Django在两个字段上按查询进行分组

问题描述

我有一个模型，其中有2个字段.

I have a model which have 2 fields.

class MyModel:
   tcode = Charfield
   created_on = Date field
   #some more fields

现在此模型可以有多个具有相同tcode的行，并且每行可以具有不同的日期或相同的日期.

now this model can have multiple rows with same tcode, and each row can have different day or same.

例如

tcode1, 1/2/2001
tcode2, 1/2/2001
tcode2, 2/2/2001
....etc.

我想对此模型进行查询，以便tcode和日期字段组合应该是唯一的.我如何获得所有这些对象.

I want to filter query on this model such that tcode and date field combination should be unique. how can I get all those objects.

我正在尝试这样做

MyModel.objects.all().order_by('tcode').distinct('tcode', 'created_on')

现在，您可能会问，如果在两个字段中有两行具有相同的数据，我想要哪一行！对我来说没关系，任何行都可以正常工作.

Now you may ask that in case if there are two rows with same data in two fields which one row I want! it doesn't matter to me, any row would work fine.

推荐答案

我不认为只有一个查询可以做到这一点，因为数据库中没有机制可以从重复项中随机选择一个.但是，如果您只关心这两个字段，则可以执行以下操作:

I don't think there's one single query that could do this, because there's no mechanism from database to pick random one from duplicates. However, if you only care about those two fields, you could do:

MyModel.objects.order_by('tcode').values('tcode', 'created_on').distinct()

这不会给您完整的MyModel对象，而是一列字典，其中包含tcode和created_on的所有现有组合.

This won't give you complete MyModel objects, but a list of dictionaries that contain all the existing combinations of tcode and created_on.

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