I'm building an app that gets a lot of data from a web service. The app consists of different entries that have relationships to each other. Let's make an example and say I'm building a TV show tracking app, all the data is coming from the web service, but I want to mark episodes as watched, which is a custom property on one entry so far. All of this gets save in Core Data. I have these entries:
- Show ⇒ has many seasons and episodes
- Season ⇒ has many episodes and one show
- Episode ⇒ has one show and one season
The main part I'm currently struggling with is how I can best update all of these entries when the web service has an updated version of the data (maybe the show got a new season or some wrong data got fixed). At this point, the only custom property on these entries which differs from the data the web service provides is the watched attribute I created on the Episode entry.
So far I tried different ways, like removing the old data and just adding the new one (the custom watched attribute is a problem here) and I also looked into merge policies like NSMergeByPropertyObjectTrumpMergePolicy but this doesn't play nice with relationships and I got to a roadblock there.
Is there a better way or best practice how to solve this?