Question

I am using core data first time in my application for my problem I have done google a lot but I didn’t find specific solution.

I have Entity:SubCategory

Attributes:mainCategoryId,subCategoryName.

Now I want to fetch the data like

Select subCategoryName from SubCategory where mainCategoryId=1;

The code which I have implemented is as follows:

 NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"SubCategory" inManagedObjectContext:managedObjectContext];

    [request setEntity:entity];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SubCategoryName == %@",@"Triangular1"];
    [request setPredicate:predicate];

    NSError *error;
    arrSubCategory = [managedObjectContext executeFetchRequest:request error:&error];

How can I fetch similar kind of data in coredata

share your ideas

thanx in advance.

Answer 1

From your question what you need is,

[NSPredicate predicateWithFormat:@"mainCategoryId = %@",@"1"];

So your code will look like,

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
    entityForName:@"SubCategory" inManagedObjectContext:context];
[fetchRequest setEntity:entity];

NSPredicate *predicate =[NSPredicate predicateWithFormat:@"mainCategoryId = %@",@"1"];
[request setPredicate:predicate];

NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
for (NSManagedObject *info in fetchedObjects) {
    NSLog(@"subCategoryName: %@", [info valueForKey:@"subCategoryName"]);
}

The above is just a sample code. Actual implementation could be different based on your requirement.

A tutorial on coredata is here. Check that out as well.