feature: Directive that allows transformation of input types like we can on field resolvers

[SaranSundar]

Describe the Feature Request

I would like to be able to apply a @uppercase directive on a input string like so

directive @upperCase on INPUT_FIELD_DEFINITION

input JoinRoomInput {
    roomCode: String @upperCase
}

And then in a class that implements SchemaDirectiveWiring

we should be able to modify the input object so that when it reaches the mutation method, the roomCode string would be all transformed to uppercase.

@DgsMutation
public JoinRoom joinRoom(@InputArgument JoinRoomInput joinRoomInput) {

Describe Preferred Solution

Right now we can transform a field in an output type by doing something like this

  @Override
  public GraphQLFieldDefinition onField(SchemaDirectiveWiringEnvironment<GraphQLFieldDefinition> env )
  {
    GraphQLFieldDefinition field = env.getElement();
    GraphQLFieldsContainer parentType = env.getFieldsContainer();
    if (field.getDirective("stringCase") != null) {
      GraphQLArgument argument = field.getDirective("stringCase").getArgument("case");
      String argumentValue = ((EnumValue)argument.getArgumentValue().getValue()).getName();
 
      // build a data fetcher that transforms the given value to uppercase/lowercase
      DataFetcher originalFetcher = env.getCodeRegistry().getDataFetcher(parentType, field);
      DataFetcher dataFetcher = DataFetcherFactories.wrapDataFetcher(originalFetcher, ((dataFetchingEnvironment, value) -> {
        if (value instanceof String) {
          if (argumentValue.equalsIgnoreCase("UPPER")) {
            return ((String) value).toUpperCase();
          }
          if (argumentValue.equalsIgnoreCase("LOWER")) {
            return ((String) value).toLowerCase();
          }
        }
        return value;
      }));
 
      // now change the field definition to use the new uppercase/lowercase data fetcher
      env.getCodeRegistry().dataFetcher(parentType, field, dataFetcher);
    }
    return field;
  }

We should allow an input to be modified as well before it reaches the java mutation method.

[srinivasankavitha]

This should be possible to do with the existing mechanism. We will add documentation and some examples for it.

[berngp]

Related to DGS Examples Java.

[taptew]

Did anyone post an example of custom directive implementation on the input fields specifically. The issue is closed but I don’t see such example in the official docs. I am having hard time figuring it out. All the examples out there override data fetcher but that won’t be the case with input fields.

[figuldan]

Example of an input field implementation is still missing, any progress on this?