schema.js

const graphql = require('graphql');

const Todo = require('../models/todo');

const {
    GraphQLObjectType,
    GraphQLString,
    GraphQLBoolean,
    GraphQLSchema,
    GraphQLID,
    GraphQLList,
    GraphQLNonNull
} = graphql;

const TodoType = new GraphQLObjectType({
    name: 'todos',
    fields: () => ({
        id: {
            type: GraphQLID
        },
        title: {
            type: GraphQLString
        },
        completed: {
            type: GraphQLBoolean
        },
    })
});

const RootQuery = new GraphQLObjectType({
    name: 'RootQueryType',
    fields: {
        todo: {
            type: TodoType,
            args: {
                id: {
                    type: GraphQLID
                }
            },
            resolve(parent, args) {
                return Todo.findById(args.id);
            }
        },
        Todos: {
            type: new GraphQLList(TodoType),
            resolve(parent, args) {
                return Todo.find({});
            }
        }
    }
});

const Mutation = new GraphQLObjectType({
    name: 'Mutation',
    fields: {
        addTodo: {
            type: TodoType,
            args: {
                title: {
                    type: new GraphQLNonNull(GraphQLString)
                },
                completed: {
                    type: new GraphQLNonNull(GraphQLBoolean)
                },
            },
            resolve(parent, args) {
                let todo = new Todo({
                    title: args.title,
                    completed: args.completed,
                });
                return todo.save();
            }
        }
    }
})

module.exports = new GraphQLSchema({
    query: RootQuery,
    mutation: Mutation
});