On Apr 10, 2013, at 7:44 AM, bradley griffiths wrote:
> Corss posted from stack overflow
>
> When using the 'in' operator on a queryset, the first time the call is made
> it fails.
>
> from django.db import models
>
>
> class Category(models.Model):
> name = models.CharField(max_length=100)
>
>
> class Project(models.Model):
> categories = models.ManyToManyField(Category, related_name='projects')
>
>
> category_list = Category.objects.prefetch_related('projects')
>
>
> print category_list # [<Category: Category object>, <Category: Category
> object>]
> print category_list[0] in category_list # False
> print category_list[0] in category_list # True
> If I remove 'prefetch_related' and use 'all' instead then the problem is
> gone, however this uses many more DB calls.
>
> How can I get the correct result first time using prefetch_related?
>
You might try converting the QuerySet into a list first. QuerySets avoid
actually caching data for as long as possible.
Peter of the Norse
[email protected]
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