Simple Djanqo Query generating confusing Queryset results

问题

[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?

回答1:

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.

来源：https://stackoverflow.com/questions/7843687/simple-djanqo-query-generating-confusing-queryset-results