CoreData Edit/Overwrite Object

问题

I am playing around with a new project, a split view iPad app using Core Data, and I was wondering, as its fairly clear how to add and remove an item. If I was to say alter this to hold text, then that text be shown in a UITextView, how can I edit or overwrite an object in CoreData?

So the user types their note in the UITextView and when they leave that it edits and saves the note (object in the table view) they have currently selected.

Appreciate any help thanks.

回答1:

You simply request the existing object using an NSFetchRequest, change whatever fields need to be updated (a simple myObject.propertyName setter is all that's required), and then perform a save action on the data context.

EDIT to add code example. I agree with MCannon, Core Data is definitely worth reading up about.

This code assumes you created the project with a template that includes Core Data stuff, such that your app delegate has a managed object context, etc. Note that there is NO error checking here, this is just basic code.

Fetching the object

// Retrieve the context
if (managedObjectContext == nil) {
    managedObjectContext = [(YourAppNameAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
}

// Retrieve the entity from the local store -- much like a table in a database
NSEntityDescription *entity = [NSEntityDescription entityForName:@"YourEntityName" inManagedObjectContext:managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];

// Set the predicate -- much like a WHERE statement in a SQL database
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"YourIdentifyingObjectProperty == %@", yourIdentifyingQualifier];
[request setPredicate:predicate];

// Set the sorting -- mandatory, even if you're fetching a single record/object
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"yourIdentifyingQualifier" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[request setSortDescriptors:sortDescriptors];
[sortDescriptors release]; sortDescriptors = nil;
[sortDescriptor release]; sortDescriptor = nil;

// Request the data -- NOTE, this assumes only one match, that 
// yourIdentifyingQualifier is unique. It just grabs the first object in the array. 
YourEntityName *thisYourEntityName = [[managedObjectContext executeFetchRequest:request error:&error] objectAtIndex:0];
[request release]; request = nil;

Update the object

thisYourEntityName.ExampleNSStringAttributeName = @"The new value";
thisYourEntityName.ExampleNSDateAttributeName = [NSDate date];

Save the change

NSError *error;
[self.managedObjectContext save:&error];

Now your object/row is updated.

回答2:

http://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html will show you how to fetch an entity,

http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdUsingMOs.html will show you how to change properties, and save them.

core data is something where you really want to read a lot of the apple documentation and become familiar, it will save you hours in the long run. hope this helps!

来源：https://stackoverflow.com/questions/4293026/coredata-edit-overwrite-object