Django 通过对两个字段的查询进行不同的分组 [英] Django distinct group by query on two fields

问题描述

我有一个有 2 个字段的模型.

I have a model which have 2 fields.

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

现在这个模型可以有多行具有相同的tcode，并且每一行可以有不同的日期或相同.

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.

我想过滤此模型上的查询，以便 tcode 和日期字段组合应该是唯一的.我怎样才能得到所有这些对象.

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，如果两个字段中有两行数据相同，我想要哪一行！对我来说无关紧要，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

我认为没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，则可以这样做:

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()

这不会为您提供完整的 MyModel 对象，而是包含 tcode 和 created_on 的所有现有组合的字典列表.

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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