I think you misunderstand: I am not actually tracking llama herds. :-) This is just example code; I haven't actually tested it in the way that you suggest. The problem isn't with this code in particular, it's with this concept in general. This is a question I have had again and again in the past few years - this code is just a way to articulate it.
So, in short - no, the code won't work as now written, and it's obvious why: annotate doesn't assign instances, it assigns results. I don't think I need an annotation expert per se; it may well be that annotate is the wrong way to do this. My SQL isn't particularly strong, but if I were writing this in SQL, I suspect that GROUP_BY is necessary or at least plausible. I know that Django doesn't directly expose GROUP_BY, but it looks likes QuerySet.values() uses it; so I wonder if that fits into the picture somehow? On Wed, Apr 2, 2014 at 12:35 PM, Bill Freeman <ke1g...@gmail.com> wrote: > My point was that annotate might work after the other problems were > fixed. Have you re-tested since? If your annotate still doesn't work then > perhaps someone with more annotate experience than I will comment. > > > > On Wed, Apr 2, 2014 at 12:04 PM, Justin Holmes <jus...@justinholmes.com>wrote: > >> No no, the annotate doesn't work - that's the whole reason for my >> question. See, the annotate doesn't associate instances with the annotated >> attribute, it associated results. >> >> (BTW, good looking out - I have once again fixed the SO question :-)) >> >> >> On Wed, Apr 2, 2014 at 10:17 AM, Bill Freeman <ke1g...@gmail.com> wrote: >> >>> 1. You now have a foreign key to Herd, but you don't have a model by >>> that name. It's called LlamaHerd. >>> >>> 2. I was misinterpreting what you wanted (couldn't get past the lack of >>> a relationship while reading0. Once the relationship is fixed, your >>> original annotate might work. >>> >>> >>> On Tue, Apr 1, 2014 at 6:20 PM, Justin Holmes >>> <jus...@justinholmes.com>wrote: >>> >>>> You say "use the reverse relation manager in LlamaHerd to build up your >>>> annotation," but that answer the question. >>>> >>>> How can I sort LlamaHerd objects by the DOB of their largest llama? >>>> >>>> >>>> On Tue, Apr 1, 2014 at 6:13 PM, Justin Holmes >>>> <jus...@justinholmes.com>wrote: >>>> >>>>> 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...@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 < >>>>>> jus...@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. >>>>>>> >>>>>>> >>>>>>> -- >>>>>>> Justin Holmes >>>>>>> Chief Chocobo Breeder, slashRoot >>>>>>> >>>>>>> slashRoot: Coffee House and Tech Dojo >>>>>>> New Paltz, NY 12561 >>>>>>> 845.633.8330 >>>>>>> >>>>>>> -- >>>>>>> You received this message because you are subscribed to the Google >>>>>>> Groups "Django users" group. >>>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>>> send an email to django-users+unsubscr...@googlegroups.com. >>>>>>> To post to this group, send email to django-users@googlegroups.com. >>>>>>> Visit this group at http://groups.google.com/group/django-users. >>>>>>> To view this discussion on the web visit >>>>>>> https://groups.google.com/d/msgid/django-users/CAMGywB6gkBvhFs%2BP2PrtDah24VDCko8QK-1UCnSGugz_ts1v8g%40mail.gmail.com<https://groups.google.com/d/msgid/django-users/CAMGywB6gkBvhFs%2BP2PrtDah24VDCko8QK-1UCnSGugz_ts1v8g%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>>>>> . >>>>>>> For more options, visit https://groups.google.com/d/optout. >>>>>>> >>>>>> >>>>>> -- >>>>>> You received this message because you are subscribed to the Google >>>>>> Groups "Django users" group. >>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>> send an email to django-users+unsubscr...