def get_by_model(self, queryset_or_model, tags):
"""
Create a ``QuerySet`` containing instances of the specified
model associated with a given tag or list of tags.
"""
tags = get_tag_list(tags)
tag_count = len(tags)
queryset, model = get_queryset_and_model(queryset_or_model)
if tag_count == 0:
return model._default_manager.none()
elif tag_count == 1:
# Optimisation for single tag - fall through to the simpler
# query below.
tag = tags[0]
else:
return self.get_intersection_by_model(queryset_or_model, tags)
content_type = ContentType.objects.get_for_model(model)
opts = self.model._meta
tagged_item_table = qn(opts.db_table)
return queryset.active().extra(
tables=[opts.db_table],
where=[
'%s.content_type_id = %%s' % tagged_item_table,
'%s.tag_id = %%s' % tagged_item_table,
'%s.%s = %s.object_id' % (qn(model._meta.db_table),
qn(model._meta.pk.column),
tagged_item_table)
],
params=[content_type.pk, tag.pk],
)
def get_intersection_by_model(self, queryset_or_model, tags):
"""
Create a ``QuerySet`` containing instances of the specified
model associated with *all* of the given list of tags.
"""
tags = get_tag_list(tags)
tag_count = len(tags)
queryset, model = get_queryset_and_model(queryset_or_model)
if not tag_count:
return model._default_manager.none()
model_table = qn(model._meta.db_table)
# This query selects the ids of all objects which have all the
# given tags.
query = """
SELECT %(model_pk)s
FROM %(model)s, %(tagged_item)s
WHERE %(tagged_item)s.content_type_id = %(content_type_id)s
AND %(tagged_item)s.tag_id IN (%(tag_id_placeholders)s)
AND %(model_pk)s = %(tagged_item)s.object_id
GROUP BY %(model_pk)s
HAVING COUNT(%(model_pk)s) = %(tag_count)s""" % {
'model_pk': '%s.%s' % (model_table, qn(model._meta.pk.column)),
'model': model_table,
'tagged_item': qn(self.model._meta.db_table),
'content_type_id': ContentType.objects.get_for_model(model).pk,
'tag_id_placeholders': ','.join(['%s'] * tag_count),
'tag_count': tag_count,
}
cursor = connection.cursor()
cursor.execute(query, [tag.pk for tag in tags])
object_ids = [row[0] for row in cursor.fetchall()]
if len(object_ids) > 0:
return queryset.filter(pk__in=object_ids)
else:
return model._default_manager.none()
