Apollo GraphQL - TypeError: Cannot read property 'findOrCreateUser' of undefined

Question

I'm following this tutorial https://www.apollographql.com/docs/tutorial/mutation-resolvers/#book-trips

and have ended up getting this error:

"TypeError: Cannot read property 'findOrCreateUser' of undefined",
            "    at login 

Below is the function I use to call login:

mutation LoginUser {
  login(email: "[email protected]") {
    token
  }
}

The file below is where findOrCreateUser is called: src/resolvers.js

module.exports = {
    Mutation: {
        login: async (_, {email}, {dataSources}) => {
            const user = await dataSources.userAPI.findOrCreateUser({ email });
            if (user) {
                user.token = Buffer.from(email).toString('base64');
                return user;
            }
        },
    },

This is where dataSources is defined: src/index.js

require('dotenv').config();
const { ApolloServer } = require('apollo-server');
const typeDefs = require('./schema');
const { createStore } = require('./utils');
const resolvers = require('./resolvers');
const isEmail = require('isemail');

const LaunchAPI = require('./datasources/launch');
const UserAPI = require('./datasources/user');

const store = createStore();

const server = new ApolloServer({
    context: async ({req}) => {
        const auth = req.headers && req.headers.authorization || '';
        const email = Buffer.from(auth, 'base64').toString('ascii');
        if (!isEmail.validate(email)) return {user: null};
        // find a user by their email
        const users = await store.user.findOrCreate({ where: { email } });
        const user = users && users[0] || null;
        return { user: {...user.dataValues } };
    },
    dataSources: () => ({
        launchAPI: new LaunchAPI(),
        UserAPI: new UserAPI({store})
    }),
    typeDefs,
    resolvers,
});

server.listen().then(() => {
    console.log(`
        Server is running!
        Listening on port 4000
        Explore at https://studio.apollographql.com/dev
    `)
});

Answer 1

As xadm mentioned in the comment the issues is your usage of userAPI vs UserAPI. the datasource object is created in index.js in the following block

dataSources: () => ({
        launchAPI: new LaunchAPI(),
        UserAPI: new UserAPI({store})
    }),

here you defined datasources.UserAPI however in resolvers.js you refer to it as datasources.userAPI (note the difference in capitalization of userAPI). Your problem can be resolved by changing the above code block to

dataSources: () => ({
        launchAPI: new LaunchAPI(),
        userAPI: new UserAPI({store})
    }),