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Basic Using of CoreData

Based on Xcode 7.2(7C68)

SETUP COREDATA

1. Add an entity to the .xcdatamodeld then attributes to the entity. When finish the entity and attributes, create NSManagedObject subclass from the “Editor” menu.
2. Declare a static managedObjectContext variable in the top of AppDelegate.swift to use conveniently in the future:
   let managedContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext

WRITING

1. Get the entity out from ManagedContext: let entity = NSEntityDescription.entityForName("Entity", inManagedObjectContext: managedContext)

2. Decalre a new record:

//  "Entity" in the next line is the name of NSManagedObject subclass<br></br>
let newdiary = Entity(entity: entity!, insertIntoManagedObjectContext:managedContext)

3. Edit the attributes value of the new record:

newdiary.day = Int(day.text!)<br></br>
newdiary.des = "This is Description."<br></br>
newdiary.fav = true<br></br>
newdiary.id = 20160117<br></br>
newdiary.img = nil // Here supposed to be a Date variable.<br></br>
newdiary.month = 1<br></br>
newdiary.year = 2016

4. Save the new record to CoreData:

do {<br></br>
try managedContext.save()<br></br>
} catch {<br></br>
fatalError("Failure to save context: \(error)")<br></br>
}

READ

1. Declare two NSFetchResultsController inside the ViewController class:

var fetchedDay : NSFetchedResultsController!<br></br>
var fetchedDes : NSFetchedResultsController!

2. Create a fetch request (target entity is “Entity”): let fetchRequest = NSFetchRequest(entityName:"Entity")

3. Sort the fetch result (ascending by the column “day”): fetchRequest.sortDescriptors = [NSSortDescriptor(key: "day", ascending: true)]

4. Init two NSFetchResultsController:

fetchedDay = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managedContext,sectionNameKeyPath: "day", cacheName: nil)<br></br>
fetchedDes = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managedContext,sectionNameKeyPath: "des", cacheName: nil)

5. Try to fetch data:

try self.fetchedDay.performFetch()
try self.fetchedDes.performFetch()

6. Do not forget to handle errors thrown from try command (embed all the reading codes inside do{} and catch error):

do {
......
} catch {
fatalError("Failure to save context: \(error)")
}

7. Get data out of fetch result (get the Xth data content):

var day = fetchedDay.sections![X].name<br></br>
var des = fetchedDes.sections![X].name

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