@googlegroups.com. >>>>>> To post to this group, send email to django-users@googlegroups.com. >>>>>> Visit this group at http://groups.google.com/group/django-users. >>>>>> To view this discussion on the web visit >>>>>> https://groups.google.com/d/msgid/django-users/CAB%2BAj0srKNzRs%3DzbsPm%2BobxLNFCcjRccGSVeYykF1PSnJc-ydQ%40mail.gmail.com<https://groups.google.com/d/msgid/django-users/CAB%2BAj0srKNzRs%3DzbsPm%2BobxLNFCcjRccGSVeYykF1PSnJc-ydQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>>>> . >>>>>> For more options, visit https://groups.google.com/d/optout. >>>>>> >>>>> >>>>> >>>>> >>>>> -- >>>>> Justin Holmes >>>>> Chief Chocobo Breeder, slashRoot >>>>> >>>>> slashRoot: Coffee House and Tech Dojo >>>>> New Paltz, NY 12561 >>>>> 845.633.8330 >>>>> >>>> >>>> >>>> >>>> -- >>>> Justin Holmes >>>> Chief Chocobo Breeder, slashRoot >>>> >>>> slashRoot: Coffee House and Tech Dojo >>>> New Paltz, NY 12561 >>>> 845.633.8330 >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "Django users" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to django-users+unsubscr...@googlegroups.com. >>>> To post to this group, send email to django-users@googlegroups.com. >>>> Visit this group at http://groups.google.com/group/django-users. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/django-users/CAMGywB4V3zpbqr7v1kcvOi8%2BoqLPm0nr18dGStaedys494%2BOag%40mail.gmail.com<https://groups.google.com/d/msgid/django-users/CAMGywB4V3zpbqr7v1kcvOi8%2BoqLPm0nr18dGStaedys494%2BOag%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Django users" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to django-users+unsubscr...@googlegroups.com. >>> To post to this group, send email to django-users@googlegroups.com. >>> Visit this group at http://groups.google.com/group/django-users. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/django-users/CAB%2BAj0vE%2Bc8feae_j8v5_U9UHod1RaphytQQASXD1Dwq4RBGDw%40mail.gmail.com<https://groups.google.com/d/msgid/django-users/CAB%2BAj0vE%2Bc8feae_j8v5_U9UHod1RaphytQQASXD1Dwq4RBGDw%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> >> >> -- >> Justin Holmes >> Chief Chocobo Breeder, slashRoot >> >> slashRoot: Coffee House and Tech Dojo >> New Paltz, NY 12561 >> 845.633.8330 >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Django users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to django-users+unsubscr...@googlegroups.com. >> To post to this group, send email to django-users@googlegroups.com. >> Visit this group at http://groups.google.com/group/django-users. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/django-users/CAMGywB4mV1%3DFBeECvwOYP3o-ksm_KNN4s6NX7TpCbVCv70h%2BzQ%40mail.gmail.com<https://groups.google.com/d/msgid/django-users/CAMGywB4mV1%3DFBeECvwOYP3o-ksm_KNN4s6NX7TpCbVCv70h%2BzQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> For more options, visit https://groups.google.com/d/optout. >> > > -- > You received this message because you are subscribed to the Google Groups > "Django users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to django-users+unsubscr...@googlegroups.com. > To post to this group, send email to django-users@googlegroups.com. > Visit this group at http://groups.google.com/group/django-users. > To view this discussion on the web visit > https://groups.google.com/d/msgid/django-users/CAB%2BAj0tjx%3Dvf3R5T-COATEXF%2BchmUNXiP1vN0HWiMzC7Ws-aYQ%40mail.gmail.com<https://groups.google.com/d/msgid/django-users/CAB%2BAj0tjx%3Dvf3R5T-COATEXF%2BchmUNXiP1vN0HWiMzC7Ws-aYQ%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- Justin Holmes Chief Chocobo Breeder, slashRoot slashRoot: Coffee House and Tech Dojo New Paltz, NY 12561 845.633.8330 -- You received this message because you are subscribed to the Google Groups "Django users" group. 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