Fix source transfer

[nivemaham]

• Adds validation for source update and source transfer occasions.
• A source cannot be transfered to another project if it is assigned
• A source cannot be transfered to a project which doesn't have compatible source-type.

Fixes #239

[dennyverbeeck]

Just one request, otherwise looks great!

[dennyverbeeck]

I think we should move all this logic into SourceService, including the call to save(). This would make the code more re-usable, plus it would make the whole update transactional.

[nivemaham]

Indeed. That was my preferred method. But the problem is mainly due to the inconsistent way of error handling. We have two ways of error handling. One is by throwing exception and have the ExceptionTranslator to translate this into body. However, it deviates from the original method that was followed in the FrontEnd app. It expects headers with custom parameters to show proper messages to the user. So I decided to stick to responding with headers, because this action mainly involves user interaction and proper message on the front end seems essential. I didn't want to return ResponseEntity from SourceService either. It sounded far from SourceService logics. So I chose this way.

[dennyverbeeck]

Hmm, i thought the frontend could handle also error messages in the body, but i might be mistaken. If not we can modify the ExceptionTranslator to set the headers, and use exceptions everywhere.

Ok let's keep it here for now and revisit the error handling later, but i would feel safer with at least the save() being delegated to the service so it's transactional 😄

[nivemaham]

Yes. That is what I thought. So I will push the exceptionHandler changes too. I was thinking of doing it separately. But same PR doesn't hurt.
Save is done through SourceService which is Transactional.
SourceDTO result = sourceService.save(sourceDto);

[nivemaham]

I don't know why we have specific annotations for some methods in classes which are Transactional.

[dennyverbeeck]

Save is done through SourceService which is Transactional. SourceDTO result = sourceService.save(sourceDto);

Sorry, of course, my bad!

I don't know why we have specific annotations for some methods in classes which are Transactional.

Indeed, the method-level annotations can go away if there is a class-level one.