Server does not start properly when a resolver is stored in database but not defined in schema

[darahayes]

Description

The server doesn't start when there is a resolver in the metadata db, but there is no matching Query/Mutation/Subscription in the schema. Example logs:

{"level":30,"time":1536137450457,"msg":"Using default schemaListener since SCHEMA_LISTENER_CONFIG environment variable is not defined","pid":19,"hostname":"data-sync-server-13-7gtkt","v":1}
--
  | {"level":50,"time":1536137451418,"msg":"Error while building schema.","pid":19,"hostname":"data-sync-server-13-7gtkt","v":1}
  | {"level":50,"time":1536137451418,"msg":"\"Subscription\" defined in resolvers, but not in schema","pid":19,"hostname":"data-sync-server-13-7gtkt","type":"Error","stack":"Error: \"Subscription\" defined in resolvers, but not in schema","v":1}
  | {"level":50,"time":1536137451419,"msg":"[object Promise]","pid":19,"hostname":"data-sync-server-13-7gtkt","type":"Error","stack":"Error: \"Subscription\" defined in resolvers, but not in schema","v":1}

Steps to reproduce

In the data-sync-ui, define a schema with some query/mutation/subscription. Add a matching resolver. Now comment out the query/mutation/subscription in the UI and restart the server. It does not initialize properly.

I would take a guess and say that an error would occur during schema reload also.

[psturc]

I just hit the same issue.
The origin of this issue is the same, but the scenario was a little bit different.

Steps: Delete the resolver which contains a subscription (it was selected from the dropdown), then remove it from the schema and restart server pod.

So apparently there's also a bug in the UI, because if you delete resolver containing subscription, UI should take care of removing resolver and subscription. But this doesn't happen.