简单的Djanqo查询产生令人困惑的Queryset结果 [英] Simple Djanqo Query generating confusing Queryset results

问题描述

[更新：软件版本Python 2.7.2，Django 1.3.1]

任何人都可以解释这个控制台代码？ >

FinishingStep对引用对象有一个ForeignKey，但并不真正相关。

 >>> fin = FinishingStep.objects.filter（quote = jq）
>>> fin 
 [< FinishingStep：Tabbing>< FinishingStep：Collat​​or>] 
  

非常好，我们已经返回了一个具有两个对象的QuerySet。

但是现在的混乱。这两个对象现在看起来都是一样的：

 >>> fin [0] 
< FinishingStep：Collat​​or> 
>>> fin [1] 
< FinishingStep：Collat​​or> 
  

将其转换为列表，并修复它。

 >>> fin = list（fin）
>>>> fin 
 [< FinishingStep：Tabbing>< FinishingStep：Collat​​or>] 
>>> fin [0] 
< FinishingStep：Tabbing> 
>>> fin [1] 
< FinishingStep：Collat​​or> 
  

[更新：将.distinct（）添加到查询中也会修复它。这个特别奇怪的是，目前在数据库中只有这两个项目。]

这是一个bug吗？我做错了什么？

解决方案

这个机票讨论了这个行为： https://code.djangoproject.com/ticket/9006

只需使用 order_by 查询。这是因为数据库引擎可以自由返回任何合适的行，如果您没有指定明确的排序。所以我想它只是从缓存中挑选一个。

[Update: software versions Python 2.7.2, Django 1.3.1]

Can anyone explain this console code?

FinishingStep has a ForeignKey to a quote object, but that's not really relevant.

>>> fins = FinishingStep.objects.filter(quote=jq)
>>> fins
[<FinishingStep: Tabbing>, <FinishingStep: Collator>]

So far so good, we have returned a QuerySet with two objects.

But now the confusion. Both objects now appear to be the same:

>>> fins[0]
<FinishingStep: Collator>
>>> fins[1]
<FinishingStep: Collator>

Convert it to a list, and that fixes it.

>>> fins = list(fins)
>>> fins
[<FinishingStep: Tabbing>, <FinishingStep: Collator>]
>>> fins[0]
<FinishingStep: Tabbing>
>>> fins[1]
<FinishingStep: Collator>

[Update: Adding .distinct() to the query also fixes it. This especially odd since, at the moment, there are only those two items in the database.]

Is this a bug? Am I doing something wrong?

解决方案

This ticket discusses this behavior: https://code.djangoproject.com/ticket/9006

Just use order_by query. This happens because the database engine is free to return any suitable row if you do not specify explicit ordering. So I guess it just picks the one from its cache.

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