Versioning and Migration - Core Data - page 147

let modelURL = NSBundle . mainBundle (). URLForResource (name,
withExtension: "mom" ,
subdirectory: "UnCloudNotesDataModel.momd" )
return NSManagedObjectModel (contentsOfURL: modelURL!)
}
}
The first method will return all model versions for a given name. The second
method will return a specific instance of NSManagedObjectModel . Usually, Core Data
will give you the most recent data model version, but this method will let you dig
inside for a specific version.
Note : When Xcode compiles your app into its app bundle, it will also compile
your data models. The app bundle will have at its root a .momd folder that
contains .mom files. MOM or Managed Object Model files are the compiled
versions of .xcdatamodel files. You'll have a .mom for each data model
version.
To use this method, add the following method inside the class extension:
class func version1() -> NSManagedObjectModel {
return uncloudNotesModelNamed ( "UnCloudNotesDataModel" )
}
This method will return the first version of the data model. That takes care of
getting the model, but what about checking the version of a model? Add the
following method to the class extension:
func isVersion1() -> Bool {
return self == self . dynamicType . version1 ()
}
You'll be able to call this method to check whether it is from version 1 when you
have a NSManagedObjectModel instance.
Next, add similar methods for versions 2 to 4 to the class extension:
class func version2() -> NSManagedObjectModel {
return uncloudNotesModelNamed ( "UnCloudNotesDataModel v2" )
}
func isVersion2() -> Bool {
return self == self . dynamicType . version2 ()
}
class func version3() -> NSManagedObjectModel {
return uncloudNotesModelNamed ( "UnCloudNotesDataModel v3" )
}