Relationships GraphQL - mongodb

Question

The second week I try to link two collections in the apollo-server-express / MongoDB / Mongoose / GraphQL stack, but I do not understand how. I found a similar lesson with the REST API, what I need is called Relationships. I need this, but in GraphQL
watch video
How to add cars to the User?
I collected the test server, the code is here: https://github.com/gHashTag/test-graphql-server
Help

Answer 1

I have cloned your project and implemented some code and here what I changed to make relationship works. Note, I just did a basic code without validation or advance dataloader just to make sure non-complexity. Hope it can help.
src/graphql/resolvers/car-resolvers.js
import Car from '../../models/Car'
import User from '../../models/User'
export default {
getCar: (_, { _id }) => Car.findById(_id),
getCars: () => Car.find({}),
getCarsByUser: (user, {}) => Car.find({seller: user._id }), // for relationship
createCar: async (_, args) => {
// Create new car
return await Car.create(args)
}
}
src/graphql/resolvers/user-resolvers.js
import User from '../../models/User'
export default {
getUser: (_, { _id }) => User.findById(_id),
getUsers: () => User.find({}),
getUserByCar: (car, args) => User.findById(car.seller), // for relationship
createUser: (_, args) => {
return User.create(args)
}
}
src/graphql/resolvers/index.js
import UserResolvers from './user-resolvers'
import CarResolvers from './car-resolvers'
export default {
User:{
cars: CarResolvers.getCarsByUser // tricky part to link query relation ship between User and Car
},
Car:{
seller: UserResolvers.getUserByCar // tricky part to link query relation ship between User and Car
},
Query: {
getUser: UserResolvers.getUser,
getUsers: UserResolvers.getUsers,
getCar: CarResolvers.getCar,
getCars: CarResolvers.getCars
},
Mutation: {
createUser: UserResolvers.createUser,
createCar: CarResolvers.createCar,
}
}
src/graphql/schema.js
export default`
type Status {
message: String!
}
type User {
_id: ID!
firstName: String
lastName: String
email: String
cars: [Car]
}
type Car {
_id: ID
make: String
model: String
year: String
seller: User
}
type Query {
getUser(_id: ID!): User
getUsers: [User]
getCar(_id: ID!): Car
getCars: [Car]
}
type Mutation {
createUser(firstName: String, lastName: String, email: String): User
// change from _id to seller, due to base on logic _id conflict with CarId
createCar(seller: ID!, make: String, model: String, year: String): Car
}
schema {
query: Query
mutation: Mutation
}
`
src/middlewares.js
import bodyParser from 'body-parser'
import { graphqlExpress, graphiqlExpress } from 'apollo-server-express'
import { makeExecutableSchema } from 'graphql-tools'
import typeDefs from '../graphql/schema'
import resolvers from '../graphql/resolvers'
import constants from './constants'
export const schema = makeExecutableSchema({
typeDefs,
resolvers
})
export default app => {
app.use('/graphiql', graphiqlExpress({
endpointURL: constants.GRAPHQL_PATH
}))
app.use(
constants.GRAPHQL_PATH,
bodyParser.json(),
graphqlExpress(req => ({
schema,
context: {
event: req.event
}
}))
)
}

Answer 2

try to make something like this in your car resolver
export default {
getCar: ({ _id: ownId }, { _id }) =>
Car.findById(ownId || _id);
// here is the rest of your code

Answer 3

You need to add a resolver for the cars field on the User type.
const resolvers = {
Query: {
getUsers: ...
getCars: ...
...
},
Mutation: {
...
},
User: {
cars: ...
}
}