Dataloader not working with GraphQL subscriptions

When trying to query dataloaded relationships via a GraphQl subscription, you get the following:

"message": "Cannot read property 'typeormGetConnection' of undefined",

I believe it is because the ApolloServerLoaderPlugin is not being passed to the WS server:

        async serverWillStart() {
          return {
            async drainServer() {
              subscriptionServer.close();
            },
          };
        },
      },
      ApolloServerLoaderPlugin({
        typeormGetConnection: getConnection,
      }),

anyone have an ideas on this?

[nelsonfleig]

Similar issue here. The data loader doesn't get passed to a subscription.

When querying subfields from a client I get an error Unhandled GraphQL subscription error Error: Cannot read properties of undefined (reading '_tgdContext').

My query:

subscription PostAdded {
  post: postAdded {
    id
    title
    likes
    user {
      username
    }
  }
}

On regular queries and mutations, selecting a subfield like user works perfectly.

Any ideas on how to fix this?

[nelsonfleig]

So I figured that because the subscription server is no longer built-in in Apollo V3, it would be worth a try to manually add the missing _tgdContext to the subscription context. I took a look in ApolloServerLoaderPlugin.ts and just copied the code. Here is how to add _tgdContext to the subscription server context, in order to load all relations.

const serverCleanup = useServer(
  {
    schema, // Your executable schema
    context: (ctx: any) => {
        Object.assign(ctx, {
          _tgdContext: {
            requestId: uuidv4(),
            typeormGetConnection: TypeORM.getConnection, // same getConnection method passed to the ApolloServerLoaderPlugin
          },
        });
       return ctx;
    },
  },
  wsServer // your wsServer created with WebSocketServer
);

Then do the same as the OP, and copy the following to the ApolloServer plugins array:

{
  async serverWillStart() {
    return {
      async drainServer() {
        await serverCleanup.dispose();
      },
    };
  },
},

Hope this helps anyone.