CODEWITHSUNDEEP
iosobjective-cnspredicate
user3195388
user3195388

Reputation: 129

NSPredicate returning all objects

I'm trying to use the NSPredicate to only get specific objects. The problem is that all the objects are fetched and it should only be specific objects where the condition is correct. 

- (void)fetchDevices {
    // Fetch the devices from persistent data store

    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Songs"];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Songs" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];
    // retrive the objects with a given value for a certain property
    NSPredicate *predicate = [NSPredicate predicateWithFormat: @"selectedRow == %@" , selectedRowNumber];
    devices = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
    [fetchRequest setPredicate:predicate];

}

The selectedRowNumber is an int declared in the .h file.

A look on my Songs entity:

enter image description here

PS. Please comment below if more information is required and i'll provide it.

Upvotes: 2

Views: 620

Answers (4)

santhu
santhu

Reputation: 4792

There is no need of setting Entity using setEntity. 

[fetchRequest setPredicate:predicate]

Just set predicate, it will work.

- (void)fetchDevices {
    // Fetch the devices from persistent data store

    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Songs"];
    // retrive the objects with a given value for a certain property
    NSPredicate *predicate = [NSPredicate predicateWithFormat: @"selectedRow == %@" , selectedRowNumber];
    [fetchRequest setPredicate:predicate];
    devices = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
    [fetchRequest setPredicate:predicate];

}

Upvotes: 0

Ethan Fang
Ethan Fang

Reputation: 1269

there seems to be two problems.

  1. I think you need to put [fetchRequest setPredicate:predicate]; before devices = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];

  2. Also @"selectedRow == %d" seems not right. You may want to change it to @"selectedRow = %d"

  3. And no need to set entity again.

So the code may look like this.

- (void)fetchDevices {
    int selectedRowNumber = 1;
    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Songs"];
    NSPredicate *predicate = [NSPredicate predicateWithFormat: @"selectedRow = %d" , selectedRowNumber];
    [fetchRequest setPredicate:predicate];
    NSArray *devices = [[managedObjectContext executeFetchRequest:fetchRequest error:nil]     mutableCopy];
}

Let me know how it goes :)

Upvotes: 0

Akhilrajtr
Akhilrajtr

Reputation: 5182

Try this,

NSPredicate *predicate = [NSPredicate predicateWithFormat: @"selectedRow = %@" , [NSNumber numberWithInt: selectedRowNumber]];
[fetchRequest setPredicate:predicate];
devices = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];

Upvotes: 0

Martin R
Martin R

Reputation: 540085

You have to assign the predicate before executing the fetch request.

Also, if selectedRowNumber is an int then you have to use the %d format instead of %@.

NSPredicate *predicate = [NSPredicate predicateWithFormat: @"selectedRow == %d" , selectedRowNumber];
[fetchRequest setPredicate:predicate];
devices = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];

Upvotes: 3

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