Re: ORM Question

Yes, absolutely - my bad.  I have updated to SO question.  I meant the models to look like:

class LlamaHerd(models.Model):      shepherd = ForeignKey(User)    class Llama(models.Model):      size = FloatField()      dob = FloatField      herd = ForeignKey(Herd, related_name="llamas")

On Tue, Apr 1, 2014 at 6:09 PM, Bill Freeman <ke1g.nh@gmail.com> wrote:

Aren't you missing a ForeignKey relationship to tell which LlamaHerd a Llama belongs to?

Then you would use the reverse relation manager in LlamaHerd to build up your annotation.

On Tue, Apr 1, 2014 at 5:52 PM, Justin Holmes <justin@justinholmes.com> wrote:

I have come across this problem in several Django projects, but only just now worked it out in my head enough to make it a cognizable question.

I have also posted it on StackOverflow, here: http://stackoverflow.com/questions/22797497/using-the-django-orm-to-order-by-a-value-in-a-distinct-related-item

Consider this example:

class LlamaHerd(models.Model):      shepherd = ForeignKey(User)    class Llama(models.Model):      size = FloatField()      dob = FloatField

How can I now make a query to get LlamaHerd objects, sorted by the date of birth of their largest llama?

It almost feels like I might be able to use annotate:

LlamaHerd.annotate(largest_llama=Max('llama__size')).order_by('largest_llama__dob')

...but the annotate here creates fields with float values, not with the model instances.

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