使用相关表中的值对django QuerySet进行注释 [英] Annotating django QuerySet with values from related table

问题描述

我有一个模型页与2个相关模型PageScoreHistory和PageImageHistory，其中两个历史模型都有页面字段作为ForeignKey到页面并且有一个日期字段。我遇到的问题是，当我收到一个PageImageHistory QuerySet的列表时，我想能够检索页面在拍摄图像时的分数。对于一个单独的PageImageHistory对象，我可以轻松地这样做：

  pih = PageImageHistory.objects.get（id = 123）
 score = pih.page.pagescorehistory_set.filter（datetime__lte = pih.captured）.latest（'datetime'）
  

但是对于QuerySet，我想避免为集合中的每个成员运行查询。有没有办法这样做是一个理智的方式，没有实际循环遍历集合的所有成员？

解决方案

没有看到你的模型，但这是否做你想要的？

  PageImageHistory.objects.filter（
 page__pagescorehistory__datetime__lte = x。捕获
）.annotate（Max（'page__pagescorehistory__datetime'）
  

I have a model Page with 2 related models PageScoreHistory and PageImageHistory, where both history models have page field as a ForeignKey to Page and have a date field. The problem I am having, is that when I get a list of PageImageHistory QuerySet, I want to be able to retrieve the score the page had at the time the image was taken. For an individual PageImageHistory object, I can do this easily:

pih = PageImageHistory.objects.get(id=123)
score = pih.page.pagescorehistory_set.filter(datetime__lte=pih.captured).latest('datetime')

But for a QuerySet, I would like to avoid running a query for each member of the set. Is there a wayo to do this is a sane fashion, without actually looping through all members of the set?

解决方案

It's hard without seeing your models, but does this do what you want?

PageImageHistory.objects.filter(
    page__pagescorehistory__datetime__lte=x.captured
).annotate(Max('page__pagescorehistory__datetime')

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