我有2个实体使用NSStrings作为唯一属性.

创建比较NSStrings的谓词的正确方法是什么？

目前我有：
[NSPredicate predicateWithFormat：@“unique =％@”,uniqueValue];

我有一种感觉,这比较指针地址,而不是实际的字符串值,但我不能确认.我需要返回yes以进行精确的字符串匹配.

-(BOOL)uniqueEntityExistsWithEnityName:(NSString*)entityName UniqueKey:(NSString*) uniqueKey UniqueValue:(NSString*)uniqueValue SortAttribute:(NSString*)sortDescriptorAttribute ManagedObjectContext:(NSManagedObjectContext*) context;
{
    BOOL returnValue = NO;

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:entityName];

//what is the correct predates to compare the text an string core data property against a passed in string?
    request.predicate = [NSPredicate predicateWithFormat:@"unique= %@",uniqueValue];

    NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:sortDescriptorAttribute ascending:YES];
    request.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];   

    NSError *error = nil;
    NSArray *matches = [context executeFetchRequest:request error:&error];
    if (!matches)
    {
         NSLog(@"Error: no object matches");
    }
    else if([matches count] > 1) {
        NSLog(@"Error: More than one object for unique record");
        returnValue = YES;

    } else if ([matches count] == 0) {
        returnValue = NO;
    } else {
        returnValue = YES;
    }

    return returnValue;
}