Expose “all changes since” via wordpress JSON api

Question

I'm struggling to find a solution to what I thought would be a common requirement so I'm hoping someone can help me with some pointers on what to search for/areas to explore.

Background

I'm building an iOS mobile app. I'm storing data locally using realm.io. The app is preinstalled with a snapshot of the content of a Wordpress mySQL database (it uses custom types). The content of the WP database is only written via the Wordpress install, the mobile app cannot write data.

Objective

So, I want to be able to check for changes since a given date (whenever the local database was last updated) and send the changed records to the mobile app (via the wp JSON api?).

I think I can fetch "posts since a date" but I need a full list of all create, update and delete operations since a given date.

Since the app is read-only I thought this type of one-way sync would be pretty straight forward but I can't find a common solution.

Any ideas to point me in the right direction would be great. Obviously, if anyone has any experience of doing this sort if thing with realm.io then that would be amazing :-)

Answer 1

Realm doesn't support yet any sort of synchronization mechanism across different files. We have an issue about that though, but you're likely searching rather for a solution in the immediate future.

Update: Realm launched the Realm Mobile Platform . This offers synchronization functionalities and would greatly simplify the solution for this use case.

You could use eg the server-side Node.js binding to pull new data from your MySQL Wordpress installation and push them to a global Realm served by the Realm Object Server. This can be read-only synchronized from the mobile apps, which would automatically receive the deltas and provide updated data to your users.

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Whatever mechanism you come up yourself though in the meantime, it would require that you have read-write access from your iOS application to the realm database, so that you can update it with new data.

Pushing changed records as you describe is likely not going to work.

Apple's Push Notification service (APNS), which is the only back communication channel that works when your app is in the background or suspended, allows you to send very small payloads. You would use that to signalize your iOS app, that something changed on the server-side and there is new data to load. You would then initiate a request to a JSON-based API, wait for the response, map the returned JSON to Realm objects and store them in your database.
You want probably read more in the "Downloading Content in the Background" section of background execution chapter in the official App Programming Guides for iOS.

While pre-seeding the database from the app bundle seems like a nice idea, because the user wouldn't need to wait initially after downloading the app, that will enlarge the app itself with data, which might become in the future completely irrelevant.