Fetch object by property in Core Data

Question

In my iPhone project, I want to write a function that checks wether there\'s an object in my Core Data ManagedObjectContext with a given value for a certain property, say

Answer 1

It's better if you don't do multiple fetching if you want to check for certain properties on the local data. Just do one fetch request using a pre-populated array and then iterate or filter the results.

This is a code snippet from Core Data Programming Guide "Implementing Find-or-Create Efficiently":

// get the names to parse in sorted order
NSArray *employeeIDs = [[listOfIDsAsString componentsSeparatedByString:@"\n"]
        sortedArrayUsingSelector: @selector(compare:)];

// create the fetch request to get all Employees matching the IDs
NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init] autorelease];
[fetchRequest setEntity:
        [NSEntityDescription entityForName:@"Employee" inManagedObjectContext:aMOC]];
[fetchRequest setPredicate: [NSPredicate predicateWithFormat: @"(employeeID IN %@)", employeeIDs]];

// make sure the results are sorted as well
[fetchRequest setSortDescriptors: [NSArray arrayWithObject:
        [[[NSSortDescriptor alloc] initWithKey: @"employeeID"
                ascending:YES] autorelease]]];
// Execute the fetch
NSError *error;
NSArray *employeesMatchingNames = [aMOC
        executeFetchRequest:fetchRequest error:&error];