public CarModelQuery(CarModelRepository modelRepository) { Field <ListGraphType <CarModelType> >("models", resolve: context => { return(modelRepository.FindAllByPredicate(x => x.Versions)); }); Field <CarModelType>("model", arguments: new QueryArguments(new List <QueryArgument> { new QueryArgument <IdGraphType> { Name = "id" } }), resolve: context => { var id = context.GetArgument <int>("id"); if (id <= 0) { context.Errors.Add(new ExecutionError("Model Id is invalid or missing")); return(null); } return(modelRepository.FindBy(x => x.Id == id, x => x.Versions)); }); }