Support multiple unique fields in dgraph GraphQL

[jdgamble555 (Jonathan Gamble)]

@rajas I just wanted to give an example of a perfect use case for this. While you are building graphql facets, there is a need for this in basic graphs.

Let’s say a user reviews a movie, there should be only one review:

@jdgamble555

Basically, when we would create a rating, we would create the id as user_movie forcing a unique (composite) identifier based on the relationship.

Obviously, it would be better to have a unique restraint like in SQL:

ALTER TABLE `Rating` ADD UNIQUE `unique_index`(`user`, `movie`);

J