CoreData FetchRequest problems - ios

I'm teaching myself to programme and have thought up this project for myself to learn. I'm having trouble with my code, I was able to save it correctly and load the first state population TVC. However, I'm having problems with the state and number of animals per state TVC. I want to total it per a state. So I would be adding the dogs and cats population together and get the total per a state, but it brings Alabama separately with two different population, can someone help me with this please.
the model below shows how I want it, I'm able to output to State Population correctly but now the second one.
What my code is doing for the second one is that it's getting the data from coredata but I'm using sort descriptor because I don't know any other way to pull the data.
var totalEntries : Int = 0
let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
var frc : NSFetchedResultsController = NSFetchedResultsController()
func fetchRequest() -> NSFetchRequest {
let fetchRequest = NSFetchRequest(entityName: "Animals")
let sortDescriptor = NSSortDescriptor(key: "state", ascending: true)
fetchRequest.sortDescriptors = [sortDescriptor]
return fetchRequest
}
func getFRC() -> NSFetchedResultsController {
frc = NSFetchedResultsController(fetchRequest: fetchRequest(), managedObjectContext: moc, sectionNameKeyPath: nil, cacheName: nil)
return frc
}
override func viewDidLoad() {
super.viewDidLoad()
frc = getFRC()
frc.delegate = self
do {
try frc.performFetch()
} catch {
print("Failed to fetch data")
return
}
totalEntries = moc.countForFetchRequest(fetchRequest(), error: nil) as Int!
self.tableView.reloadData()
}
override func viewDidAppear(animated: Bool) {
frc = getFRC()
frc.delegate = self
do {
try frc.performFetch()
} catch {
print("Failed to fetch data")
return
}
totalEntries = moc.countForFetchRequest(fetchRequest(), error: nil) as Int!
self.tableView.reloadData()
}

Your problem is the fetched results controllers aren't designed to show aggregated fetch results like you desire, hence you see all the underlying data instead of the aggregate.
You could use the FRC if you cheat... Set the section name of the FRC to the state name, then you will have one section in the table per state. In the table delegate return 1 for the number of rows in each section. When configuring the cell use KVC to #sum the populations of all of the animals in that state (the rows for that section as understood by the FRC).
This is a memory and runtime inefficient solution... It could be improved by caching the calculated sums, but you're adding logic on top of bad design then.
The correct approach would be to abandon the FRC and use a simple array of dictionaries. This would be generated by changing your fetch request to return dictionary type and configuring it to calculate the sums for you. That's done with an expression something like:
NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];
expressionDescription.name = #"sumOfPopulations";
expressionDescription.expression = [NSExpression expressionForKeyPath:#"#sum.population"];
expressionDescription.expressionResultType = NSDecimalAttributeType;

Related

NSFetchedResultsController not working with transient property for sectionNameKeyPath

Working fine in Swift 3 with Xcode8.3
I have a project ongoing which has core data for saving messages.
It sorts messages according to time and sections them according to day.
Here's how:
let request = NSFetchRequest(entityName: "Message")
let sortDiscriptor = NSSortDescriptor(key: "time", ascending: true)
request.sortDescriptors = [sortDiscriptor]
fetchedResultsController = NSFetchedResultsController(fetchRequest: request, managedObjectContext: mainThreadMOC, sectionNameKeyPath: "sectionTitle", cacheName: nil)
fetchedResultsController.delegate = self
do {
try fetchedResultsController.performFetch()
} catch {
fatalError("Failed to initialize FetchedResultsController: \(error)")
}
Here is transient property:
var sectionTitle: String? {
//this is **transient** property
//to set it as transient, check mark the box with same name in data model
return time!.getTimeStrWithDayPrecision()
}
Using it as:
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
let sectionInfo = fetchedResultsController.sections![section]
let n = sectionInfo.numberOfObjects
return n
}
It always gives 0 sections and sectionTitle property never getting called.
This setup was/is working correctly with Swift3 in Xcode8.3.
Even this is working with Swift3.2 in Xcode9-beta.
But if I switch to Swift4 in Xcode9-beta, it's not working.
Add #objc to the transient property, so:
#objc var sectionTitle: String? {
//this is **transient** property
//to set it as transient, check mark the box with same name in data model
return time!.getTimeStrWithDayPrecision()
}
I just switched 'Swift 3 #objc inference' in the build settings to 'on' and all works fine again.

