How to create a database using Parse that will work offline? - ios

Question

My app is a directory with basic things like phone numbers and locations. There's going to be many entries and I will have to update the database on a weekly basis and I don't want to rely on my users to update their app using the App store, so I want the data to be updated whenever they connect to the internet, but I want all of the data stored locally so they can use it even if they don't have internet access. For my first app, it's proving to be quite tricky :)
I think I'll have to use Parse so I can update the database whenever I need to, along with something like Realm (https://realm.io/) or Core Data (hopefully not Core Data :( ). I read about Parse's Local DataStore, and if there's a way to make it work for my needs I'd definitely use it. I like the simplicity of Realm though and if I there's a way to make it work with Parse, that would be the route I'd want to take.
Can somebody show me an example on how they might go about doing this? If the PFObject or RLMObject is called person and has two strings (phone number and name, how would you get that from Parse.com to the device (local storage)?
This is an extra and I don't even know if it's possible*
While the app is downloading from the App Store, could it download the data from Parse? As in, the second the user opens the app, even if they no longer have internet access, the data is locally stored and usable to them.
(I only know Swift but may be able to understand obj-c if anybody cares to show me some code snippets)
Any help at all would be greatly appreciated :)

Answer 1

Joe from Realm here.
First to retreive an object from Parse you will need to do this:
var query = PFQuery(className:"GameScore")
query.whereKey("playerName", equalTo:"Sean Plott")
query.findObjectsInBackgroundWithBlock {
(objects: [AnyObject]?, error: NSError?) -> Void in
if error == nil {
// The find succeeded.
println("Successfully retrieved \(objects!.count) scores.")
// Do something with the found objects
if let objects = objects as? [PFObject] {
for object in objects {
println(object.objectId)
}
}
} else {
// Log details of the failure
println("Error: \(error!) \(error!.userInfo!)")
}
}
You can read more about this here
Once you retrieve your objects, I would loop through them as you see here
for object in objects {
println(object.objectId)
}
And then I would use Realm's Realm().create(_:value:update:)(shown in code below). You need to make sure you have a primary key to use this though (I would use parse's objectId as the primary key in Realm). Here is how you set a primary key in Realm.
An example of how I would import them into Realm would be something like this (Where Venue is the class of the way the object is stored in Realm):
let realm = Realm()
realm.write {
for object in objects {
realm.create(Venue.self, value: object, update: true)
}
}
You can read more about importing here
Lastly the logic of when you do this is up to you. You could do it each time the person opens the app. One thing with syncing local databases with the ones on the server is that it's good to just check another Table maybe called LastUpdated. This table will let you know if you need to update your local database. Overall it's a very manual process but it depends on the situation and how you want to structure your app.