基本上我遇到的问题是：我需要一个选项或替代方法来过滤联合查询集上的注释字段。
我有以下简化模型设置：
class Course(Model):
groups = ManyToManyField(through=CourseAssignment)
class CourseAssignment(Model):
course = ForeignKey(Course)
group = ForeignKey(Group)
teacher = ForeignKey(Teacher)
class Lesson(Model):
course = ForeignKey(Course, related_name='lessons')
class AssignmentProgress(Model):
lesson = ForeignKey(related_name='progresses')
course_assignment = ForeignKey(CourseAssignment)
student = ForeignKey(Student)
group = ForeignKey(Group)
status = CharField(choices=(
('on_check', 'On check'),
('complete', 'Complete'),
('assigned', 'Assigned'),
))
deadline = DateTimeField()
checked_date = DateTimeField()
我需要显示按课程分组的作业进度统计数据和分配课程的组。这是我的初始查询集，请注意课程在最终结果中重复，不同之处在于带注释的数据：
def annotated_lessons_queryset():
lessons = None
for course_assignment in CourseAssignment.objects.all():
qs = Lesson.objects.filter(
course=course_assignment.course
).annotate(
completed_progresses=Count(
'progresses',
filter=Q(group=course_assignment.group),
output_field=IntegerField()
),
on_check=Exists(
AssignmentProgress.objects.filter(
lesson=OuterRef('id'), group=course_assignment.group, status='on_check'
)
)
)
lessons = qs if lessons is None else lessons.union(qs)
return lessons
我佳能使用| 此处为 OR 运算符，因为它仅返回不同的课程值。到目前为止，这一直有效，直到我尝试过滤所有带有注释状态 on_check 的课程：
qs = annotated_lessons_queryset().filter(on_check=True)
失败并出现错误：
raise NotSupportedError(
django.db.utils.NotSupportedError: Calling QuerySet.filter() after union() is not supported.
请提出解决方法或其他方法来过滤此查询集。