Re: My FetchRequest is not aware of changes I made

FROM : William Turner
DATE : Tue Feb 12 22:36:32 2008

Hi Martin,

I don't have a complete answer for you, but I put together a project 
similar to yours and found a few things of interest:
1) It appears to work correctly with Binary and In-Memory store types.
2) Using XML store, I get the behavior you described.
3) Using SQLite store, I get "Unsupported predicate ALL bars.isHappy 
== 1" in the console.

Looking a little deeper with XML store, I added a second fetch:
[request setEntity:[NSEntityDescription entityForName:@"Bar" 
inManagedObjectContext:managedObjectContext]];
[request setPredicate:[NSPredicate predicateWithFormat:@"isHappy = 
YES"]];
NSArray *results2 = [managedObjectContext executeFetchRequest:request 
error:&error];
NSLog(@"Found %d happy Bars.", [results2 count]);

This fetch correctly returned the number of happy Bars, even while 
incorrectly fetching the number of Foos with all bars.isHappy=YES.

I'll let you know if I figure anything else out, but I thought this 
might spark some productive thoughts...

Wil

On Feb 12, 2008, at 3:49 AM, Martin wrote:

> Hi,
>
> Let Foo and Bar be two entities of my Core Data app. There is a one-
> to-many relationship between the two of them, Foo have bars and each 
> Bar has a foo:
> Foo              Bar
> bars <--->> foo
>
> The Bar entity also has a boolean "isHappy" attribute.
>
> Here is what I do:
>
> - (IBAction)test:(id)sender {
>     
>     NSError *error;
>     NSFetchRequest *request = [[[NSFetchRequest alloc] init] 
> autorelease];
>     [request setEntity:[NSEntityDescription entityForName:@"Foo" 
> inManagedObjectContext:managedObjectContext]];
>     [request setPredicate:[NSPredicate predicateWithFormat:@"ALL 
> bars.isHappy = YES"]];
>     
>     NSArray *results = [managedObjectContext 
> executeFetchRequest:request error:&error];
>     NSLog(@"Found %d Foos with very happy Bars.", [results count]);
>     
>     for (NSManagedObject *foo in results)
>         for (NSManagedObject *bar in [foo mutableSetValueForKey:@"bars"])
>             [bar setValue:[NSNumber numberWithBool:NO] forKey:@"isHappy"];
> }
>
> Let's say that there are 3 Foos when my app launches, each of this 
> Foos have happy bars.
>
> When test: is first called, the log says:
> "Found 3 Foos with very happy Bars."
> Then all the isHappy attributes are changed to NO, which is 
> instantly visually verified in the GUI (the checkboxes get unchecked).
>
> But if I call test: again, the log says:
> "Found 3 Foos with very happy Bars."
>
> Why doesn't the fetch request finds 0 Foos? Why isn't the fetch 
> request aware of the changes just made when the GUI is?
> The only thing that makes it work is to save the context after doing 
> the changes, but I don't want to save at that point.
>
> This behaviour seems to go completely against the documentation: "If 
> an object in a context has been modified, a predicate is evaluated 
> against its modified state, not against the current state in the 
> persistent store."
>
> Thanks,
> Martin.
>
>
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