requestForDuplicatedObjects.swift

requestForDuplicatedObjects.swift

func requestForDuplicatedObjects(moc: NSManagedObjectContext) -> NSFetchRequest {
	let objectsToKeepRequest = NSFetchRequest(entityName: "Recipe")

	// Fetch object IDs representing objects to keep
	let ed = NSExpressionDescription()
	ed.expression = NSExpression.expressionForEvaludatedObject()
	ed.name = "SELF"
	ed.expressionResultType = .ObjectIDAttributeType
	objectsToKeepRequest.propertiesToFetch = [ed]

	// Group by source and exteralID
	objectsToKeepRequest.propertiesToGroupBy = ["source", "externalID"]
	objectsToKeepRequest.resultType = .DictionaryResultType

	let duplicateObjecsRequest = NSFetchRequest(entityName: "Recipe")

	// Set up a predicate matching all objects not returned by objectsToKeepRequest
	let fre = NSFetchRequestExpression.expressionForFetch(NSExpression(forConstantValue: objectsToKeepRequest), context: NSExpression(forConstantValue: moc), countOnly: false)
	duplicateObjectsRequest.predicate = NSPredicate(format: "NOT SELF IN %@", argumentArray: [fre])

	return duplicateObjectsRequest
}