的对象过滤Django模型(完全匹配)?

问题描述

我的代码中有这个模型:

I have this model in my code:

class Conversation(models.Model):
    participants = models.ManyToManyField(User, related_name="message_participants")

，我需要通过参与者"多对多字段过滤此对话"模型对象.含义:例如，我有3个User对象，因此我想检索在参与者"字段中具有这3个User的唯一"Conversation"对象.

and I need to filter this "Conversation" model objects by the "participants" many-to-many field.meaning: I have for example 3 User objects, so I want to retrieve the only "Conversation" objects that has this 3 Users in it's "participants" field.

我尝试这样做:

def get_exist_conv_or_none(sender,recipients):
    conv = Conversation.objects.filter(participants=sender)
    for rec in recipients:
        conv = conv.filter(participants=rec)

其中，发件人是用户对象，收件人"是用户对象的列表.它不会引发错误，但是会给我错误的对话对象.谢谢.

where sender is a User object and "recipients" is a list of User objects.it won't raise error but it gives me the wrong Object of Conversation.Thanks.

最近的尝试使我想到了这一点:

edit:A more recent try lead me to this:

def get_exist_conv_or_none(sender,recipients):
    participants=recipients
    participants.append(sender)
    conv = Conversation.objects.filter(participants__in=participants)
    return conv

基本上有相同的问题.它产生的对象具有列表中一个或多个参与者".但我要寻找的是多对多对象的精确匹配.意思是，对象上具有确切的用户"的多对多关系.

which basically have the same problem. It yields Objects which has one or more of the "participants" on the list. but what Im looking for is exact match of the many-to-many object.Meaning, an Object with the exact "Users" on it's many-to-many relation.

edit 2:我的最后一次尝试.仍然不行.

edit 2: My last attempt. still, won't work.

def get_exist_conv_or_none(sender,recipients):
    recipients.append(sender)
    recipients = list(set(recipients))
    conv = Conversation.objects.annotate(count=Count('participants')).filter(participants=recipients[0])
    for participant in recipients[1:]:
        conv.filter(participants=participant)
    conv.filter(count=len(recipients))
    return conv

推荐答案

好，所以我找到了答案:为了进行精确匹配，我必须对模型进行链式过滤，然后确保模型具有所需的确切参数数量，以便多对多"字段中包含所有 需要的物体，再也没有了.

Ok so I found the answer:In order to make an exact match I have to chain-filter the model and then make sure it has the exact number of arguments it needs to have, so that the many-to-many field will have in it all the objects needed and no more.

我将使用注释检查对象编号:( https://docs.djangoproject.com/en/dev/topics/db/aggregation/)

I will check for the objects number using annotation: ( https://docs.djangoproject.com/en/dev/topics/db/aggregation/ )

最后加上以下代码:

def get_exist_conv_or_none(recipients):
    conv = Conversation.objects.annotate(count=Count('participants')).filter(participants=recipients[0])
    for participant in recipients[1:]:
        conv = conv.filter(participants=participant)
    conv = conv.filter(count=len(recipients))
    return conv

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