Job Results

A handler can produce a result. With transactionalWorkerConfig, return the result. With a manual or batched configuration, pass it to ackWith or ackAllWith.

Arbiter stores a result only in these conditions:

• Job with a parent: Arbiter stores the result for the parent to read with Worker.childResults or Worker.mergedChildResults. It removes the result after the parent completes.
• Standalone root job: Arbiter stores the result in the job archive entry if archiving is enabled for that job. If archiving is disabled, Arbiter discards the result.

Arbiter uses ToJSON to store a result and FromJSON to read it. Records and sum types with these instances can be result types.

A parent can use Worker.childResults or Worker.mergedChildResults. Worker.mergedChildResults requires a Monoid result type and combines the child results. It replaces a result that it cannot decode with mempty. A change to the result format can therefore cause an incomplete rollup. Worker.childResults returns an Either for each child and lets the caller handle decode errors.

Use a Maybe result type to make storage conditional for each run. Nothing does not create an archive result or a result row for a parent.

data SyncReport = SyncReport
  { rowsChanged :: Int
  , notes :: [Text]
  }
  deriving stock (Eq, Show, Generic)
  deriving anyclass (ToJSON, FromJSON)

type SyncRegistry = '[ QueueWithResult "sync_queue" SyncPayload (Maybe SyncReport) ]

syncHandler :: Arb.JobHandler (ArbS.SimpleDb SyncRegistry IO) SyncPayload (Maybe SyncReport)
syncHandler _conn job = do
  report <- runSync (Arb.payload job)
  pure $ if rowsChanged report == 0 then Nothing else Just report

See the Arbiter.Core.JobResult haddocks for how a result is encoded.