fix(course-users): insertUnique and only count and audit true inserts

src/Handler/Course/Users.hs

@@ -532,14 +532,17 @@ postCUsersR tid ssh csh = do
         Sum nrReg <- fmap mconcat . runDB . forM (Set.toList selectedUsers) $ \uid -> do
           now <- liftIO getCurrentTime
           -- TODO allow occurence
-          insert_ ExamRegistration
+          mExamReg <- insertUnique ExamRegistration
             { examRegistrationExam       = registerExam
             , examRegistrationUser       = uid
             , examRegistrationOccurrence = Nothing
             , examRegistrationTime       = now
             }
-          audit $ TransactionExamRegister registerExam uid
-          return 1
+          if isJust mExamReg
+            then do
+              audit $ TransactionExamRegister registerExam uid
+              return 1
+            else return 0
         addMessageI Success $ MsgCourseUsersExamRegistered nrReg
         redirect $ CourseR tid ssh csh CUsersR
   let headingLong  = [whamlet|_{MsgMenuCourseMembers} #{courseName course} #{tid}|]