How to update variables in subscribe?

[alucardu]

I have a service, in this service I initiate a subscription:

session.service.ts

constructor(
  private apollo: Apollo,
  private notificationService: NotificationService
) {
  this.subscribeToSessions();
}

//

private subscribeToSessions(): void {
  this.apollo.subscribe<UserJoinedSession>({
    query: USER_JOINED_SESSION,
    variables: {
      id: this.sessionSubject.getValue()?.id
    },
  }).subscribe({
    next: ({data}) => {
      console.log(data)
    }
  })
}

I call this subscription when a user is connected to a session:

session.resolvers.js

connectUserToSession: async (_, args) => {
  const session = await prisma.session.update({
    where: {
      id: Number(args.sessionId)
    },
    data: {
      players: {
        connect: {
          id: Number(args.userId)
        }
      }
    },
    include: {
      players: true,
      host: true
    }
  })

  pubsub.publish('USER_JOINED_SESSION', { userJoinedSession: session })

  return session
},
// working on this
userJoinedSession: {
  subscribe: withFilter(() => pubsub.asyncIterator('USER_JOINED_SESSION'),
    (payload, variables) => {
      console.log(variables)
      return true
    },
  ),
},

My goal is to send notifications only to users who are also connected to that session. To achieve this I want to to send the session object that a user is connected to from the client to the server and then use that in the withFilter().

The problem I'm encountering is that in the client when the service is initiated it initiates the subscriptions with the value of this.sessionSubject.getValue()?.id which is null (since a user hasn't joined a session yet).

But this value never gets updated. How can I achieve that?