核心数据集ReturnsDistinctResult 不起作用 [英] Core data setReturnsDistinctResult not working

问题描述

所以我正在构建一个小型应用程序，它使用具有 4 个实体的 ~25mb 大小的核心数据数据库.这是公交车时刻表.

So i'm building a small application, it uses core data database of ~25mb size with 4 entities. It's for bus timetables.

在一个名为Stop"的表中，有大约 1300 个公交车站条目，具有属性name"、id"、longitude"、latitude"和夫妻关系.现在有许多具有相同 name 属性但不同坐标和 id 的站点.所以我想在表视图中显示所有不同的停止名称，我使用 setReturnsDistinctResults 和 NSDictionaryResultType 和 setPropertiesToFetch.但是 setReturnsDistinctResult 不起作用，我仍在获取所有条目.

In one table named "Stop" there are ~1300 entries of bus stops with atributes "name", "id", "longitude", "latitude" and couple relationships. Now there are many stops with identical name attribute but different coordinates and id. So I want to show all distinct stop names in table view, i'm using setReturnsDistinctResults with NSDictionaryResultType and setPropertiesToFetch. But setReturnsDistinctResult is not working and I'm still getting all entries.

这里的代码:

- (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;
}

推荐答案

这对你来说可能有点晚，但可能会帮助其他人.

This may be late for you, but may help others.

我遇到了同样的问题.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.

I had the same problem. What I found is that, if persistant store type is NSSQLiteStoreType the returnDistinctResults works. But for NSXMLStoreType distinct values are not working.

我还没有测试 NSBinaryStoreType 和 NSInMemoryStoreType 的结果.

I haven't tested results for NSBinaryStoreType and NSInMemoryStoreType.

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