CODEWITHSUNDEEP
iosobjective-ccore-data
Prez
Prez

Reputation: 227

Fetching entity attributes directly from coredata entity

I have an Entity called Devices in CoreData. Devices have following attributes: Name, model, manufacturer, owner. All attributes are of string type. I am using the following code to fetch values from Entity devices using predicate

 NSEntityDescription *entity = [NSEntityDescription entityForName:@"Devices" inManagedObjectContext:self.managedObjectContext];

NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];

request.fetchLimit = Device_LIMIT;
NSSortDescriptor *sortDisc = [NSSortDescriptor sortDescriptorWithKey:@"model" ascending:YES];
[request setSortDescriptors:@[sortDisc]];
NSError *error;
NSArray *array = [self.managedObjectContext executeFetchRequest:request error:&error];   
if (array) {

    arrName = [array valueForKey:@"Name"];
}

return arrName;

I am getting the desired result this way.But, my question is how can I directly fetch an array from Device Entity for Name attribute, without adding any if-else or for in condition.

Upvotes: 0

Views: 899

Answers (4)

Tom Harrington
Tom Harrington

Reputation: 70976

You need to fetch an array from Core Data to get these values-- that's just how Core Data works. You could change your code to use NSDictionaryResultType, but then you'd just get an array of dictionaries instead of an array of managed objects. What you're doing is correct, an there's no short cut to get name values without getting an array and extracting the names from that array.

Upvotes: 0

taitanxiami
taitanxiami

Reputation: 119

The return value for the method executeFetchRequest is an objects array, so you must use a for-loop to take the name attribute out.

Upvotes: 0

George Brown
George Brown

Reputation: 1144

A nil array is only returned if the fetch request failed with an error.

Your code should be structured such that if there is no array, you should deal with the error.

EDIT: This is fairly true for most methods that return something and take an error as an argument in cocoa. Usually if nothing is returned, then the error should be checked.

Upvotes: 0

Imad Ali
Imad Ali

Reputation: 3301

Do a for-loop to add values to arrName as:

NSMutableArray *arrName = [NSMutableArray new];

for (NSManagedObject *object in array) {
    [arrName addObject:object[@"Name"]];
}

Upvotes: 0

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