How do I support a query with aliases returning different data?

[nick-stephen]

Please can someone explain if/how DGS supports graphql aliases, especially for fields with different parameters.

Here is an example of the kind of query I'd like to be able to ask using the dgs-examples-java codebase:

Note that the example implementation specifies but ignores the minScore parameter today, but the returned list from average and best should be different.

I'd like to be able to retrieve different lists for average and best by passing in the arguments to the DataLoader, without the need for post-filtering in the DataFetcher.

Even better, I'm actually implementing using pre-loading, and it seems impossible to naively implement aliases like this using normal pre-loading populating each field including child fields, since there is only a single field to populate in DGS generated entities, so it'd appear essential to use the localContext plus multiple DataFetcher implementations, an update example doing this would be fabulous...

Many thx!

{
  shows {
    title
    average: reviews(minScore:3) {
      username
      starScore
    }
    best: reviews(minScore:5){
      username
      starScore
    }
  }
}

[nick-stephen]

I ended up implementing this in my codebase via the equivalent of

• pre-loading in the 'shows' query
  • creates a localContext which is an IdentityHashMap<Show, HashMap<String, Review>>
  • evaluates the values for all the fields of type 'reviews', including filtering, in the selectionSet() via a single query
  • creates a HashMap<String, Review> mapping the fieldName (alias name or normal field name) to each Review response
  • creates the 'Show' object without the 'reviews' field populated
  • returns a DataFetcherResult for the show query, with 'data' holding the show, and 'localContext' set to the IdentityHashMap

I then added a DataFetcher for the 'reviews' type which fetches the review from the localContext that is passed in through the DataFetchingEnvironment.

... my implementation dealt with a recursive LocalContext structure for the nested graph query, and had about a dozen parameterizable fields that were dealt with like this, so the actual IdentityHashMap type I used was , but the explanation remains the same. To avoid passing this around through the recursive methods that evaluate the query, I used a ThreadLocal.

Hope this might help someone.