核心数据setReturnsDistinctResult不工作

Question

所以我正在构建一个小应用程序,它使用大约25mb大小的核心数据库和4个实体.这是公交车时刻表.

在一个名为"停止"的表中,有大约1300个公共汽车站的条目,其中包含"名称","id","经度","纬度"和夫妻关系.现在有许多具有相同名称属性但坐标和ID不同的站点.所以我想在表视图中显示所有不同的停止名称,我正在使用带有NSDictionaryResultType和setPropertiesToFetch的setReturnsDistinctResults.但是setReturnsDistinctResult不起作用,我仍然得到所有条目.

继承人代码:

- (NSFetchRequest *)fetchRequest {
    if (fetchRequest == nil) {
        fetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity =  [NSEntityDescription entityForName:@"Stop" inManagedObjectContext:managedObjectContext];
        [fetchRequest setEntity:entity];
        NSArray *sortDescriptors = [NSArray arrayWithObject:[[[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES] autorelease]];
        [fetchRequest setSortDescriptors:sortDescriptors];
        [fetchRequest setResultType:NSDictionaryResultType];
        [fetchRequest setPropertiesToFetch:[NSArray arrayWithObject:[[entity propertiesByName] objectForKey:@"name"]]];
        [fetchRequest setReturnsDistinctResults:YES];
        DebugLog(@"fetchRequest initialized");
    }
    return fetchRequest;
}

/////////////////////

- (NSFetchedResultsController *)fetchedResultsController {
    if (self.predicateString != nil) {
        self.predicate = [NSPredicate predicateWithFormat:@"name CONTAINS[cd] %@", self.predicateString];
        [self.fetchRequest setPredicate:predicate];
    } else {
        self.predicate = nil;
        [self.fetchRequest setPredicate:predicate];
    }
    fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:self.fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:sectionNameKeyPath cacheName:nil];

    return fetchedResultsController;
}  

//////////////

- (UITableViewCell *)tableView:(UITableView *)table cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }

    cell.textLabel.text = [[fetchedResultsController objectAtIndexPath:indexPath] valueForKey:@"name"];

    return cell;
}

Answer 1

这对你来说可能会迟到,但可能对其他人有帮助.

我有同样的问题.我发现,如果持久存储类型是NSSQLiteStoreType,则returnDistinctResults有效.但是对于NSXMLStoreType,不同的值不起作用.

我没有测试过NSBinaryStoreType和NSInMemoryStoreType的结果.