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import { UserInputError } from 'apollo-server';

const resolvers = {
  Query: {
    events(root, { zipCode }) {
      
      // do custom validation for user inputs
      const validationErrors = {};
      if (!isValidZipCode(zipCode)) {
        validationErrors.zipCode = 'This is not a valid zipcode';

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{
  "message": "Failed to get events due to validation errors",
  "extensions": {
    "code": "BAD_USER_INPUT",
    "exception": {
      "validationErrors": {
        "zipCode": "This is not a valid zipcode"
      }
    }
  }

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import ApolloClient from 'apollo-boost';

const client = new ApolloClient({
  uri: '<your graphql endpoint>',
  // Apollo Boost allows you to specify a custom error link for your client
  onError: ({ graphQLErrors, networkError, operation, forward }) => {
    if (graphQLErrors) {
      for (let err of graphQLErrors) {
        // handle errors differently based on its error code
        switch (err.extensions.code) {

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const typeDefs = gql`
  type Event {
    name: String!
    date: Date!
    capacity: Int!
    zipCode: String!
  }
`;

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const typeDefs = gql`
  # define wrapper result type that could return either
  # the added Event on success, or an array of Errors 
  # on error. Notice both fields are nullable. 
  type AddEventResult {
    event: Event
    validationErrors: [FieldValidationError!]
  }

  # define how you want errors to be represented. This

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{
  "data": {
    "searchMovies": {
      "movies": [
        {
          "name": "Avengers Infinity War",
        }
      ],
      "recommendedForYou": null,
    }

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const typeDefs = gql`
  type MovieSearchResult {
    movies: [Movie!]!
    recommendedForYou: [Movie!]
  }
  ...
`
// Note: since it makes no sense that we have a null
// Movie returned in the list, we should mark each Movie
// as non-nullable too. 

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import React from 'react';
import { Query } from 'react-apollo';

const MovieSearchResults = ({ keyword }) => (
  <Query query={SEARCH_MOVIES} variables={{ keyword }}>
    {(data, loading, error) => {
      if (loading) return <LoadingIndicator />;
      // if networkError is present, we can be sure that no data 
      // was returned. We can simply display an error component.
      if (error && error.networkError) return <ErrorDisplay />;

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const typeDefs = gql`
  type MovieSearchResult {
    movies: [Movie]
    recommendedForYou: [Movie]
  }

  type Query {
    searchMovies(keyword: String!): MovieSearchResult!
  }
`

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import { ApolloClient } from 'apollo-client';
import { InMemoryCache } from 'apollo-cache-inmemory';
import { HttpLink } from 'apollo-link-http';
const client = new ApolloClient({
  link: ApolloLink.from([
    // other links go here
    ReauthenticatonLink,
    new HttpLink({
      uri: 'http://graphql-endpoint:4000',
    }),