NSFetchResultController loading all messages at once, fetchbatchsize is not fixing it

I am at the stage of optimizing my core data code,
I am making a messaging app, and I only want to load 50 messages at a time.
However, looking at the timeprofile Data below, the fetchrequest loads all the messages at once. Afterwards, it loads all the messages in batches of 50 without even scrolling. So it's like not even doing anything.
Any help would be greatly appreciated.
lazy var fetchedResultsControler: NSFetchedResultsController = {
let fetchRequest = NSFetchRequest(entityName: "Mesages")
fetchRequest.fetchBatchSize = 20
fetchRequest.sortDescriptors = [NSSortDescriptor(key: "timestamp", ascending: true)]
fetchRequest.predicate = NSPredicate(format: "user.id = %#", self.friend!.id!)
let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
let frc = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: moc, sectionNameKeyPath: nil, cacheName: nil)
frc.delegate = self
return frc
}()
override func viewDidLoad() {
super.viewDidLoad()
do {
try fetchedResultsControler.performFetch()
} catch let err {
print(err)
}
self.fetchData = fetchedResultsControler.fetchedObjects as! [Mesages]}
This is the CoreData time profiling data:
That's correct behavior, per the NSFetchRequest documentation:
When the fetch is executed, the entire request is evaluated and the identities of all matching objects recorded, but no more than batchSize objects’ data will be fetched from the persistent store at a time. The array returned from executing the request will be a proxy object that transparently faults batches on demand. (In database terms, this is an in-memory cursor.
If, instead, you want explicit control of the fetch grouping, use a combination of fetchLimit and fetchBatchSize instead. But at that point you're fighting the features of NSFetchedResultsController.
What are you really trying to do with the fetchData array?

How to take Core Data and Filter it with NSPredicate Swift

I am currently learn and creating a basic decision app. The basics of the app is to take user input for a category they would like to do and then all the things that want to fill that category with.
Now I am wanting to display the results on a table view which works but I also what to click on each individual category that they recently used and be able to see the things that they placed under ever category. I was getting everything that was being save to the Core Data but now I am trying to use NSPredicate to filter out what I need. When I run the App there is nothing in the table view.
mainName I have passed in from a different view controller to capture and set what the name of the category was to help filter the data. I was trying to use it in the predicate as a filter.
I don't know if what I am doing is right but help would be great. This is independent study project I am doing to help finish my degree and everything I know is self taught so far. If what I have is completely wrong please tell me. This is just one of the hundreds of different ways I have tried to get this right.
#IBOutlet weak var tableview: UITableView!
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return whats.count
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("cell")! as UITableViewCell
let Doing = whats[indexPath.row]
cell.textLabel!.text = Doing.valueForKey("what") as? String
return cell
}
func loadData(){
let appDelegate = UIApplication.sharedApplication().delegate as? AppDelegate
if let context = appDelegate?.managedObjectContext{
let fetchRequest = NSFetchRequest(entityName: "Doing")
let namePredicate = NSPredicate(format: "namesR.noun = '\(mainName)'")
(whats as NSArray).filteredArrayUsingPredicate(namePredicate)
fetchRequest.predicate = namePredicate
do {
let results =
try context.executeFetchRequest(fetchRequest)
whats = results as! [NSManagedObject]
} catch let error as NSError {
print("Could not fetch \(error), \(error.userInfo)")
}
}
}
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
}
override func viewDidLoad() {
super.viewDidLoad()
loadData()
}
If you want use Core Data in your tableView based app? You can use NSFetchedResultsController class and their delegate protocol methods. This class specially designed for a tableView!
Official Documentation for NSFetchedResultsController class
From my understanding, you're saying you have a Category entity and an Item entity with many Item for each Category. In that case, in the view controller where you want to display the Items, you need to have a Category variable to use in your predicate so that you only get back the Items associated with that Category.
class ItemsTableVC {
var category: Category!
lazy var fetchedResultsController: NSFetchedResultsController = {
let fetchRequest = NSFetchRequest(entityName: "Item")
fetchRequest.sortDescriptors = []
fetchRequest.predicate = NSPredicate(format: "category == %#", self.category)
let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.sharedContext, sectionNameKeyPath: nil, cacheName: nil)
fetchedResultsController.delegate = self
return fetchedResultsController
}()
}

Display results from CoreData using NSPredicate in Swift

I have the following code in my viewDidLoad()
fetchedResultsController = NSFetchedResultsController(fetchRequest: FetchRequest("Teams", key: "team_name"), managedObjectContext: managedObjectContext!, sectionNameKeyPath: nil, cacheName: nil)
fetchedResultsController?.delegate = self
fetchedResultsController?.performFetch(nil)
and this code in my TableView cellForRowAtIndex:
var cell = teamView.dequeueReusableCellWithIdentifier("team_cell", forIndexPath: indexPath) as! TeamCellSettings
if let cellContact = fetchedResultsController?.objectAtIndexPath(indexPath) as? Team {
//create cell here
}
return cell
I have read online on how to use NSPredicate, but I cannot seem to get it to work. My goal is to use a segmented control to switch between the results displayed in the UITableView based off of the contents of a row's attribute. So if my entity X had an attribute named A, A would store either a 1 or a 0, so basically I need the segmented control to switch between all the results containing a 1 in attribute A or a 0 in attribute A
My creative writing skills are not the best. Hope you can understand my goal. Thank you.
The predicate needs to be added to the fetch request, for example:
let request = NSFetchRequest(entityName: "Your entity name")
let predicate = NSPredicate(format: "A == %d", 1)
request.predicate = predicate
fetchedResultsController = NSFetchedResultsController(
fetchRequest: request,
managedObjectContext: managedObjectContext!,
sectionNameKeyPath: nil,
cacheName: nil)
What goes to the predicate depends on your goals. In a next step you will need to update the fetch request and reload the data as you change the selected item in the segmented control. In your IBAction that is called when the segmented control changes, get sender.selectedSegmentIndex and create the new predicate based on the index.
The code to refetch will look something like this:
Swift 2
fetchedResultsController.fetchRequest.predicate = NSPredicate(format: "A = %d", some_int_goes_here)
do {
try fetchedResultsController.performFetch()
}
catch let error as NSError {
NSLog("%#", error.localizedDescription)
}
catch {
fatalError()
}
tableView.reloadData()
If you do Swift 1.2, omit the error handling, of course, something like this:
fetchedResultsController.fetchRequest.predicate = NSPredicate(format: "A = %d", some_int_goes_here)
fetchedResultsController.performFetch()
tableView.reloadData()

Re-order cells in UITableView with swift and fetchedResultsController

I have a UITableView in swift where the app allows users to re-order the cells, but it keeps crashing during the re-order.
I have this data model:
class Person: NSManagedObject {
#NSManaged var name: String
#NSManaged var mood: String
}
I have setup a bool variable to check when the user hits the edit button to see if the tableview.setEdititing is set to true, because this indicates a change in order is about to happen:
var userDrivenDataChange : Bool = false
Then for each of the fetched results controller delegate methods before I go ahead I always check if there are user driven changees to the object - for example...
func controllerWillChangeContent(controller: NSFetchedResultsController) {
if userDrivenDataChange{
return
}
tblView.beginUpdates()
}
Now, this is the bit I'm really struggling with...
In the moveRowAtIndexPath function, my logic is to get the object the user has just moved, and then get the section that the user wants to move the line to. Then create a new Person NSManagedObject but set its "mood" field to the new section name, then delete the object at the old indexPath.
func tableView(tableView: UITableView, moveRowAtIndexPath sourceIndexPath: NSIndexPath, toIndexPath destinationIndexPath: NSIndexPath) {
userDrivenDataChange = true
var context = (UIApplication.sharedApplication().delegate as AppDelegate).managedObjectContext!
var entity = NSEntityDescription.entityForName("Person", inManagedObjectContext: context)
var secInfo = fetchedResultController.sections![destinationIndexPath.section] as NSFetchedResultsSectionInfo
var personToAmend = fetchedResultController.objectAtIndexPath(sourceIndexPath) as Person
var copyOfPerson = Person(entity: entity!, insertIntoManagedObjectContext: context)
copyOfPerson.name = personToAmend.name
copyOfPerson.mood = secInfo.name!
context.deleteObject(personToAmend)
var err : NSError?
if !context.save(&err){
println(err)
}
userDrivenDataChange = false
}
So this doesn't work, honestly can't figure out why!
Any help would be greatly appreciated!
Thanks,
Jamie
p.s. Just incase you need to see it, my fetched results controller is:
lazy var fetchedResultController : NSFetchedResultsController = {
let fetchRequest = NSFetchRequest(entityName: "Person")
let context = (UIApplication.sharedApplication().delegate as AppDelegate).managedObjectContext!
let sort = NSSortDescriptor(key: "mood", ascending: true)
fetchRequest.sortDescriptors = [sort]
let frc = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: "mood", cacheName: nil)
frc.delegate = self
return frc
}()
----EDIT:
When a user reorders rows from one section to another, the fetchedResultsController always adds the row to the beginning of the section instead of the actual index path represented by destinationIndexPath.
So I guess my question becomes: Is there a function to either edit the index Path of the object I insert, or to add an object at a specific index path?

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