NIFI-4777 get schema by id even if not latest

[adfel70]

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[markap14]

@adfel70 thanks for the contribution! I'm a bit concerned about the ramifications of this change as-is, though. If I'm understanding the code change, it appears to be removing all caching from the controller service. I don't think that's what we want to do, as network problems or having the Confluent Schema Registry go down would cause the dataflow to stop. I think if we want to avoid the caching mechanism, then we would need to expose a property to allow the user to choose whether or not they want to do so - or how long they want to cache the schema.

[adfel70]

@markap14,
The schema registry still has a cache in here.
There were previously 2 caches, that was the reason i removed the ones in the rest client.
Instead the code runs and gets the schema at the particular id, instead of the latest, since it created a bug in our nifi workflow.

[adfel70]

Hey could anyone else help me with this?
if it is compulsory i can return the second cache

[markap14]

Hey @adfel70 I think I was looking at this PR the wrong way. I didn't notice the addition of the POST request, which is very vital. Because of that, I thought this was making a very large number of requests, but after reviewing the confluent API docs and reviewing the code again it all makes sense. The caching in this layer is different than the caching at the higher layer but was only really necessary for the routine that was there previously, before the POST request. I think your solution handles this case much better than the previous solution. And more importantly your solution appears to be correct :) I was able to test locally and see that if i changed the schema reference to an older version of an existing schema that things work correctly with this PR and did not without the PR. So I've merged this to master. Thanks for the fix and for the patience in getting it all sorted out!