On Tue, Feb 10, 2009 at 8:43 PM, Alessandro <alessandro.ron...@gmail.com> wrote:
>
>
> 2009/2/10 Russell Keith-Magee <freakboy3...@gmail.com>
>>
>>
>> However, if you're using Django trunk, what you want is:
>>
>> >>> from django.db.models import Max
>> >>> qs =
>> >>> Module_scheme.objects.filter(plant=3).annotate(max_energy_tot=Max('module__energy_tot'))
>> >>> for mod in qs:
>> ... print mod.id, mod.max_energy_tot
>>
>> That is - retrieve a list of Module_scheme objects associated with
>> plant 3, and annotate each one of which is annotated with the maximum
>> of the energy_tot of the modules related to the Module_scheme. The
>> maximum is provided as an extra attribute on each of the Module_scheme
>> instance.
>
> I cannot do this because I have a ForeignKey from Module to Module_Scheme,
> and your first line returns
>
> FieldError: Cannot resolve keyword 'module' into field. Choices are: id,
> jbox, module_number, modules, plant, rack_number
Apologies - I misread the name of your class. The query should read:
Module_scheme.objects.filter(plant=3).annotate(max_energy_tot=Max('modules__energy_tot'))
i.e., plural modules, not singular module, in the Max lookup. It's the
reverse lookup name for the module relationship on Module_scheme. For
future reference, the message on the FieldError tells you the right
name - modules.
Yours,
Russ Magee %-)
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