Programmatically update duplicate values in coredata? - ios

Question

I am new in Core Data. I want to update duplicate values. For example my table looks like this
id | Name
============
1 | Joseph
2 | Fernandez
3 | Joseph
4 | James
Say that I want to update Joseph corresponding to id 1 and 4 to "myName". When I tried to update this it only updates the 4th row. I can't find any way to do this in any of the documentation. Can anyone suggest me a solution?
One more question, how can I print all name values?

Answer 1

you will have to read over the documentation to know how to update record
http://www.appcoda.com/core-data-tutorial-update-delete/

Answer 2

James,
I'll try to reply to both your questions with sample code.
To update specific objects you need to se up a new NSFetchRequest with a predicate, grab the objects (of type NSManagedObject), update the values you are interested in and save the context.
So, for example:
NSFetchRequest* fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"YourEntityName"];
// set the predicate (it's equal to set a WHERE SQL clause) filtering on the name for example
// use camel case notation if possible, so instead of Name use name (for this you have to changes your model, if you don't want to do it use Name)
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:#"name == %#", #"Joseph"]];
NSError* error = nil;
NSArray* results = [context executeFetchRequest:fetchRequest error:&error];
// do some error checking here...
for (NSManagedObject resultItem in results) {
// use KVC (for example) to access your object properties
[resultItem setValue:#"myName" forKey:#"name"];
}
// save your context here
// if you don't save, changes are not stored
To print you need to se up a new NSFetchRequest, grab the objects (of type NSManagedObject) and use NSLog.
So for example:
NSFetchRequest* fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"YourEntityName"];
NSError* error = nil;
NSArray* results = [context executeFetchRequest:fetchRequest error:&error];
// do some error checking here...
for (NSManagedObject resultItem in results) {
NSLog(#"%#", [resultItem valueForKey:#"name"]);
}
P.S. The code I provided is quite simple and the predicate I used to specific values check against the name. Since this could be error prone, I would modify the model and using a sort of guid for each objects you need to use (I don't know if id is for that but I would change its name to another one, for example userId). Once done you can check against it.
Hope that helps.

Answer 3

It's as simple as retrieving the NSManagedObject and changing the Name property. You can retrieve the NSManagedObject with a fetch request. Once you changed the property and you want to keep it changed even when you close the application you'll have to do a save on the managedObjectContext.
You'll have to read over the documentation to get up to speed on core data:
http://developer.apple.com/library/mac/#documentation/cocoa/Conceptual/CoreData/Articles/cdBasics.html#//apple_ref/doc/uid/TP40001650-TP1
Edit: just NSLog whatever you want to know, for example log you fetch request results.