fix(csv upload exams): allow ambiguous harmless study fields

src/Handler/Exam/Users.hs

@@ -617,7 +617,11 @@ postEUsersR tid ssh csh examn = do
               lookupStudyFeatures :: ExamUserTableCsv -> DB (Maybe StudyFeaturesId)
               lookupStudyFeatures csv@ExamUserTableCsv{..} = do
                 uid <- view _2 <$> guessUser csv
-                studyFeatures <- E.select . E.from $ \(studyFeatures `E.InnerJoin` studyDegree `E.InnerJoin` studyTerms) -> do
+                oldFeatures <- getBy $ UniqueParticipant uid examCourse
+                studyFeatures <- E.select . E.from $ \(studyFeatures `E.InnerJoin` studyDegree `E.InnerJoin` studyTerms) ->
+                  E.distinctOnOrderBy [ E.asc (studyFeatures E.^. StudyFeaturesField)
+                                      , E.asc (studyFeatures E.^. StudyFeaturesDegree)
+                                      , E.asc (studyFeatures E.^. StudyFeaturesSemester)] $ do
                     E.on $ studyTerms E.^. StudyTermsId E.==. studyFeatures E.^. StudyFeaturesField
                     E.on $ studyDegree E.^. StudyDegreeId E.==. studyFeatures E.^. StudyFeaturesDegree
                     E.where_ . E.and $ catMaybes
@@ -644,6 +648,7 @@ postEUsersR tid ssh csh examn = do
                           E.where_ $ courseParticipant E.^. CourseParticipantField  E.==. E.just (studyFeatures E.^. StudyFeaturesId)
                     E.where_ $ (studyFeatures E.^. StudyFeaturesValid E.==. E.val True)
                       E.||. isCourseParticipantFeature -- either active studyFeature or the one previously associated with the course
+                    E.orderBy [E.desc isCourseParticipantFeature, E.asc (E.orderByOrd $ studyFeatures E.^. StudyFeaturesType)]
                     E.limit 2 -- we just need to know whether there is a unique one, none, or more than one
                     return $ studyFeatures E.^. StudyFeaturesId
                 case studyFeatures of
@@ -653,6 +658,11 @@ postEUsersR tid ssh csh examn = do
                     , is _Nothing csvEUserDegree
                     , is _Nothing csvEUserSemester
                     -> return Nothing
+                  _other
+                    | Just (Entity _ CourseParticipant{..}) <- oldFeatures
+                    , Just sfid <- courseParticipantField
+                    , E.Value sfid `elem` studyFeatures
+                    -> return Nothing
                   _other        -> throwM ExamUserCsvExceptionNoMatchingStudyFeatures
 
       examUsersDBTableValidator = def & defaultSorting [SortAscBy "user-name"]

src/Model/Types/Misc.hs

@@ -19,6 +19,8 @@ import qualified Data.Text.Lens as Text
 data StudyFieldType = FieldPrimary | FieldSecondary
   deriving (Eq, Ord, Enum, Show, Read, Bounded, Generic)
 derivePersistField "StudyFieldType"
+instance Universe StudyFieldType
+instance Finite   StudyFieldType
 
 
 data Theme