Subscriptions seem to have a caching issue

[philiiiiiipp]

Do you want to request a feature or report a bug?

bug

What is the current behavior?

We subscribe to a query using the subscribeToMore function of apollo.

We then use the updateQuery: (previousResult, ...args) => { ... } function to update the query when new subscription data comes in.

Our items always have an id and a version { id: string, _v: number, ... }. Merging is done by going through the query items and update the entry with the fitting id if the entry coming from the subscription has a higher version or inserting if the entry does not exist yet.

What we noticed is that if we are getting subscriptions e.g.

{ id: '1', _v: 4, name: 'Peter' }
{ id: '1', _v: 5, name: 'Bob' }

where the version is in correct order, everything is fine. If we get

{ id: '1', _v: 5, name: 'Bob' }
( waiting for some seconds )
{ id: '1', _v: 4, name: 'Peter' }

ordering incorrect, but with some time difference everything is fine too, Bob is displayed.

But, if we are getting subscriptions in rappid succession in wrong ordering

{ id: '1', _v: 5, name: 'Peter' }
{ id: '1', _v: 4, name: 'Bob' }

Bob is displayed. When debugging the updateQuery: (previousResult, ...args) => { function we saw that even though { id: '1', _v: 4, name: 'Bob' } is just coming in, it seems to already be part of the previousResult entry. Which is weird as it just came back from the subscription.

Is there a possibility that there is some caching going on inside the AwsAppsync subscription client ? Or are those subscription updates handled asyncronously ?

The reason why we are coming to this conclusion is that if we change the dataId to include the version, this issue dissappears:

dataIdFromObject: obj => {
  const { id, __typename, _v = '0' } = obj;

  if (id == null) return defaultDataIdFromObject(obj);

  return `${__typename}:${id}:${_v}`;
},

What is the expected behavior?

Subscriptions coming in in rappid succession should be handled in syncronously.

Which versions and which environment (browser, react-native, nodejs) / OS are affected by this issue? Did this work in previous versions?

We were able to reproduce this in Chrome and Firefox

[elorzafe]

@philiiiiiipp can you validate your update function to replace the value only if the version is greater than existing one?

[philiiiiiipp]

Yes, it does exactly that. It also works fine as long as we are not getting the items in rappid succession ( including if they are coming in different order ).