Question

我的CoreData中的实体名为myentity，属性名为myuniqueid，我想按如下方式运行SQL查询：

Select * from myentity where myuniqueid == 1000

如何在SQL查询中获取指定的匹配行？这样我想过滤myuniqueid为1000的所有行。

我的代码：

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSManagedObjectContext *context = [self managedObjectContext];
    if (context == nil) {}
    else {
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"myentity" inManagedObjectContext:context];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"myuniqueid == 1000"];
    [fetchRequest setPredicate:predicate];

    [fetchRequest setEntity:entity];
    NSArray *items = [context executeFetchRequest:fetchRequest error:nil];
        for (int i=0; i<4; i++) {
            NSManagedObject *mo = [items objectAtIndex:i];  // assuming that array is not empty
            id value = [mo valueForKey:@"myuniqueid"];
            NSLog(@"SENDER: %@",value);
        }

    }

我收到错误：'Unable to generate SQL for predicate (myuniqueid == 1000) (problem on RHS)'

Answer 1

试试这个谓词：

NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"myentity"];
fetchRequest.predicate = [NSPredicate predicateWithFormat:@"myuniqueid == %@", @(1000)];
NSArray *items = [[self managedObjectContext] executeFetchRequest:request error:nil];

核心数据iOS

1 个答案: