I saved datas in entity of CoreData. Also I can access data in CoreData through object.value(forKey:"attribute"). But, I don't know how to access data using index.
follow code is my access way
let context = getContext()
let fetchRequest : NSFetchRequest<Entity> = Entity.fetchRequest()
let result = try? context.fetch(fetchRequest){
for object in result
object.value(forKey:"attribute")...
...
}
}
How to access data in CoreData using index of data?
Your result is type of Array so you can access the object from result like result[0] and so on.
if index < result.count {
let obj = result[index]
}
If you want index from object, you can use index(of:) for that.
if let index = result.index(of: obj) {
print(index)
}
Related
I'm fairly new to CoreData, and I'm trying to make a game. I have a couple of questions I was hoping you guys could help me out with some guidance:
- does GameKit already have some sort of CoreData integrated in it? I am not sure if I am overthinking this CoreData stuff if there's already something that replaces it in GameKit.
. . .
Anyways, assuming the answer to the above question is "no. GameKit has nothing to save your game". I will proceed with my current "Save game" code which is the following:
func saveCurrentMatch()
{
/* CORE DATA STUFF:
FIRST NEED TO VERIFY IF THIS GAME HAS BEEN PREVIOUSLY SAVED, IF SO THEN UPDATE, ELSE JUST SAVE
Entity: MatchData
Attributes: scoreArray (String), playerArray (String), myScore (Int), matchID (Int), isWaiting (Bool), isRealTime (Bool), gameLog (String)
*/
let context = myAppDelegate.persistentContainer.viewContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "MatchData")
request.returnsObjectsAsFaults = false
do
{
let gamesInProgress = try context.fetch(request)
print (gamesInProgress.count)
if gamesInProgress.count > 0 //HERE CHANGE THIS TO LOOK FOR THE MATCH ID OF THIS GAME!!
{
gameExistsinCD = true
}
else
{
gameExistsinCD = false
}
}
catch
{
print ("Error Reading Data: \(error.localizedDescription)")
}
if gameExistsinCD
{
//CODE TO UPDATE MATCH INSTEAD OF SAVING NEW ONE
}
else
{
// CODE TO SAVE A NEW MATCH FOR THE FIRST TIME
let matchData = NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context)
matchData.setValue(isRealTime, forKey: "isRealTime")
matchData.setValue(currentScore?[0], forKey: "myScore")
matchData.setValue(currentScore?.map{String($0)}.joined(separator: "\t"), forKey: "scoreArray") // IS THIS CODE CORRECT? I'M TRYING TO SAVE AN ARRAY OF INTS INTO A SINGLE STRING
matchData.setValue(currentPlayers?.joined(separator: "\t"), forKey: "playerArray")
matchData.setValue(true, forKey: "isWaiting") //will change later to update accordingly.
matchData.setValue(matchID, forKey: "matchID")
matchData.setValue(gameLog, forKey: "gameLog")
do
{
try context.save()
print ("CoreData: Game Saved!")
}
catch
{
print ("Error Saving Data: \(error.localizedDescription)")
}
}
}
My main concern is on the fetch request, how do I check all the core-data if this match has already been saved? and if so, whats the code for updating an Entity instead of inserting a new one?
Any guidance is appreciated, thanks!
Don't let Core Data scare you. It can be a fine way to save local data and despite some comments, it is not slow when done right. In fact, Core Data can be quite fast.
You can simplify your code a lot by using your Object class in a more normal fashion instead of using setValue calls. Your create code can be changed to this:
// CODE TO SAVE A NEW MATCH FOR THE FIRST TIME
if let matchData = NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context) as? MatchData {
matchData.isRealTime = isRealTime
matchData.myScore = currentScore?[0]
matchData.scoreArray = currentScore?.map{String($0)}.joined(separator: "\t") // IS THIS CODE CORRECT? I'M TRYING TO SAVE AN ARRAY OF INTS INTO A SINGLE STRING
// You can certainly save it this way and code it in and out. A better alternative is to have a child relationship to another managed object class that has the scores.
matchData.playerArray = currentPlayers?.joined(separator: "\t")
matchData.isWaiting = true
matchData.matchID = matchID
matchData.gameLog = gameLog
}
This is a much more readable and normal way to set your object properties. Any time you change a property on a core data managed object then it will get saved the next time you save the context.
