Add example of server-side validation failure

[cesarandreu]

Not sure if this belongs here or graphql-relay-js.

If you have validation that can only be done on the server, it's not clear how you can notify the client and how to handle it.

I asked about this in Reactiflux and someone pointed out I can throw in mutateAndGetPayload, and handle it in the onFailure callback of update.

Having a small server-side failure example would be really helpful.

[u9520107]

If you throw in mutateAndGetPayload, the errors will be sent to the browser.
But currently in the onFailure callback, transaction.getError() will return the errors in a string.
If you have multiple errors, their error messages will be listed out.

Come to think about it, this is rather inconvenient if we want to address those errors differently.
Or if I simply want to send an error code and display some error message in the language of the browser.
I think having a way to access the error objects separately is better. This may even allow us to provide more data to the client-side if necessary.

[mmurray]

@u9520107 transaction.getError() actually returns an error object. And it seems you can get an array of the individual errors from transaction.getError().source.errors.

[steveluscher]

This is great discussion. Can we get this on Stack Overflow as a question, where it will endure long after this issue is closed?

https://stackoverflow.com/questions/ask?tags=relayjs

If you think there's something better Relay could be doing here, feel free to open a separate issue with a suggestion.

[rterysen-openroad]

@cesarandreu Would love a snippet or a more detailed example of handing server side validation. I see tons of examples of relay but none are geared towards real world scenarios.

http://stackoverflow.com/questions/38706347/relay-mutation-with-serverside-validation