R – How to access fetched property in Objective-C 2.0 using Core data

core-dataiphoneobjective c

I'm new to IPhone development and I'm currently trying my hand at Core Data. I have a couple of entities that I've defined in my model. In one entity I have a fetched property. When I generate the Objective-C source files from my model, my entity that I defined with the fetched property does not have a property defined for the fetched property. Why? How do I access the fetched property?

More details in response to Tim:

I have an entity named Library and another entity named Book.
Library has a one to many relationship to Book (Book also has an inverse relationship).
Book has a BOOL property called isCheckedOut.
I defined a fetched property on Library called fetchAllCheckedOutBooks. The destination entity is Book and the predicate is isCheckedOut == 1.

Best Answer

Have you tried using valueForKey: and passing in the name of your fetched property? That's how I would expect it to work. I would also expect that it would return an NSSet object, but that's easily verified by doing this:

id results = [myManagedObject valueForKey:@"fetchedPropertyName"];
NSLog(@"%@", [results className]);

Related Solutions

Objective-c – Best way to implement Enums with Core Data

You'll have to create custom accessors if you want to restrict the values to an enum. So, first you'd declare an enum, like so:

typedef enum {
    kPaymentFrequencyOneOff = 0,
    kPaymentFrequencyYearly = 1,
    kPaymentFrequencyMonthly = 2,
    kPaymentFrequencyWeekly = 3
} PaymentFrequency;

Then, declare getters and setters for your property. It's a bad idea to override the existing ones, since the standard accessors expect an NSNumber object rather than a scalar type, and you'll run into trouble if anything in the bindings or KVO systems try and access your value.

- (PaymentFrequency)itemTypeRaw {
    return (PaymentFrequency)[[self itemType] intValue];
}

- (void)setItemTypeRaw:(PaymentFrequency)type {
    [self setItemType:[NSNumber numberWithInt:type]];
}

Finally, you should implement + keyPathsForValuesAffecting<Key> so you get KVO notifications for itemTypeRaw when itemType changes.

+ (NSSet *)keyPathsForValuesAffectingItemTypeRaw {
    return [NSSet setWithObject:@"itemType"];
}

Ios – How to check if a string contains another string in Objective-C

NSString *string = @"hello bla bla";
if ([string rangeOfString:@"bla"].location == NSNotFound) {
  NSLog(@"string does not contain bla");
} else {
  NSLog(@"string contains bla!");
}

The key is noticing that rangeOfString: returns an NSRange struct, and the documentation says that it returns the struct {NSNotFound, 0} if the "haystack" does not contain the "needle".

And if you're on iOS 8 or OS X Yosemite, you can now do: (*NOTE: This WILL crash your app if this code is called on an iOS7 device).

NSString *string = @"hello bla blah";
if ([string containsString:@"bla"]) {
  NSLog(@"string contains bla!");
} else {
  NSLog(@"string does not contain bla");
}

(This is also how it would work in Swift)

👍

Best Answer

Related Solutions

Objective-c – Best way to implement Enums with Core Data

Ios – How to check if a string contains another string in Objective-C

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