Sort NSPredicate with in clausule with array's order

问题

I have a NSPredicatethat does a search of id within an NSArrayof ids, something like

('id in %@',array)

Is there a way to get the resultset of that fetch sorted with the same array's order?

The code I have now is

+(NSArray*)     findIn:(NSArray*)identifiers{

    if(identifiers == nil) return nil;

    NSPredicate *searchFilter   = [NSPredicate predicateWithFormat:@"id IN %@", identifiers];
    NSArray     *fetchedObjects =  [GSBaseModel setupFetch:[[self class] managedObjectEntityName] andFilter:searchFilter andSortKey:nil];

    if([fetchedObjects count] == 0){
        return nil;
    }
    return fetchedObjects;
}

The setupfecth just does the following:

NSFetchRequest      *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity   = [NSEntityDescription entityForName:entityName inManagedObjectContext:[NSManagedObjectContext MR_defaultContext]];
[fetchRequest setEntity:entity];
return  = [[NSManagedObjectContext MR_defaultContext] executeFetchRequest:fetchRequest error:&error];

回答1:

I finally soved it this way

Thanks to Sort NSArray of custom objects based on sorting of another NSArray of strings

+(NSArray*)sortWithArray:(NSArray*)toSort sorted:(NSArray*)sortedIdentifiers{
    NSMutableArray *sorted = [NSMutableArray array];

    // pre-populate with objects
    for (int i = 0; i < sortedIdentifiers.count; i++)
    {
        [sorted addObject:[NSNull null]];
    }
    // place the items at the correct position
    for (NSManagedObject *a in toSort)
    {
        NSNumber* identifier = [a valueForKey:@"id"];
        NSUInteger idx = [sortedIdentifiers indexOfObject:[identifier stringValue]];
        if (idx != NSNotFound)
        {
            [sorted setObject:a atIndexedSubscript:idx];
        }
    }
    // finally remove all the unecesarry placeholders if one array was smaller
    [sorted removeObject:[NSNull null]];
    return sorted;
}

回答2:

If you want to fetch core data objects and link them up with an array of id's you should consider using the ever so powerful NSDictionary:

So once you have fetched all your objects simply store those objects in a dictionary keyed by id:

NSDictionary *managedObjectsKeyedByID = [NSDictionary dictionaryWithObjects:fetchedObjects forKeys:[fetchedObjects valueForKey:@"identifier"]];

Now you can iterate over your array and check for matches using your dictionary:

for (NSString *identifier in arrayOfServerIDs) {
    NSManagedObject *existingObject = managedObjectsKeyedByID[identifier];
    if(!existingObject) {
       //insert a new one
    } else {
       //update
    }
}

来源：https://stackoverflow.com/questions/26989573/sort-nspredicate-with-in-clausule-with-arrays-order

标签

objective-c

core-data

nspredicate