Graphql | Apollo client | How to change variables in existing subscription?

Question

I have setup a Apollo Server and Client with Subscriptions. Everything works as expected in basic setup. I am using Apollo Client's Subscribe method for subscription. Something like below:

graphqlClient.subscribe({ query, variables }).subscribe({
next: d => {
  onData(d);
},
error: error => {
  handleErrorResponse(error).catch(e => {
    Logger.notifyError(new Error(`Real-time update error | ${e.message}.`));
  });
}

});

This works and I can see my onData callback firing on events.

Question - In our application, the Subscription filter is dynamic and user can select different values which will impact the filter. I have gone through documentation and many (many) articles but could not find a way to update filters or how to handle this use case?

Expectation - Once user selects any value and apply filter, I want to update my subscription on server to start using new filters?

Answer 1

Once created, you cannot modify the subscription. When the filter changes, you would need to call unsubscribe on the current Observer and then create a new Observer by calling the subscribe method with the updated variables. If you look at the source code, this is how react-apollo's Subscription component handles it. If you happen to be using React already, I would highly advise using the available component rather than trying to reinvent the wheel.