Why doesn't GraphQL accept this scalar argument type, instead complaining "argument type must be Input Type but got: undefined"?

Question

I have

export const getPicture = {
    type: GraphPicture,
    args: {
        type: new GraphQLNonNull(GraphQLInt)
    },
    resolve(_, args) {
        return Picture.findByPrimary(args.id);
    }
};

export const getPictureList = {
    type: new GraphQLList(GraphPicture),
    resolve(_, __, session) {
        return Picture.findAll({where: {owner: session.userId}});
    }
};

and

const query = new GraphQLObjectType({
    name: 'Queries',
    fields: () => {
        return {
            getPictureList: getPictureList,
            getPicture: getPicture
        }
    }
});

const schema = new GraphQLSchema({
    query: query,
    mutation: mutation
});

Which throws:

Error: Queries.getPicture(type:) argument type must be Input Type but got: undefined.

getPictureList works fine; getPicture fails with a scalar argument type of GraphQLInt or GraphQLNonNull(GraphQLInt). I have tried making getPicture a GraphQLLIst, but it didn't help. I have tried making the argument type an Input Type, but it didn't help.

Why is the code generating the error, and how can it be fixed?

The stack trace is:

Error: Queries.getPicture(type:) argument type must be Input Type but got: undefined.
    at invariant (/home/jrootham/dev/trytheseon/node_modules/graphql/jsutils/invariant.js:19:11)
    at /home/jrootham/dev/trytheseon/node_modules/graphql/type/definition.js:307:33
    at Array.map (native)
    at /home/jrootham/dev/trytheseon/node_modules/graphql/type/definition.js:304:52
    at Array.forEach (native)
    at defineFieldMap (/home/jrootham/dev/trytheseon/node_modules/graphql/type/definition.js:293:14)
    at GraphQLObjectType.getFields (/home/jrootham/dev/trytheseon/node_modules/graphql/type/definition.js:250:46)
    at /home/jrootham/dev/trytheseon/node_modules/graphql/type/schema.js:224:27
    at typeMapReducer (/home/jrootham/dev/trytheseon/node_modules/graphql/type/schema.js:236:7)
    at Array.reduce (native)
    at new GraphQLSchema (/home/jrootham/dev/trytheseon/node_modules/graphql/type/schema.js:104:34)
    at Object. (/home/jrootham/dev/trytheseon/server/graphQL.js:45:16)
    at Module._compile (module.js:399:26)
    at normalLoader (/usr/lib/node_modules/babel/node_modules/babel-core/lib/babel/api/register/node.js:160:5)
    at Object.require.extensions.(anonymous function) [as .js] (/usr/lib/node_modules/babel/node_modules/babel-core/lib/babel/api/register/node.js:173:7)
    at Module.load (module.js:345:32)
    at Function.Module._load (module.js:302:12)
    at Module.require (module.js:355:17)
    at require (internal/module.js:13:17)
    at Object. (/home/jrootham/dev/trytheseon/devServer.js:14:44)
    at Module._compile (module.js:399:26)
    at normalLoader (/usr/lib/node_modules/babel/node_modules/babel-core/lib/babel/api/register/node.js:160:5)

Answer 1

The problem isn't the return type of the query but the type you have specified to your args.

export const getPicture = {
    type: GraphPicture,
    args: {
        type: new GraphQLNonNull(GraphQLInt)
    },
    resolve(_, args) {
        return Picture.findByPrimary(args.id);
    }
};

Assuming you meant to have an argument named "type" it should be:

export const getPicture = {
    type: GraphPicture,
    args: {
        type: {
             type: new GraphQLNonNull(GraphQLInt)
        }
    },
    resolve(_, args) {
        return Picture.findByPrimary(args.id);
    }
};

here is an example from the graphql-js repo:

hero: {
  type: characterInterface,
  args: {
    episode: {
      description: 'If omitted, returns the hero of the whole saga. If ' +
                   'provided, returns the hero of that particular episode.',
      type: episodeEnum
    }
  },
  resolve: (root, { episode }) => getHero(episode),
},

See the full schema from the graphql-js repo here: https://github.com/graphql/graphql-js/blob/master/src/tests/starWarsSchema.js

Answer 2

Just for reference, I got here searching the same error just not with undefined, but with my own Product type:

... argument * must be Input Type but got Product

Turned out that in GraphQL what you pass to a Mutation should be either scalar type (String, Integer, ...) or user defined input type, not type type.

http://graphql.org/graphql-js/mutations-and-input-types/

input ProductInput {
  id: ID
  name: String
}

I was trying to pass in my Product type:

type Product {
  id: ID
  name: String
}

This feels a bit redundant, but guess, I'll be glad for having it separated later.