__typename is null when an optimistic update is applied

[calebmer]

I have a Node that I want to update with an optimistic update, but that Node is also returned by a union so I need to get the __typename from the union. However, it would appear that after an optimistic update has been applied and before the response comes back, the value of that __typename on the union is null.

[josephsavona]

Just to clarify, are you explicitly setting the __typename field in your optimistic response?

[calebmer]

No

[calebmer]

It does work when __typename is set in getOptimisticResponse though. Is this expected behavior?

[josephsavona]

Yes, this is expected behavior. Relay can't know what type you meant to create within a union, so you have to specify it. It may be possible to infer the type in some cases that we don't today, but a union would always require it to be specified by the user.

[wincent]

Going to close this out, but feel free to comment again @calebmer if you'd like to know more. Thanks for bringing this up.