实体属性的访问值

Question

我有一个如下所示的 Core Data 对多关系：

Athlete(evals)<->>Eval(whosEval)

我有一个运动员的表格视图，它显示了数据库中的所有运动员。我想将字幕文本设置为 Eval 属性，假设它被称为“date_recorded”问题是，每个运动员可能有超过 1 个 eval。我需要选择 evalArray 中的最后一个对象，然后显示每个 Athlete 的相关 Eval 属性，因此每个 Athlete 的字幕文本可能会有所不同。我将如何为表格中的每个单元格执行此操作？这是我到目前为止所得到的：

allathletes.m

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Athlete Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    Athlete *athlete = (Athlete *)[athleteArray objectAtIndex:indexPath.row];
    cell.textLabel.text =[athlete full];
    cell.detailTextLabel.text = //eval attribute "date_recorded"

    AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
    _managedObjectContext = [appDelegate managedObjectContext];

    NSFetchRequest *request = [[NSFetchRequest alloc] init];

    NSFetchRequest *athleteRequest = [[NSFetchRequest alloc] init];

    [athleteRequest setEntity:[NSEntityDescription entityForName:@"Athlete" inManagedObjectContext:_managedObjectContext]];
    NSError *athleteError = nil;
    NSPredicate *athletePredicate = [NSPredicate predicateWithFormat:@"full == %@", athlete.full];
    [athleteRequest setPredicate:athletePredicate];
    NSArray *results = [_managedObjectContext executeFetchRequest:athleteRequest error:&athleteError];
    Athlete *currentAthlete = [results objectAtIndex:0];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"whosEval == %@", currentAthlete];
    [request setPredicate:predicate];
    NSEntityDescription *eval = [NSEntityDescription entityForName:@"Eval" inManagedObjectContext:_managedObjectContext];
    [request setEntity:eval];



    NSSortDescriptor *sortDescriptor =
    [[NSSortDescriptor alloc] initWithKey:@"date_recorded"
                                ascending:NO
                                 selector:@selector(localizedCaseInsensitiveCompare:)];
    NSArray *sortDescriptors = [[NSArray alloc]initWithObjects:sortDescriptor, nil];
    [request setSortDescriptors:sortDescriptors];

    NSError *error = nil;
    NSMutableArray *mutableFetchResults = [[_managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
    if (mutableFetchResults == nil){
        //handle error
    }

    NSMutableArray *lastEvalArray = mutableFetchResults;

Eval *lastEval = lastEvalArray.lastObject;

cell.detailTextLabel.text = lastEval.date_recorded;

    return cell;
}

Answer 1

如果date_recorded 是NSDate 属性，那么您可以这样做

Athlete *athlete = (Athlete *)[athleteArray objectAtIndex:indexPath.row];
NSDate *lastRecorded = [athlete valueForKeyPath:@"@max.evals.date_recorded"];

然后使用NSDateFormatter 将lastRecorded 转换为NSString 和 将其分配给cell.detailTextLabel.text。