diff -r 65c9d8baf7d0 -r f257ad33bed5 src/cm/models.py
--- a/src/cm/models.py	Wed Jan 27 15:01:51 2010 +0100
+++ b/src/cm/models.py	Wed Jan 27 16:18:30 2010 +0100
@@ -264,10 +264,15 @@
         comment.save(keep_dates=keep_dates)
         return comment
     
+from cm.models_base import KEY_MAX_SIZE, generate_key
+
 class Comment(PermanentModel, AuthorModel):
     modified = models.DateTimeField()
     created = models.DateTimeField()
 
+    # key to identify same comments across versions
+    id_key = models.CharField(max_length=KEY_MAX_SIZE, db_index=True, default=generate_key)
+
     text_version = models.ForeignKey("TextVersion")
 
     # comment_set will be replies