As far as finding a current record that matches the ID, I like to add classes like that to my Managed Object class itself:
class func findByID(_ matchID: String) -> MatchData? {
let myAppDelegate = UIApplication.shared.delegate as! AppDelegate
let context = myAppDelegate.persistentContainer.viewContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "MatchData")
let idPredicate = NSPredicate(format: "matchID = \(matchID)", argumentArray: nil)
request.predicate = idPredicate
var result: [AnyObject]?
var matchData: MatchData? = nil
do {
result = try context.fetch(request)
} catch let error as NSError {
NSLog("Error getting match: \(error)")
result = nil
}
if result != nil {
for resultItem : AnyObject in result! {
matchData = resultItem as? MatchData
}
}
return matchData
}
Then any place you need the match data by ID you can call the class function:
if let matchData = MatchData.findByID("SomeMatchID") {
// Match exists
}
Core data is basically wrapper around SQL database. It is very efficient when you are working with high volume of data that need to be stored. So please consider either you had such requirements, otherwise perhaps it can be wise to store data in user defaults, or settings.
If it is, there is few things you need to know.
It is very useful to create you own model classes. Open core data model file, open "Editor/Create NSManagedObject subclass". It will allow you to refer direct properties, instead of KVC(setValue:forKey:).
Alway mind what thread you are working in. It is unsafe to work with objects, created in other threads.
Your gamesInProgress contains array of objects you fetched from your database.
So basically instead of
if gameExistsinCD
{
//CODE TO UPDATE MATCH INSTEAD OF SAVING NEW ONE
}
else
{
// CODE TO SAVE A NEW MATCH FOR THE FIRST TIME
let matchData = NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context)
matchData.setValue(isRealTime, forKey: "isRealTime")
<...>
you can do
let matchData = (gamesInProgress.first ??
NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context)) as! <YouEntityClass>
matchData.isRealTime = isRealTime
<...>
PS: https://www.raywenderlich.com/173972/getting-started-with-core-data-tutorial-2
I have a fetch to core data that returns a NSManagedObject like so
let results = try context.fetch(data);
let resultset = results as! [NSManagedObject];
I have a string array created like so:
var db: [String] = [];
My core data has a column called blogs.
How do I get that entire column into my db variable?
Blogs column is a string.
New to core data too.
Use the map function
let results = try context.fetch(data) as! [NSManagedObject]
db = results.map { $0.value(forKey: "blogs") as! String }
or – preferable – if your are using NSManagedObject subclass and generic entity
let results = try context.fetch(data)
db = results.map { $0.blogs }
And remove the semicolons in your code by the way...
in my class I have a method to extract data from coredata. But I have a problem: I need to convert the result to an array, because then I'll have to use that array in an other class.
The method is:
func loadQuestion() -> NSArray{
let fetchRequest: NSFetchRequest<Questions> = Questions.fetchRequest()
do {
let array = try self.context.fetch(fetchRequest) as NSArray
guard array.count > 0 else { print("[EHY!] Non ci sono elementi da leggere "); return array }
return array
} catch let errore {
print("error FetchRequest")
}
return list
}
I can't figure out how to convert the variable array?
The result (wrong)
Edit: I write this because I want to convert the result of fetch into
an array, so you can switch to another class
fetch returns an (optional) array, so all you need to do is return that from your function. Since fetch throws your function should either throw or at least return an optional, as the fetch can fail.
In Swift it is very rarely necessary to use NSArray; a properly typed Swift array will make your code clearer and safer. Since CoreData in Swift supports Generics, fetch will return the appropriate array type automatically, based on your NSFetchRequest. Even if you are calling this function from Objective-C, it is best to let the compiler bridge the Swift array to an NSArray for you
Finally, you are using guard incorrectly; you attempt to return array in the case where it has 0 items, otherwise you return some variable list which isn't declared in the code you have shown.
func loadQuestion() -> [Questions]? {
let fetchRequest: NSFetchRequest<Questions> = Questions.fetchRequest()
do {
let array = try self.context.fetch(fetchRequest) as [Questions]
return array
} catch let errore {
print("error FetchRequest \(errore)")
}
return nil
}
I have a tableView and that tableview is being populated with data from Coredata. The data breaks down like this.
