getted data is only null in apollo-client / apollo-server & useSubscription - apollo

Question

I try use pubsub in apollo server & apollo client. but subscribed data is only null.
client dependency
"#apollo/react-hooks": "^3.1.5",
"apollo-boost": "^0.4.9",
"apollo-link-ws": "^1.0.20",
"graphql": "^15.0.0",
"react": "^16.13.1",
"react-dom": "^16.13.1",
"react-router-dom": "^5.2.0",
"react-scripts": "3.4.1",
"styled-components": "^5.1.1",
"subscriptions-transport-ws": "^0.9.16",
"typescript": "~3.7.2"
server dependency
"apollo-server": "^2.14.1",
"graphql": "^15.0.0",
"merge-graphql-schemas": "^1.7.8",
"ts-node": "^8.10.2",
"tsconfig-paths": "^3.9.0",
"typescript": "^3.9.3"
// apolloClient.ts
import { ApolloClient, HttpLink, InMemoryCache, split } from 'apollo-boost'
import { WebSocketLink } from 'apollo-link-ws'
import { getMainDefinition } from 'apollo-utilities'
const wsLink = new WebSocketLink({
uri: 'ws://localhost:4000/graphql',
options: {
reconnect: true
}
})
const httpLink = new HttpLink({
uri: 'http://localhost:4000'
})
const link = split(
// split based on operation type
({ query }) => {
const definition = getMainDefinition(query);
return (
definition.kind === 'OperationDefinition' &&
definition.operation === 'subscription'
);
},
wsLink,
httpLink,
)
const cache = new InMemoryCache()
const client = new ApolloClient({
cache: cache,
link: link,
})
export default client
// subscribe.ts
const ON_PUT_UNIT = gql`
subscription onPutUnit($code: String!) {
onPutUnit(code: $code)
}
`
const onPutResult = useSubscription(
ON_PUT_UNIT,
{ variables: {
code: code,
}}
)
// in is only null!!
console.log('subscribe', onPutResult)
-server-
onPutUnit.ts
type Subscription {
onPutUnit(code: String!): Room
}
import { pubsub } from '#src/index'
const { withFilter } = require('apollo-server')
export default {
Subscription: {
onPutUnit: {
subscribe: withFilter(
() => pubsub.asyncIterator(['PUT_UNIT']),
(payload: any, variables: any) => {
// no problem in payload & variable data
return payload.code === variables.code
}
)
}
},
}
putUnit.ts
type Mutation {
putUnit(code: String!, x: Int!, y: Int!, userName: String!): Room!
}
export default {
Mutation: {
putUnit: async (_: any, args: args) => {
const { code, x, y, userName } = args
const room = findRoom(code)
console.log(room) // no problem. normal data.
pubsub.publish('PUT_UNIT', room)
return room
},
},
}
Is it some problem? subscribe event is normally reached to client when publish. but data is is only null. I can't fine the reason.

Answer 1

You only specified a subscribe function for onPutUnit, without specifying a resolve function. That means the field utilizes the default resolver.
The default resolver just looks for a property with the same name as the field on the parent object (the first parameter passed to the resolver) and returns that. If there is no property on the parent object with the same name as the field, then the field resolves to null. The parent object is the value the parent field resolved to. For example, if we have a query like this:
{
user {
name
}
}
whatever the resolver for user returns will be the parent value provided to the resolver for name (if user returns a Promise, it's whatever the Promise resolved to).
But what about user? It has no parent field because it's a root field. In this case, user is passed the rootValue you set when initializing the ApolloServer (or {} if you didn't).
With subscriptions, this works a bit differently because whatever value you publish is actually passed to the resolver as the root value. That means you can take advantage of the default resolver by publishing an object with a property that matches the field name:
pubsub.publish('PUT_UNIT', { onPutUnit: ... })
if you don't do that, though, you'll need to provide a resolve function that transforms the payload you published. For example, if we do:
pubsub.publish('PUT_UNIT', 'FOOBAR')
Then our resolver map needs to look something like this:
const resolvers = {
Subscription: {
onPutUnit: {
subscribe: ...,
resolve: (root) => {
console.log(root) // 'FOOBAR'
// return whatever you want onPutUnit to resolve to
}
}
},
}