Why is my relation-object reinitialized each time it is accessed? - ios

Question

I use Realm Swift 0.95.3. In my project I'm working with a contact (not with contacts AddressBook), which contain information about the name, last name, middle name, email, … and photograph.
I have created a subclass of Object called Contact. I understand that the image, or any other binary data, should not be stored in the Realm. Especially as my images could be large enough ~5 Mb.
In any case, I wanted to store the image in the file system, and Realm stores only a link to this image. I thought that in the future I may need to attach other files (audio, PDF, …) to subclasses of Object. So I decided to create a separate class File, which is inherited from Object. The whole structure looks like.
class File: Object {
dynamic var objectID = NSUUID().UUIDString
private var filePath: String {
let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
let documentsDirectory = paths[0] as NSString
return documentsDirectory.stringByAppendingPathComponent(objectID)
}
lazy var fileData: NSData? = {
return self.readFile()
}()
override static func primaryKey() -> String? {
return "objectID"
}
override static func ignoredProperties() -> [String] {
return ["fileData"]
}
override func copy() -> AnyObject {
let result = File(value: self)
result.objectID = NSUUID().UUIDString
result.fileData = fileData?.copy() as? NSData
return result
}
}
extension File {
//MARK:-
private func readFile() -> NSData? {
let lFilePath = filePath
print("Try to read file \(lFilePath)")
return NSData(contentsOfFile: lFilePath)
}
private func writeFileWithFileData() {
if let lFileData = fileData {
lFileData.writeToFile(filePath, atomically: true)
print("File \(filePath) was created")
} else {
removeFile()
}
}
private func removeFile() {
do {
try NSFileManager.defaultManager().removeItemAtPath(filePath)
print("File \(filePath) was removed")
} catch {
print(error)
}
}
}
As you can see, when trying to get the property fileData, data is received from the file system. Moreover fileData is declared with the keyword lazy, that is, I wish that the data is requested from disk to cache in this property. If this property is changed, the File object before saving to the database, I call writeFileWithFileData (), and data on the disk is overwritten. This system works as I need to, I to experiment. Then I created a Contact.
class Contact: Object {
dynamic var objectID = NSUUID().UUIDString
dynamic var firstName = ""
dynamic var lastName = ""
...
private dynamic var avatarFile: File?
var avatar: UIImage? {
get {
guard let imageData = avatarFile?.fileData else { return nil }
return UIImage(data: imageData)
}
set {
avatarFile = File()
guard let imageData = newValue else {
avatarFile?.fileData = nil
return
}
avatarFile?.fileData = UIImagePNGRepresentation(imageData)
}
}
override static func primaryKey() -> String? {
return "objectID"
}
override static func ignoredProperties() -> [String] {
return ["image"]
}
}
The problem is that when I choose a contact from the database, and am trying to get the avatar, then access to the file system occurs every time you access this property. That is, property fileData does not operate as lazy - as I thought at first. But then I looked at the memory address properties avatarFile, each time it is received, the address has changed. From this I can conclude that the object avatarFile is constantly requested from the database again, with any reference to this property. As a consequence, all its ignoredProperties are reset.
Why is the relation-object reinitialized each time it is accessed?
Share your opinion about my arch

Answer 1

It should be fine. Realm Objects are live links to their parent Realm object, not static copies, so their addresses do periodically change. This is normal, and the objects aren't getting re-allocated so you shouldn't see any memory issues here. As far as I'm aware, NSData itself is lazy, so the data won't actually be read until you explicitly request it.
Your architecture looks good! You're right in that it's usually not the best form to store file data directly inside a Realm file, but you've done a good job at making the Realm Object manage the external file data as if it was. :)