fix: fix build & minor refactor

messages/uniworx/en-eu.msg

@@ -2378,5 +2378,3 @@ AllocationPrioritiesFile: CSV file
 AllocationPrioritiesSunk num: Successfully registered central priorities for #{num} #{pluralEN num "applicant" "applicants"}
 AllocationPrioritiesMissing num: Could not register central priorities for #{num} #{pluralEN num "applicant" "applicants"} because their matriculation was not found in the uploaded CSV file
 AllocationMissingPrioritiesIgnored: Applicants for whom no central priority has been registered will be ignored during assignment!
-ParticipantsIntersectCourseOption tid@TermId ssh@SchoolId coursen@CourseName: #{tid} - #{ssh} - #{coursen}
-ParticipantsIntersectCourses: Courses

src/Handler/Course/Users.hs

@@ -485,13 +485,11 @@ postCUsersR tid ssh csh = do
     mayRegister <- hasWriteAccessTo $ CourseR tid ssh csh CAddUserR
     ent@(Entity cid _) <- getBy404 $ TermSchoolCourseShort tid ssh csh
     hasTutorials <- exists [TutorialCourse ==. cid]
-    exams <- E.select . E.from $ \exam -> do
-      E.where_ $ exam E.^. ExamCourse E.==. E.val cid
-      return exam
     examOccurrencesPerExam <- E.select . E.from $ \(exam `E.LeftOuterJoin` examOccurrence) -> do
       E.on $ E.just (exam E.^. ExamId) E.==. examOccurrence E.?. ExamOccurrenceExam
       E.where_ $ exam E.^. ExamCourse E.==. E.val cid
       return (exam, examOccurrence)
+    let exams = nubOn entityKey $ examOccurrencesPerExam ^.. folded . _1
     let colChoices  = mconcat $ catMaybes
           [ pure $ dbSelect (applying _2) id (return . view (hasEntity . _entityKey))
           , pure $ colUserNameLink (CourseR tid ssh csh . CUserR)
@@ -582,11 +580,12 @@ postCUsersR tid ssh csh = do
             , examRegistrationOccurrence = mOccurrence
             , examRegistrationTime       = now
             }
-          if isJust mExamReg
-            then do
+          case mExamReg of
+            Just _ -> do
               audit $ TransactionExamRegister exam uid
               return 1
-            else return 0
+            Nothing ->
+              return mempty
         addMessageI Success $ MsgCourseUsersExamRegistered nrReg
         redirect $ CourseR tid ssh csh CUsersR
   let headingLong  = [whamlet|_{MsgMenuCourseMembers} #{courseName course} #{tid}|]