Target fields for input types

The @Source annotation extends output types by adding externally-defined fields. Its counterpart for input types is @Target (io.smallrye.graphql.api.Target).

With @Target, you can add fields to a GraphQL input type the same way @Source adds fields to an output type. The annotated parameter receives the input object, and a sibling parameter receives the value sent by the client for that field. The method name becomes the input field name in the schema (overridable with @Name), and @Description can be added on the method.

Server-side example:

import io.smallrye.graphql.api.Target;

@GraphQLApi
public class CharacterService {

    @Mutation
    public Character save(Character input) {
        // the input may have been modified by @Target methods below
        return input;
    }

    public void applyTwitterHandle(@Target Character character, String twitterHandle) {
        character.setTwitterHandle(twitterHandle);
    }
}

This generates an extended input type in the schema:

input CharacterInput {
    # ... regular fields ...
    twitterHandle: String   # added by the applyTwitterHandle method
}

When a client sends a mutation that includes the twitterHandle field, the corresponding @Target method is invoked at runtime. If the field is omitted, the method is not called.

Multiple @Target methods on the same input type are supported:

public void applyTwitterHandle(@Target Character character, String twitterHandle) {
    character.setTwitterHandle(twitterHandle);
}

public void applyNumber(@Target Character character, Integer rating) {
    character.setRating(rating);
}

A Context parameter can be injected into target methods:

public void applyWithContext(@Target Character character, String value, Context context) {
    String fieldName = context.getFieldName();
    // ...
}

[NOTE] @Target is currently marked as experimental.