2 files changed, 32 insertions, 7 deletions
diff --git a/db.py b/db.py
index df9ceda..e75adca 100644
--- a/db.py
+++ b/db.py
@@ -1,18 +1,40 @@
+from django.db import connections
 from django.db.models import Manager
 from django.db.models.query import QuerySet
+from django.db.models.sql.compiler import SQLCompiler
 from django.db.models.sql.query import Query
+from django.db.models.sql.where import WhereNode
+
+
+class GroupedCompiler(SQLCompiler):
+    def get_group_by(self, select, order_by):
+        result = super(GroupedCompiler, self).get_group_by(select, order_by)
+        expressions = []
+        for expr in self.query.real_group_by:
+            ref = expr if hasattr(expr, "as_sql") else self.query.resolve_ref(expr)
+            sql, params = self.compile(ref)
+            result.append((sql, params))
+
+        return result
 
 
 class GroupedQuery(Query):
-    def add_grouping(self, *grouping):
-        if self.group_by is None:
-            self.group_by = []
+    def __init__(self, model, where=WhereNode):
+        super(GroupedQuery, self).__init__(model, where)
+        self.real_group_by = []
 
-        if isinstance(self.group_by, list):
-            self.group_by.extend(grouping)
+    def add_grouping(self, *grouping):
+        self.real_group_by.extend(grouping)
 
     def clear_grouping(self):
-        self.group_by = None
+        self.real_group_by = []
+
+    def get_compiler(self, using=None, connection=None):
+        if using is None and connection is None:
+            raise ValueError("Need either using or connection")
+        if using:
+            connection = connections[using]
+        return GroupedCompiler(self, connection, using)
 
 
 class GroupedQuerySet(QuerySet):
diff --git a/models.py b/models.py
index 64fb675..26bb63d 100644
--- a/models.py
+++ b/models.py
@@ -4,6 +4,8 @@ from django.db.models.expressions import RawSQL
 from django.db.models.functions import Extract, ExtractYear
 from django.utils.text import slugify
 
+from .db import GroupedManager
+
 import hashlib
 import os
 
@@ -111,7 +113,7 @@ class Room(models.Model):
         verbose_name_plural = "salles"
 
 
-class CourseManager(models.Manager):
+class CourseManager(GroupedManager):
     def __get_weeks(self, qs):
         extractYear = ExtractYear("begin")
 
@@ -130,6 +132,7 @@ class CourseManager(models.Manager):
         qs = self.get_courses_for_group(group, **filters)
         return self.__get_weeks(qs)
 
+
 class Course(models.Model):
     objects = CourseManager()