在Django中执行两个带注释值的总和

Question

我在Student对象上做了注释，因此它有两个新字段 - ＆gt; project_count和member_count如下：

top_students = Student.objects.annotate(project_count= Count('project'), member_count = Count('member_student'))

我现在想在数据库级别执行这两个值的总和。返回类似的东西：

total_count = project_count + member_count

我尝试过像这样使用.extra（）：

top_students = Student.objects.annotate(project_count= Count('project'), member_count = Count('member_student')).extra( select = {'total_count': 'project_count + member_count'}, order_by = ('total_count', ) )

但它显示错误：OperationalError: (1054, "Unknown column 'project_count' in 'field list'")

我应该编写原始SQL还是有其他方法来执行此操作：