Re: Feature request: ForeignKey through parameter

2010-10-28 Thread Adrian Holovaty 
On Thu, Oct 28, 2010 at 2:54 AM, Roald de Vries  wrote:
> I quite often reference foreign keys of foreign keys of foreign keys...
> Wouldn't it be nice to have a 'through'-parameter for ForeignKey's?
>
>    class A(Model):
>        b = ForeignKey('B')
>        c = ForeignKey('C', through='B', related_name='a_set')
>
>    class B(Model):
>        c = ForeignKey('C')
>
>
> The advantages of a field A.c wrt a property A.c:
> - it creates a reverse relation, so C.a_set becomes available
> - c becomes queryable: A.objects.filter(c=x)

Hi Roald,

Thanks for suggesting this. I don't think it's worth implementing,
though, because you can already query across multiple foreign-key
relationships like this:

A.objects.filter(b__c__exact=x)

As for making C.a_set available, I'd suggest just doing
A.objects.filter(b__c__exact=c_instance) in your view, and that'll get
the job done.

Adrian

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Re: Feature request: ForeignKey through parameter

2010-10-28 Thread Javier Guerra Giraldez 
On Thu, Oct 28, 2010 at 9:15 AM, Roald de Vries  wrote:
> On first sight, I think I agree with you that the syntax is cleaner like
> this, but I would choose for the through-parameter because it's more
> consistent with the use of the through-parameter for ManyToManyField.

but what if B has more than one ForeignKey('C') fields?

-- 
Javier

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Re: Feature request: ForeignKey through parameter

2010-10-28 Thread Roald de Vries 

On Oct 28, 2010, at 4:02 PM, Javier Guerra Giraldez wrote:
On Thu, Oct 28, 2010 at 2:54 AM, Roald de Vries   
wrote:
I quite often reference foreign keys of foreign keys of foreign  
keys...

Wouldn't it be nice to have a 'through'-parameter for ForeignKey's?


   class A(Model):
   b = ForeignKey('B')
   c = ForeignKey('C', through='B', related_name='a_set')

   class B(Model):
   c = ForeignKey('C')


i'd love such a feature too, but i think a better syntax could be
something like:

  class A(Model):
  b = ForeignKey('B')
  c = ForeignKey('B__c', related_name='a_set')

  class B(Model):
  c = ForeignKey('C')

where the second part of the reference is the name of the field ('c'
in this example), not the model class ('C')


On first sight, I think I agree with you that the syntax is cleaner  
like this, but I would choose for the through-parameter because it's  
more consistent with the use of the through-parameter for  
ManyToManyField.


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Re: Feature request: ForeignKey through parameter

2010-10-28 Thread Javier Guerra Giraldez 
On Thu, Oct 28, 2010 at 2:54 AM, Roald de Vries  wrote:
> I quite often reference foreign keys of foreign keys of foreign keys...
> Wouldn't it be nice to have a 'through'-parameter for ForeignKey's?
>
>
>    class A(Model):
>        b = ForeignKey('B')
>        c = ForeignKey('C', through='B', related_name='a_set')
>
>    class B(Model):
>        c = ForeignKey('C')

i'd love such a feature too, but i think a better syntax could be
something like:

   class A(Model):
   b = ForeignKey('B')
   c = ForeignKey('B__c', related_name='a_set')

   class B(Model):
   c = ForeignKey('C')

where the second part of the reference is the name of the field ('c'
in this example), not the model class ('C')

-- 
Javier

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