How should I support offline mode using DynamoDB and iOS?

Question

This is a little bit of Parse fallout.

I'm moving an app to use DynamoDB but it doesn't seem to support any kind of offline mode.

How should I do this?

I'd like to use Realm but I'll end up having to manage synchronising and object <-> noSQL. Should I use a flag on a row to indicate it has been synced?

Should I try and keep the row flat like it is in Dynamo?

I don't think the sync part of Cognito is applicable here.

Answer 1

I haven't used DynamoDB before, but I just read through the iOS documentation on Amazon's website, and I THINK integrating the two should be possible, and relatively easy.

It looks like you define data models in DynamoDB the same way as Realm: create a subclass of AWSDynamoDBObjectModel and add your properties. As this is the case, as long as you created a Realm Object (or RLMObject in Objective-C) that had the same matching properties, you should (theoretically) be able to simply pass DynamoDB objects directly to Realm to be saved:

let realm = try! Realm()

try! realm.write {
    realm.create(MyRealmSubclass.self, value: MyDynamoDBObject, update: true)
}

Realm is very smart in being able to use KVC to see if any objects passed to it conform to the schema of its model objects and to automatically retrieve and save that information.

(NB: In order for update: to work properly, you'll also need to ensure your objects share a common primary key property as well).

From the sounds of it, if you're looking to then modify the locally saved data in Realm while the app is offline, and then push that modified data the device is back online, then it'll be up to you to convert the Realm model objects back into DynamoDB objects in order to be pushed back up to AWS.

You could certainly add additional properties to the Realm model, such as a boolean hasChanges flag, or a lastModifiedDate date object in order to be able to check that an offline object has changes that need uploading.

Let me know if you need any additional clarification!

(Full disclosure: I work for Realm.)