[Django] #27744: Complex prefetch_related broken (from 1.9 to 1.10)

[Django]

#27744: Complex prefetch_related broken (from 1.9 to 1.10)
-------------------------------------+-------------------------------------
               Reporter:  Pascal     |          Owner:  nobody
  Briet                              |
                   Type:  Bug        |         Status:  new
              Component:  Database   |        Version:  1.10
  layer (models, ORM)                |
               Severity:  Normal     |       Keywords:  prefetch
           Triage Stage:             |      Has patch:  0
  Unreviewed                         |
    Needs documentation:  0          |    Needs tests:  0
Patch needs improvement:  0          |  Easy pickings:  0
                  UI/UX:  0          |
-------------------------------------+-------------------------------------
 Was working on : 1.9.10
 Is not working on : 1.10.5

 {{{
 #!div style="font-size: 80%"
   {{{#!python
 from offer.models import Price, PriceGrid
 from django.db.models import Prefetch


 price_queryset = Price.objects.prefetch_related('calculation_rules__rule')

 pricegrids = PriceGrid.objects.all()
 pricegrids = pricegrids.prefetch_related(Prefetch('prices',
 queryset=price_queryset))

 for pg in pricegrids: print(pg.pk)
   }}}
 }}}

 `AttributeError: Cannot find 'rule' on RelatedManager object,
 'prices__calculation_rules__rule' is an invalid parameter to
 prefetch_related()`

 But this still works :


 {{{
 #!div style="font-size: 80%"
   {{{#!python

 pgs =
 PriceGrid.objects.prefetch_related('prices__calculation_rules__rule').all()

 for pg in pgs:
     for price in pg.prices.all():
         for dr in price.calculation_rules.all():
              print(dr.rule.pk)

   }}}
 }}}

 Models (extracts) :

 {{{
 #!div style="font-size: 80%"
   {{{#!python
 class Price(models.Model):
     grid                = models.ForeignKey(PriceGrid,
 related_name="prices")

 class PriceCalculationRule(models.Model):
     price  = models.ForeignKey(Price, on_delete=models.CASCADE,
 related_name="calculation_rules")
     rule   = models.ForeignKey(Rule, on_delete=models.PROTECT,
 verbose_name="Condition")

   }}}
 }}}

--
Ticket URL: <https://code.djangoproject.com/ticket/27744>
Django <https://code.djangoproject.com/>
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