Hi,
I am building a core data iphone app, and having trouble with retrieving one-many relationship data. Please bear with me while I explain.
I have used the data model designer to setup an entity called "Item" that contains many entities called "Comment". I then retrieve multiple entities and display them in a UITableView
. I fetch these entities like this (in the viewDidLoad
method):
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Items" inManagedObjectContext:self.managedObjectContext];
[request setEntity:entity];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(Item_to_Areas.Name LIKE %@)",[areaManagedObject valueForKey:@"Name"]];
[request setPredicate:predicate];
[request setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObject:@"Item_to_item_comments"]];
NSLog(@"Results: %@", [mutableItemsFetchResults description]);
mutableItemsFetchResults = [[managedObjectContext executeFetchRequest:request error:nil] mutableCopy];
[request release];
When the user taps on a row, I select the particular entiny, pass it to a new table view controller in its init method, and push the new view controller to the stack:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
NSLog(@"itemObject: %@", [mutableItemsFetchResults objectAtIndex:indexPath.row]);
InspectionItemCommentsViewController *itemCommentsViewController = [[InspectionItemCommentsViewController alloc]
initWithManagedObjectContext:self.managedObjectContext
itemObject:[mutableItemsFetchResults objectAtIndex:indexPath.row]];
itemCommentsViewController.hidesBottomBarWhenPushed = YES;
[self.navigationController pushViewController:itemCommentsViewController animated:YES];
[itemCommentsViewController release];
}
In the first block the NSLog output shows that the "Item_to_item_comments" relationship entities were retrieved, but in the second, that it wasn't even though I invoked [request setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObject:@"Item_to_item_comments"]].
Here is part of the first NSLog output:
Results: (
"<NSManagedObject: 0xb356b70> (entity: Items; id: 0xb34fe60 <x-coredata://E43A90B5-AF0E- 4394-B4A7-5EFE74E181F8/Items/p1> ; data: {\n Clean = nil;\n Description = \"\";\n ItemToInformation = \"<relationship fault: 0x5e1ef00 'ItemToInformation'>\";\n \"Item_to_Areas\" = \"0xb33fd30 <x-coredata://E43A90B5-AF0E-4394-B4A7-5EFE74E181F8/Areas/p1>\";\n \"Item_to_item_comments\" = \"<relationship fault: 0x5e1d300 'Item_to_item_comments'>\";\n Keys = nil;\n Name = Other;\n \"Tenant_agrees\" = nil;\n Undamaged = nil;\n Working = nil;\n})",
"<NSManagedObject: 0xb35a930> (entity: Items; id: 0xb32acc0 <x-coredata://E43A90B5-AF0E-4394-B4A7-5EFE74E181F8/Items/p2> ; data: {\n Clean = nil;\n Description = \"\";\n ItemToInformation = \"<relationship fault: 0x790de40 'ItemToInformation'>\";\n \"Item_to_Areas\" = \"0xb33fd30 <x-coredata://E43A90B5-AF0E-4394-B4A7-5EFE74E181F8/Areas/p1>\";\n \"Item_to_item_comments\" = (\n \"0xb35bcb0 <x-coredata://E43A90B5-AF0E-4394-B4A7-5EFE74E181F8/Item_Comments/p13>\",\n \"0xb35bcd0 <x-coredata://E43A90B5-AF0E-4394-B4A7-5EFE74E181F8/Item_Comments/p37>\",\n \"0xb35bca0 <x-coredata://E43A90B5-AF0E-4394-B4A7-5EFE74E181F8/Item_Comments/p5>\",\n \"0xb35bcc0 <x-coredata://E43A90B5-AF0E-4394-B4A7-5EFE74E181F8/Item_Comments/p26>\"\n );\n Keys = nil;\n Name = Lights;\n \"Tenant_agrees\" = nil;\n Undamaged = nil;\n Working = nil;\n})",
You can see that the Items entities are fetched, including Item_to_item_comments
. Here's the second NSLog:
itemObject: <NSManagedObject: 0xe20af50> (entity: Items; id: 0xe209fc0 <x- coredata://E43A90B5-AF0E-4394-B4A7-5EFE74E181F8/Items/p2> ; data: {
Clean = nil;
Description = "";
ItemToInformation = "<relationship fault: 0xe302e40 'ItemToInformation'>";
"Item_to_Areas" = "0xe500b90 <x-coredata://E43A90B5-AF0E-4394-B4A7-5EFE74E181F8/Areas/p1>";
"Item_to_item_comments" = "<relationship fault: 0xe302e60 'Item_to_item_comments'>";
Keys = nil;
Name = Lights;
"Tenant_agrees" = nil;
Undamaged = nil;
Working = nil;
})
Now, Item_to_item_comments
is fault. Similarly, in the pushed view controller, the Items entity is passed, but Item_to_item_comments
is not.
I think I am missing something obvious, but after a day spend on this problem, I can't figure it out.
Any help would be appreciated.
Peter