Core Data combined Query

Question

Hey, i have question related to CoreData. My iphone project has 2 Entities, Organisation and Brand with a 1 to many "BrandsToOrg" relationship and inverse.

So my project has a Mapview, where you can see all the Organisations and a little subview when you click on those Organisations.At the subview there is a "show Brands" Button, which should init a new TableView who only shows the brands belong to the seleceted organisation. Any ideas how i can code that?

thx

NSPredicate *predicate = [NSPredicate predicateWithFormat: @"(TitleMedium == %@)",@"Rock Antenne"];????
NSFetchRequest *request = [[NSFetchRequest alloc] init];
  NSEntityDescription *entity = [NSEntityDescription entityForName:self.entityName inManagedObjectContext:managedObjectContext];
  [request setEntity:entity]; 


  if(predicate != nil)
  {
   [request setPredicate:predicate];
  }

  // If a sort key was passed, use it for sorting.
  NSString *sortKey=@"TitleMedium";
  BOOL sortAscending=YES;
  if(sortKey != nil)
  {
   NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:sortKey ascending:sortAscending];
   NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
   [request setSortDescriptors:sortDescriptors];
   [sortDescriptors release];
   [sortDescriptor release];
  }

  NSError *error;

  NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];

  [request release];
  [self setEntityArray:mutableFetchResults];

Answer 1

Here's an example of how you would do this with a top-level UITableView of orgs and a detailed table view of brands. At the top level, you do a fetch request for the orgs and display them. When a particular one is selected, you create the detail view of brands. The BrandsViewController object has a "org" property that tells is what to display; it can then refer to "org.brands" (which is the Core Data one-to-many relationship) to locate all the brands for that display. Note that you don't need to do an explicit Core Data fetch within the BrandsViewController to get the brands.

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

BrandsViewController *targetViewController = [[BrandsViewController alloc]
    initWithNibName:@"BrandsView" bundle:nil];
    // pass managedObjectContext along to new view controller
targetViewController.managedObjectContext = self.managedObjectContext;

// Pass the selected org to the new view controller
targetViewController.org = (Organisation *)[fetchedResultsController objectAtIndexPath:indexPath];

[[self navigationController] pushViewController:targetViewController animated:YES];
[targetViewController release];
}