Django，使用"|":表达式树太大(最大深度为1000) [英] Django, using "|": Expression tree is too large (maximum depth 1000)

问题描述

我正在尝试将许多查询集连接在一起.我从这个提了一段时间的问题，但这在我的情况下不起作用.我需要返回一个 queryset 而不是一个列表.因此，我使用了第二个答案中的 | .当时效果不错，但是现在我尝试将其再次用于其他用途，但出现以下错误:

 表达式树太大(最大深度为1000) 

我本来以为 | 会合并查询集，但是在阅读文档后，它似乎会合并实际的查询.如果查询变得太长/太复杂，就会发生此特定问题.

这就是我想要做的:

  def属性(自身，请求，pk =无):项目= self.get_object()如果项目为None:return Response({'detail':'Missing project id'}，status = 404)功能= Function.objects.filter(project = project)属性= Property.objects.none()对于功能中的功能:属性=属性|function.property_set.all()返回响应([属性中x的PropertySerializer(x).data]) 

由于 function 查询返回大约1200个结果，并且每个 function 具有大约5个属性，因此我可以理解查询太长/太复杂了.

如何防止查询变得过于复杂?或者我该如何执行多个查询并在以后合并它们，同时将最终结果保留为一个查询集?

解决方案

我想您想获取所有具有 Function 某个项目的 Property 对象./p>

我们可以通过以下方式对此进行查询:

  properties = Property.objects.filter(function__project = project) 

因此，这是一个查询集，其中包含 function (我假设这是 ForeignKey )具有作为 project 的所有属性对象(可能又是 ForeignKey 是给定的 project ).这也将导致单个查询，但是您将避免构造巨大的联合.

或者，您可以分两步执行此操作，但这实际上会使它变慢:

 #效率可能较低function_ids =(Function.objects.filter(project = project).values_list('pk'，flat = True))properties = Properties.object(function_id__in = function_ids) 

I'm trying to concatenate many querysets together. I tried out the marked answer from this question a while back, but that didn't work in my case. I needed to return a queryset not a list. So I used the |, from the second answer. This worked fine at the time, but now that I'm trying to use it again for something else I get the following error:

Expression tree is too large (maximum depth 1000)

I originally thought that | would concat the querysets, but after reading the docs it appears that it concats the actual query. And that this specific problem occurs if the query becomes too long/complex.

This is what I'm trying to do:

def properties(self, request, pk=None):
    project = self.get_object()
    if project is None:
        return Response({'detail': 'Missing project id'}, status=404)

    functions = Function.objects.filter(project=project)
    properties = Property.objects.none()
    for function in functions:
        properties = properties | function.property_set.all()
    return Response([PropertySerializer(x).data for x in properties])

Since the functions query returns roughly 1200 results, and each function has about 5 properties, I can understand the query becoming too long/complex.

How can I prevent the query from becoming too complex? Or how can I execute multiple queries and concat them afterwards, while keeping the end result a queryset?

解决方案

I think you want to obtain all the Property objects that have as Function a certain project.

We can query this with:

properties = Property.objects.filter(function__project=project)

This thus is a queryset that contains all property objects for which the function (I assume this is a ForeignKey) has as project (probably again a ForeignKey is the given project). This will result in a single query as well, but you will avoid constructing gigantic unions.

Alternatively, you can do it in two steps, but this would actually make it slower:

# probably less efficient
function_ids = (Function.objects.filter(project=project)
                                .values_list('pk', flat=True))
properties = Properties.object(function_id__in=function_ids)

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