Entity - Person
Entity - Statement
The statement entity has an attribute called amountOwed and it is of decimal type.
The relationships is that a person can have many statements, but each statement belongs to a single person.
Here is the path of the data that I would like to add up. Person > Statement > AmountOwed.
In the tableView function I have a let that represents the Person entity.
let person = fetchedResultsController.object(at: indexPath)
I know its working because I can print out the persons name like so
print(person.name) // Bob
What I want to be able to do is add up all the amountOwed attributes for each Person inside the Statement entity and display them on a cell.
I have been trying to follow an example of calculated fetches but I seem to not quiet understand how to target my Statements Entities which are linked to each Person entity.
let fetchRequest = NSFetchRequest<NSDictionary>(entityName:"statement")
fetchRequest.resultType = .dictionaryResultType
let sumExpressionDesc = NSExpressionDescription()
sumExpressionDesc.name = "sumDeals"
let specialCountExp = NSExpression(forKeyPath: #keyPath(Person.statement[indexPath].amountOwed))
sumExpressionDesc.expression = NSExpression(forFunction: "sum:", arguments: [specialCountExp])
sumExpressionDesc.expressionResultsType = .interger32AttributeType
fetchRequest.propertiesToFetch = [sumExpressionDesc]
do{
let results = try coreDataStack.managedContext.fetch(fetchRequest)
let resultDict = results.first!
let numDeals = resultDict["sumDeals"]
print(numDeals!)
}
catch let error as NSError{
print("Count not fetched \(error), \(error.userInfo)")
}
Do I need to fetch a Statement entity or should I just use the FetchedREsultsController? If I do use my fetchedResultsController does the keypath to the Statement Entity look like this
person[indexPath].statement.amountOwed
You can do that in one line. If the relationship from Person to Statement is called statements, you get the total of the amounts with
let amountTotal = newPerson.value(forKeyPath: "statements.#sum.amount") as? Int64
Change the downcast at the end from Int64 to whatever is appropriate for your amount attribute-- Double or whatever.
OK on your People+CoreDataClass add:
var totalOwed: Float {
get {
var value: Float = 0
if let statements = self.statements.allObjects() as? [Statement] {
for s in statements {
value = value + s.sum
}
}
return value
}
}
And remove all the code from your fetch that is unnecessary
I did manage to do this by making a function with a loop that checks the attribute to a string. But i'm looking for a better way to do this.
In sql I do this:
Select * WHERE "attribute" == "string"
Is there a method to do this in swift?
My function looks like this:
func tableData()
{
let objects = retrieveValues("JobTime") //Retrieve a NSMutableArray
if !objects.isEmpty
{
for var index = 0; index < objects.count; ++index
{
if objects[index].valueForKey("jobTitle") as? String == transferTitle
{
print("Job title matched: \(index)")
}
else
{
print("Nothing here!")
}
}
}
}
In order to perform fetch request in CoreData you have to initialise NSFetchRequest class. In order to specify in what kind of entities you are interested you create NSPredicate class. It gives you ability to specify pretty advanced queries. In most cases the simplest way to create NSPredicate is by using format string - details about the syntax can be found Apple's Predicate Format String Syntax document.
You can find example of how you can perform fetch request in CoreData (and Swift) below.
let managedObjectContext: NSManagedObjectContext
let predicate = NSPredicate(format: "jobTitle == %#", "Programmer")
let fetchRequest = NSFetchRequest.init(entityName: "People")
fetchRequest.predicate = predicate
//fetchRequest.sortDescriptors = [] //optionally you can specify the order in which entities should ordered after fetch finishes
let results = managedObjectContext.executeFetchRequest(fetchRequest)
You can pass the query to CoreData and only retrieve what you want. The NSManagedObjectContext class has a executeFetchRequest method that you call to retrieve data from the database. You pass NSFetchRequest object to it. That object contains a NSPredicate, which defines your query.