def generic_annotate(qs_model,
generic_qs_model,
aggregator,
gfk_field=None,
alias='score'):
"""
Find blog entries with the most comments:
qs = generic_annotate(Entry.objects.public(), Comment.objects.public(), Count('comments__id'))
for entry in qs:
print entry.title, entry.score
Find the highest rated foods:
generic_annotate(Food, Rating, Avg('ratings__rating'), alias='avg')
for food in qs:
print food.name, '- average rating:', food.avg
.. note::
In both of the above examples it is assumed that a GenericRelation exists
on Entry to Comment (named "comments") and also on Food to Rating (named "ratings").
If a GenericRelation does *not* exist, the query will still return correct
results but the code path will be different as it will use the fallback method.
.. warning::
If the underlying column type differs between the qs_model's primary
key and the generic_qs_model's foreign key column, it will use the fallback
method, which can correctly CASTself.
:param qs_model: A model or a queryset of objects you want to perform
annotation on, e.g. blog entries
:param generic_qs_model: A model or queryset containing a GFK, e.g. comments
:param aggregator: an aggregation, from django.db.models, e.g. Count('id') or Avg('rating')
:param gfk_field: explicitly specify the field w/the gfk
:param alias: attribute name to use for annotation
"""
prepared_query = prepare_query(qs_model, generic_qs_model, aggregator,
gfk_field)
if prepared_query is not False:
return prepared_query.annotate(**{alias: aggregator})
else:
# need to fall back since CAST will be missing
return fallback_generic_annotate(qs_model, generic_qs_model,
aggregator, gfk_field, alias)
def generic_annotate(qs_model, generic_qs_model, aggregator, gfk_field=None, alias="score"):
"""
Find blog entries with the most comments:
qs = generic_annotate(Entry.objects.public(), Comment.objects.public(), Count('comments__id'))
for entry in qs:
print entry.title, entry.score
Find the highest rated foods:
generic_annotate(Food, Rating, Avg('ratings__rating'), alias='avg')
for food in qs:
print food.name, '- average rating:', food.avg
.. note::
In both of the above examples it is assumed that a GenericRelation exists
on Entry to Comment (named "comments") and also on Food to Rating (named "ratings").
If a GenericRelation does *not* exist, the query will still return correct
results but the code path will be different as it will use the fallback method.
.. warning::
If the underlying column type differs between the qs_model's primary
key and the generic_qs_model's foreign key column, it will use the fallback
method, which can correctly CASTself.
:param qs_model: A model or a queryset of objects you want to perform
annotation on, e.g. blog entries
:param generic_qs_model: A model or queryset containing a GFK, e.g. comments
:param aggregator: an aggregation, from django.db.models, e.g. Count('id') or Avg('rating')
:param gfk_field: explicitly specify the field w/the gfk
:param alias: attribute name to use for annotation
"""
prepared_query = prepare_query(qs_model, generic_qs_model, aggregator, gfk_field)
if prepared_query is not False:
return prepared_query.annotate(**{alias: aggregator})
else:
# need to fall back since CAST will be missing
return fallback_generic_annotate(qs_model, generic_qs_model, aggregator, gfk_field, alias)
def generic_aggregate(self, *args, **kwargs):
return fallback_generic_annotate(*args, **kwargs)
def generic_aggregate(self, *args, **kwargs):
return fallback_generic_annotate(*args, **kwargs)