schema.js

const {
    GraphQLobjectType,
    GraphQLString,
    GraphQLInt,
    GraphQLSchema,
    GraphQLList,
    GraphQLNonNull
} = require('graphql');

// Customer Type
const CustomerType = new GraphQLObjectType({
    name: 'Customer',
    fields: () => ({
        id: {
            type: GraphQLString
        },
        name: {
            type: GraphQLString
        },
        email: {
            type: GraphQLString
        },
        age: {
            type: GraphQLInt
        },
    })
});

// Root Query
const RootQuery = new GraphQLObjectType({
    name: 'RootQueryType',
    fields: {
        customer: {
            type: CustomerType,
            args: {
                id: {
                    type: GraphQLString
                }
            },
            resolve(parentValue, args) {
                /*
                for(let i = 0;i < customers.length;i++){
                    if(customers[i].id == args.id){
                        return customers[i];
                    }
                }
                */
                return axios.get('http://localhost:3000/customers/' + args.id)
                    .then(res => res.data);

            }
        },
        customers: {
            type: new GraphQLList(CustomerType),
            resolve(parentValue, args) {
                return axios.get('http://localhost:3000/customers')
                    .then(res => res.data);
            }
        }
    }
});

// Mutations
const mutation = new GraphQLObjectType({
    name: 'Mutation',
    fields: {
        addCustomer: {
            type: CustomerType,
            args: {
                name: {
                    type: new GraphQLNonNull(GraphQLString)
                },
                email: {
                    type: new GraphQLNonNull(GraphQLString)
                },
                age: {
                    type: new GraphQLNonNull(GraphQLInt)
                }
            },
            resolve(parentValue, args) {
                return axios.post('http://localhost:3000/customers', {
                        name: args.name,
                        email: args.email,
                        age: args.age
                    })
                    .then(res => res.data);
            }
        },
        deleteCustomer: {
            type: CustomerType,
            args: {
                id: {
                    type: new GraphQLNonNull(GraphQLString)
                }
            },
            resolve(parentValue, args) {
                return axios.delete('http://localhost:3000/customers/' + args.id)
                    .then(res => res.data);
            }
        },
        editCustomer: {
            type: CustomerType,
            args: {
                id: {
                    type: new GraphQLNonNull(GraphQLString)
                },
                name: {
                    type: GraphQLString
                },
                email: {
                    type: GraphQLString
                },
                age: {
                    type: GraphQLInt
                }
            },
            resolve(parentValue, args) {
                return axios.patch('http://localhost:3000/customers/' + args.id, args)
                    .then(res => res.data);
            }
        },
    }
});

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