gistfile1.diff

diff --git a/taggit/managers.py b/taggit/managers.py
index a751e21..918d256 100644
--- a/taggit/managers.py
+++ b/taggit/managers.py
@@ -2,7 +2,7 @@ from collections import defaultdict
 
 import django
 from django.contrib.contenttypes.models import ContentType
-from django.db import models
+from django.db import models, connection
 from django.db.models.fields.related import ManyToManyRel
 from django.db.models.query_utils import QueryWrapper
 
@@ -175,3 +175,67 @@ class _TaggableManager(models.Manager):
             obj.similar_tags = result["n"]
             results.append(obj)
         return results
+
+    def _get_usage(self, model, counts=False, min_count=None, extra_joins=None, extra_criteria=None, params=None):
+        """
+        Perform the custom SQL query for ``usage_for_model`` and
+        ``usage_for_queryset``.
+        """
+        if min_count is not None: counts = True
+
+        qn = connection.ops.quote_name
+        model_table = qn(model._meta.db_table)
+        model_pk = '%s.%s' % (model_table, qn(model._meta.pk.column))
+        query = """
+        SELECT DISTINCT %(tag)s.id, %(tag)s.name%(count_sql)s
+        FROM
+            %(tag)s
+            INNER JOIN %(tagged_item)s
+                ON %(tag)s.id = %(tagged_item)s.tag_id
+            INNER JOIN %(model)s
+                ON %(tagged_item)s.object_id = %(model_pk)s
+            %%s
+        WHERE %(tagged_item)s.content_type_id = %(content_type_id)s
+            %%s
+        GROUP BY %(tag)s.id, %(tag)s.name
+        %%s
+        ORDER BY %(tag)s.name ASC""" % {
+            'tag': qn(Tag._meta.db_table),
+            'count_sql': counts and (', COUNT(%s)' % model_pk) or '',
+            'tagged_item': qn(TaggedItem._meta.db_table),
+            'model': model_table,
+            'model_pk': model_pk,
+            'content_type_id': ContentType.objects.get_for_model(model).pk,
+        }
+
+        min_count_sql = ''
+        if min_count is not None:
+            min_count_sql = 'HAVING COUNT(%s) >= %%s' % model_pk
+            params.append(min_count)
+
+        cursor = connection.cursor()
+        cursor.execute(query % (extra_joins, extra_criteria, min_count_sql), params)
+        tags = []
+        for row in cursor.fetchall():
+            t = Tag.objects.get(pk=row[0])
+            if counts:
+                t.count = row[2]
+            tags.append(t)
+        return tags
+
+    def filter(self, queryset, counts=False, min_count=None):
+        """
+        Return a list of tags associated with instances of a model
+        contained within a given queryset.
+        """
+        if getattr(queryset.query, 'get_compiler', None):
+            compiler = queryset.query.get_compiler(using='default')
+            extra_joins = ' '.join(compiler.get_from_clause()[0][1:])
+            where, params = queryset.query.where.as_sql(
+                compiler.quote_name_unless_alias, compiler.connection
+            )
+        if where:
+            extra_criteria = 'AND %s' % where
+        else:
+            extra_criteria = ''
+        return self._get_usage(queryset.model, counts, min_count, extra_joins, extra_criteria, params)