CODEWITHSUNDEEP
typescriptgraphqlnestjsapollo-server
Yue Dong
Yue Dong

Reputation: 85

Nestje subscription getting NULL and with the error: "Cannot return null for non-nullable field Subscription"

This is a simple test for Subscription in my nestjs project with graphql, but I got the error: Cannot return null for non-nullable field Subscription

Here is the code:

  //* ~~~~~~~~~~~~~~~~~~~ Subscription ~~~~~~~~~~~~~~~~~~~ */
  @Mutation((returns) => Boolean)
  testSubscription() {
    pubsub.publish('somethingOnTrack', {
      somethingOnTrack: 'something',
    });
    return true;
  }
  @Subscription((returns) => String)
  orderSubscription() {
    return pubsub.asyncIterator('somethingOnTrack');
  }
Just create a subscription and test it.

Here is the GraphQLModule in the app.module in nestjs:

GraphQLModule.forRoot<ApolloDriverConfig>({
  driver: ApolloDriver,
  autoSchemaFile: true,
  subscriptions: {
    'graphql-ws': true,
    'subscriptions-transport-ws': true,
  },
}),

it try to using graphql-ws & subscriptions-transport-ws

Next, I test it in the graphql:

subscription {
  orderSubscription
}

mutation {
  testSubscription
}

The Mutation can get result as expected:

{
  "data": {
    "testSubscription": true
  }
}

But the Subscription got the error:

{
  "errors": [
    {
      "message": "Cannot return null for non-nullable field Subscription.orderSubscription.",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "orderSubscription"
      ]
    }
  ],
  "data": null
}

Seems the subscription cannot get the payload from the pubsub.publish? Why I got this error?

Upvotes: 0

Views: 1633

Answers (1)

Yue Dong
Yue Dong

Reputation: 85

Cz this is code first, just return the type String in Subscription seems not make any sense, Finally, add a output type dto:

import { Field, ObjectType } from '@nestjs/graphql';

@ObjectType()
export class SubscriptionOutput {
  @Field((type) => String)
  somethingOnTrack: string;
}

And also add {resolve: ...} to the Subscription, seems it is the correct syntax?? Change the test Subscription to follow:

  //* ~~~~~~~~~~~~~~~~~~~ Subscription ~~~~~~~~~~~~~~~~~~~ */
  @Mutation((returns) => Boolean)
  testSubscription() {
    this.pubsub.publish('somethingOnTrack', { somethingOnTrack: 'something' });
    return true;
  }
  @Subscription((returns) => SubscriptionOutput, {
    resolve: (payload) => payload,
  })
  orderSubscription() {
    return this.pubsub.asyncIterator('somethingOnTrack');
  }

Upvotes: 1

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