revision compare for course articles

Course/admin.py

@@ -1,12 +1,31 @@
 from django.contrib import admin
 from mptt.admin import DraggableMPTTAdmin
 from .models import Course, Topics, Links, TopicArticle
+from reversion_compare.admin import CompareVersionAdmin
+from reversion_compare.mixins import CompareMixin
+from django.db.models import Manager
 # Register your models here.
 
+_old_compare = CompareMixin.compare
+
+
+def compare(self, obj, version1, version2):
+    def replace_taggit_field(version_ins):
+        for fieldname in version_ins.field_dict:
+            if isinstance(version_ins.field_dict[fieldname], Manager):
+                version_ins.field_dict[fieldname] = []
+    replace_taggit_field(version1)
+    replace_taggit_field(version2)
+    return _old_compare(self, obj, version1, version2)
+
+CompareMixin.compare = compare
+
+class TopicArticleAdmin(CompareVersionAdmin):
+    pass
 
 admin.site.register(Course)
 admin.site.register(Links)
-admin.site.register(TopicArticle)
+admin.site.register(TopicArticle, TopicArticleAdmin)