In GraphQL, how can I specify nested arrays as a field type?

Question

In GraphQL, I'm trying to create a GeoJSON object type.

When I specify a 4-dimensional array of GraphQLFloats, I get an error when I start my server:

Error: Decorated type deeper than introspection query.

The type definition looks like this:

var GraphQLGeoJSON = new GraphQLObjectType({
  name: 'GeoJSON',
  fields: {
    type: {
      type: GraphQLString,
      resolve: (obj) => obj.type,
    },
    coordinates: {
      type: new GraphQLList(new GraphQLList(new GraphQLList(new GraphQLList(GraphQLFloat)))),
      resolve: (obj) => obj.coordinates,
    }
  }
});

How can I resolve this error? This is where it's thrown in the source:

https://github.com/graphql/graphql-js/blob/568dc52a4f9cc9bdec4f9283e6e528970af06cde/src/utilities/buildClientSchema.js#L105

Answer 1

We ended up defining a GeoJSON scalar type instead of an object type. This would allow us to perform strict validations against the GeoJSON spec. For now, just to keep us moving, we've defined a (completely unimplemented) custom GeoJSON type:

var GeoJSON = new GraphQLScalarType({
    name: 'GeoJSON',
    serialize: (value) => {
        // console.log('serialize value', value);
        return value;
    },
    parseValue: (value) => {
        // console.log('parseValue value', value);
        return value;
    },
    parseLiteral: (ast) => {
        // console.log('parseLiteral ast', ast);
        return ast.value;
    }
});

... which allows us to use it like this:

var Geometry = new GraphQLObjectType({
    name: 'Geometry',
    fields: () => ({
        id: globalIdField('Geometry'),
        geojson: {
            type: GeoJSON,
        },
    },
};

You could use this strategy to define a custom type to represent an array of arrays, or define a custom type to represent just the nested arrays, and then use new GraphQLList(CoordinatesType), etc. It depends on the data you're modeling.