apollo-ios: Query watcher not being called when cache is updated on an element by another query/subscription/mutation

Bug report

Query watcher not being called when cache is updated on an element of a collection that is added after calling watch

Versions

Please fill in the versions you’re currently using:

• apollo-ios SDK version: 0.34.0
• Xcode version: 12.0.1
• Swift version: 5.3

Steps to reproduce

I’ve been trying a lot of things on that one and wasn’t able to find a way to fix my problem. So in my app I’m having a list of conversations, so I’m creating a watch on a query that returns the list of conversations, this is something like that:

user {
    uuid
    firstName
    lastName
    conversations {
        uuid
        unreadMessagesCount
    }
}

In the app we use the uuid key to handle cache, so we make sure to always pass uuid in our queries to automatically handle cache update.

So the role of the watcher I’m talking about is both to update existing conversations and also be able to catch when a new conversation is created (it can happen and not be initiated by the user, we then trigger an event from the backend that is listen from a subscription in the app). When this event happens it returns something like that

event {
     newConversation {
          conversation {
               uuid
               unreadMessagesCount
               // This is the part that adds the new conversation to the existing ones of the users in the cache
               user {
                    uuid
                    conversations {
                          uuid
                          unreadMessagesCount
                    }
               } 
          }
     }
}

It works great, meaning that when this event happens, the watcher is being called with the newly created conversation, but the issue is that any new cache update for that specific conversation doesn’t trigger the watcher again.

After investigating a bit, I realised that the cache is being updated because if I’m adding 3 new messages into the new conversation (setting the unreadMessagesCount to 3), the watcher doesn’t get called but then if I add 1 new message into an old one, the watcher is being called with both the new message on the old conversation and the 3 new on the new one.

So it really seems like watch is not being called again for changes on an item that wasn’t in a collection when the watch was initially made. I’ve also take a look at https://github.com/apollographql/apollo-ios/issues/281 and making a fetch on the same query again after the event doesn’t fix the issue.

Let me know if I’m not clear on something as the whole thing is a bit complicated to explain.