Hi guys,

I have spent some time looking for a solution on how to implement data validation in graphql using directives. The idea seems very nice and clear: schema directives define validation rules to be applied to the data, eg

input ConsumerData {
  name: String @length(min: 1, max: 20)
}

However current approach described in the documentation refers to output types of directives only and suggests usage of Consumer<GraphQLFieldDefinition.Builder> together with GraphQLFieldDefinition.dataFetcher.

Applying the same approach to GraphQLInputObjectField wouldn't work since GraphQLInputObjectField doesn't have any kind of data transformer.

Would it make sense to add something like

interface DataTransformer<T> {
    public T transform(T value)
}

to GraphQLInputObjectField for the purpose of usage of directives? This could be used in ValuesResolver.coerceValueAstForInputObject.

To supply a DataTransformer to ValuesResolver one could use the same wiring approach as one currently used to update dataFetcher on GraphQLFieldDefinition.