Core Data: Beyond the Basics

Jul 26 2022 · Swift 5.5, iOS 15, Xcode 13.3.1

Part 2: Advanced Core Data

15. Saving Launches with Batch Operations

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Previous episode: 14. Asynchronously Loading Launches Next episode: 16. Saving Launches Concurrently

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Now that you have data from the SpaceX API, it’s time to put that data in the database. There are two techniques you’ll use together to do this: one is batch operations, which you’ll learn about in this episode, and asynchronous Core Data, which you’ll learn about in the next episode.

private func createBatchInsertLaunchRequest(from launchCollection: [SpaceXLaunchJSON]) -> NSBatchInsertRequest {

}

var index = 0
let total = launchCollection.count

let batchInsertRequest = NSBatchInsertRequest(entity:  
  SpaceXLaunch.entity(), dictionaryHandler: { dictionary in
  guard index < total else { return true }
  dictionary.addEntries(from: launchCollection[index].dictionaryValue as [AnyHashable: Any])
    index += 1
    return false
  })
return batchInsertRequest

var dictionaryValue: [String: Any] {
	[
	  "reused": reused as Any,
	  "recoveryAttempt": recoveryAttempt as Any,
	  "recovered": recovered as Any,
	  "ships": ships,
	  "id": id
	]
}

protocol BatchInsertable: Codable {
  var dictionaryValue: [String: Any] { get }
}

let taskContext = container.viewContext

let fairings = launchCollection.map { ($0.id, $0.fairings) }
let links = launchCollection.map { ($0.id, $0.links) }

var list: SpaceXLaunchList!
let fetchRequest = SpaceXLaunchList.fetchRequest()
fetchRequest.predicate = NSPredicate(format: "title == %@", listName)
let results = try taskContext.fetch(fetchRequest)
if let fetchedList = results.first {
	list = fetchedList
}

let batchInsertRequest = createBatchInsertLaunchRequest(from: launchCollection)
if let fetchResult = try?
  taskContext.execute(batchInsertRequest),
  let batchInsertResult = fetchResult as? NSBatchInsertResult,
  let success = batchInsertResult.result as? Bool, 
  success {
	  return
	} else {
		throw LaunchError.batchInsertError
	}

private func createBatchInsertRelationshipRequest<T: BatchInsertable, E: NSManagedObject>(from relationshipCollection: [(String, T?)], for type: E.Type) -> NSBatchInsertRequest {
	var index = 0
	let total = relationshipCollection.count
	
	// Provide one dictionary at a time when the closure is called.
	let batchInsertRequest = NSBatchInsertRequest(entity: E.entity(), dictionaryHandler: { dictionary in
	  guard index < total else { return true }
	  guard let value = relationshipCollection[index].1 else { index += 1; return false }
	  dictionary.addEntries(from: value.dictionaryValue as [AnyHashable: Any])
	  index += 1
	  return false
	})
	
	return batchInsertRequest
}

let batchInsertRequest2 = createBatchInsertRelationshipRequest(from: fairings, for: SpaceXFairings.self)
if let fetchResult = try? taskContext.execute(batchInsertRequest2),
let batchInsertResult = fetchResult as? NSBatchInsertResult,
let success = batchInsertResult.result as? Bool, success {
  return
} else {
throw LaunchError.batchInsertError
}

// Setup the fairing relationships
for (id, fairing) in fairings {
	guard let fairing = fairing else { continue }
	let fairingFetchRequest = SpaceXFairings.fetchRequest()
	fairingFetchRequest.predicate = NSPredicate(format: "id == %@", argumentArray: [fairing.id])
	
	let launchFetchRequest = SpaceXLaunch.fetchRequest()
	launchFetchRequest.predicate = NSPredicate(format: "id == %@", argumentArray: [id])
	
	let returnedFairing = try taskContext.fetch(fairingFetchRequest) as [SpaceXFairings]
	let launch = try taskContext.fetch(launchFetchRequest) as [SpaceXLaunch]
	guard !returnedFairing.isEmpty, !launch.isEmpty else { continue }
	let matchedFairing = returnedFairing[0]
	let matchedLaunch = launch[0]
	matchedFairing.launch = matchedLaunch
}
try taskContext.save()

// Use a batch insert request to add the links
let batchInsertRequest3 = createBatchInsertRelationshipRequest(from: links, for: SpaceXLinks.self)
if let fetchResult = try? taskContext.execute(batchInsertRequest3),
let batchInsertResult = fetchResult as? NSBatchInsertResult,
let success = batchInsertResult.result as? Bool, success {
  return
} else {
	throw LaunchError.batchInsertError
}

// Setup the link relationships
for (id, links) in links {
	let linksFetchRequest = SpaceXLinks.fetchRequest()
	linksFetchRequest.predicate = NSPredicate(format: "id == %@", argumentArray: [links.id])
	
	let launchFetchRequest = SpaceXLaunch.fetchRequest()
	launchFetchRequest.predicate = NSPredicate(format: "id == %@", argumentArray: [id])
	
	let returnedLinks = try taskContext.fetch(linksFetchRequest) as [SpaceXLinks]
	let launch = try taskContext.fetch(launchFetchRequest) as [SpaceXLaunch]
	guard !returnedLinks.isEmpty, !launch.isEmpty else { continue }
	returnedLinks[0].launch = launch[0]
	launch[0].addToSpaceXList(list)
}
try taskContext.save()