reimplement JobOccurrence as newtype; add JSON and PersistField instances

models/jobsystem.model

@@ -1,5 +1,5 @@
 -- Jobs to be fetched and distributed to the workers by the scheduler
 -- part of the *new* job system
 JobMeta
-  occurrence JobOccurrence default='{"dnf-terms":[]}'  -- when should the job be executed? (Possibly recurring)
+  occurrence JobOccurrence  -- when should the job be executed? (Possibly recurring)
   deriving Eq Ord Show Generic

src/Model/Types/Jobsystem.hs

@@ -1,9 +1,18 @@
 module Model.Types.Jobsystem
-  ( JobOccurrence
+  ( JobOccurrence(..)
   ) where
 
 import Import.NoModel
 
-type JobOccurrence = Occurrence LocalTime () -- latter is specialtime; not used yet
 
-derivePersistFieldJSON ''Occurrence LocalTime ()
+newtype JobOccurrence = JobOccurrence
+  { jobOccurrence :: Occurrence LocalTime () -- latter is specialtime; not used yet
+  }
+  deriving (Eq, Ord, Read, Show, Generic)
+  deriving anyclass (NFData)
+
+deriveJSON defaultOptions
+  { tagSingleConstructors = False
+  , unwrapUnaryRecords = True
+  } ''JobOccurrence
+derivePersistFieldJSON ''JobOccurrence