What is the best way to connect Realm and SwiftBon

Question

I love Realm and I love Bond. Both of them makes app creation a joy. So I was wondering what is the best way to connect Realm and Bond?
In Realm we can store basic types such as Int, String, e.g. But in Bond we work with Dynamics and Bonds. The only way that I found to connect Realm and Bond is following:

class TestObject: RLMObject {

   dynamic var rlmTitle: String = ""
   dynamic var rlmSubtitle: String = ""

   var title: Dynamic<String>
   var subtitle: Dynamic<String>

   private let titleBond: Bond<String>!
   private let subtitleBond: Bond<String>!

   init(title: String, subtitle: String) {
      self.title = Dynamic<String>(title)
      self.subtitle = Dynamic<String>(subtitle)

      super.init()

      self.titleBond = Bond<String>() { [unowned self] title in self.rlmTitle = title }
      self.subtitleBond = Bond<String>() { [unowned self] subtitle in self.rlmSubtitle = subtitle }

      self.title ->> titleBond
      self.subtitle ->> subtitleBond
   }
}

But it surely lacks simplicity and elegance and produces a lot of boiler code. Is there any way to do this better?

Answer 1

You could likely simplify the pattern you're using somewhat if you used default property values:

  class TestObject: RLMObject {

     dynamic var rlmTitle = ""
     dynamic var rlmSubtitle = ""

     var title: Dynamic<String>
     var subtitle: Dynamic<String>

     private let titleBond = Bond<String>() { [unowned self] title in self.rlmTitle = title }
     private let subtitleBond = Bond<String>() { [unowned self] subtitle in self.rlmSubtitle = subtitle }

     init(title: String, subtitle: String) {
        self.title = Dynamic<String>(title)
        self.subtitle = Dynamic<String>(subtitle)
        self.title ->> titleBond
        self.subtitle ->> subtitleBond

        super.init()
     }
  }

You could remove another two lines of code if Bond's ->> operator returned the left value so you could do self.title = Dynamic<String>(title) ->> titleBond.

But ultimately, until Swift has native language support for KVO or an equivalent observation mechanism, you're sadly going to have to write some amount of boilerplate.

Answer 2

With Realm supporting KVO and Bond 4, you can extend Realm objects to provide Observable variants. There is some boilerplate to it, but it's clean and without hacks.

class Dog: Object {
  dynamic var name = ""
  dynamic var birthdate = NSDate(timeIntervalSince1970: 1)
}

extension Dog {

  class ObservableDog {
    let name: Observable<String>
    let birthdate: Observable<NSDate>

    init(dog: Dog) {
      name = Observable(object: dog, keyPath: "name")
      birthdate = Observable(object: dog, keyPath: "birthdate")
    }
  }

  func observableVariant() -> Dog.ObservableDog {
    return ObservableDog(dog: self)
  }
}

Than you'll be able to do:

let myDog = Dog().observableVariant()

myDog.name.observe { newName in
  print(newName)
}

myDog.name.bindTo(nameLabel.bnd_text)

realm.write {
  myDog.name.value = "Jim"
}

Answer 3

I've been thinking about this for three days and came up with nearly perfect solution, which does not employ any boilerplate code. First of all I have created a super class for a realm model's wrapper:

class BondRealmBaseClass {

   private var realmModel: RLMObject!
   private let realm = RLMRealm.defaultRealm()
   private var bonds = NSMutableArray()

   init(){
      realmModel = createRealmModel()
      realm.beginWriteTransaction()
      realm.addObject(realmModel)
      realm.commitWriteTransaction()
      createBonds()
   }

   init(realmModel: RLMObject){
      self.realmModel = realmModel
      createBonds()
   }

   func createBondFrom<T>(from: Dynamic<T>, toModelKeyPath keyPath: String){
      from.value = realmModel.valueForKeyPath(keyPath) as T
      let bond = Bond<T>() { [unowned self] value in
         self.realm.beginWriteTransaction()
         self.realmModel.setValue(value as NSObject, forKey: keyPath)
         self.realm.commitWriteTransaction()
      }
      from ->| bond
      bonds.addObject(bond)
   }

   //MARK: - Should be overriden by super classes
   func createBonds(){ fatalError("should be implemented in supreclass") }
   func createRealmModel() -> RLMObject{ fatalError("should be implemented in supreclass") }
}

After that for each realm model I create two classes, first is the actual realm model, which stores all properties:

class RealmTodoModel: RLMObject { 
   dynamic var title = ""
   dynamic var date = NSDate()
}

and a second one is the wrapper around realm model:

class TodoModel : BondRealmBaseClass{
   let title = Dynamic("")
   let date = Dynamic(NSDate())

   override func createBonds(){
      createBondFrom(title, toModelKeyPath: "title")
      createBondFrom(date, toModelKeyPath: "date")
   }

   override func createRealmModel() -> RLMObject { return RealmTodoModel() }
}

And this two classes is actually all is needed to link Realm and Bond: creating new TodoModel will actually add to Realm new RealmTodoModel and all changes made with TodoModel's title and date will be automatically saved to corresponding Realm model!

EDIT

I added some functionality and posted this as a framework on GitHub. Here is the link.