Realm Migration doesn't work

I had a similar issue happening where my app would crash despite the fact that I added the default migration code in didFinishLaunchingWithOptions

The problem was that I was indeed initializing an instance of Realm in my first view controller as a class level property. So removing that class level realm object from my first ViewController fixed the issue.

import UIKit
import RealmSwift

class ViewController: UIViewController{
  let db = try! Realm() // Removing this solved my issue

  func doSomething(){
    let db = try! Realm() // Placed this here instead
  }
}

I instead created the object inside the function that needed it, which is a better approach anyway.

As long as you're in local development only, I'd recommend to reset your Realm database instead of doing a migration. Migrations are the way to go, if you have already shipped a version of your app with another schema and want to keep user data.

You can delete the database by deleting the app from the simulator or the device. Alternatively you can use NSFileManager to delete the Realm file before accessing the database.

let defaultPath = Realm.Configuration.defaultConfiguration.path!
try NSFileManager.defaultManager().removeItemAtPath(defaultPath)

Make sure you don't try to instantiate instance of Realm() before migration config is set in application(application:didFinishLaunchingWithOptions:). When it crashes check execution stack to find which instance raised exception. I had the same error, in my case Realm instance in one of my view controllers were instantiated before migration block was set.

Good luck