BP3_category_mutate.java

return newObject()
  .name("mutation")
  .field(newFieldDefinition()
         .name("category")
         .type(new GraphQLTypeReference("category"))
         .argument(newArgument()
                   .name("key")
                   .type(new GraphQLNonNull(GraphQLString))
                   .build())
         .argument(newArgument()
                   .name("name")
                   .type(new GraphQLNonNull(GraphQLString))
                   .build())
         .dataFetcher(env -> {
            Category category = new Category(env.getArgument("key"), 
                                             env.getArgument("name"));
            categoryDao.save(category);
            return category;
          })
         .build())