5

NSPredicateから明確な結果を得ようとしています。

私のコード：

    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Members" inManagedObjectContext:context];
    request.entity = entity;
    request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"city"
                                                                                     ascending:YES
                                                                                      selector:@selector(caseInsensitiveCompare:)]];

    request.predicate = [NSPredicate predicateWithFormat:@"memberDeleted == %@", [NSNumber numberWithBool:NO]];

    NSDictionary *properties = [entity propertiesByName];
    request.propertiesToFetch = [NSArray arrayWithObject:[properties objectForKey:@"city"]];
    request.returnsDistinctResults = YES;

    request.fetchBatchSize = 20;

    NSFetchedResultsController *frc = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                                          managedObjectContext:context
                                                                            sectionNameKeyPath:nil
                                                                                     cacheName:@"CityCache"];
    [request release];

    self.fetchedResultsController = frc;
    [frc release];

問題は、結果が同じ都市を何度も返すことです。このエンティティには多数のメンバーがあり、各メンバーにはプロパティ「city」があります。

私は何が間違っているのですか？

ありがとう、

RL

4

3 に答える 3

7

のをに設定しresultTypeてNSFetchRequestくださいNSDictionaryResultType。デフォルトでは実際のオブジェクトが返されるため、は無視されpropertiesToFetchます。

于 2011-10-08T18:48:15.900 に答える
6

@Alexの助けを借りて、FRCを使用しない最終的なコードを次に示します。

NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Members" inManagedObjectContext:self.managedObjectContext];
request.entity = entity;
request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"city"
                                                                                 ascending:YES
                                                                                  selector:@selector(caseInsensitiveCompare:)]];

request.predicate = [NSPredicate predicateWithFormat:@"memberDeleted == %@", [NSNumber numberWithBool:NO]];

NSDictionary *properties = [entity propertiesByName];
request.propertiesToFetch = [NSArray arrayWithObject:[properties objectForKey:@"city"]];
request.returnsDistinctResults = YES;
request.resultType = NSDictionaryResultType;
request.fetchBatchSize = 20;

NSError *error = nil;
NSArray *tempArray = [self.managedObjectContext executeFetchRequest:request error:&error];

NSMutableArray *cities = [[NSMutableArray alloc] init];
for (int i=0; i < [tempArray count]; i++){
    NSDictionary *tempDict = [NSDictionary dictionary];
    tempDict = [tempArray objectAtIndex:i];

    if ([tempDict objectForKey:@"city"] != nil)
        [cities addObject:[tempDict objectForKey:@"city"]];
}

//if the tempArray has no nil values, it's more efficient with:
//NSArray* cities = [tempArray valueForKeyPath:@"city"];

self.cityArray = cities;
[cities release];
[request release];

これにより、都市のリストを含むNSArrayが返されます。

ありがとう。

于 2011-10-08T20:32:20.940 に答える
3

公式ドキュメントから：

NSManagedObjectContext *context = <#Get the context#>;

NSEntityDescription *entity = [NSEntityDescription  entityForName:@"<#Entity name#>" inManagedObjectContext:context];

NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];
[request setResultType:NSDictionaryResultType];
[request setReturnsDistinctResults:YES];
[request setPropertiesToFetch :[NSArray arrayWithObject:@"<#Attribute name#>"]];

// Execute the fetch.
NSError *error;
id requestedValue = nil;
NSArray *objects = [managedObjectContext executeFetchRequest:request error:&error];
if (objects == nil) {
    // Handle the error.
}
于 2012-06-28T20:19:11.717 に答える