Question

我在DB中有一些消息，每次都会从该用户的服务器获得总消息。我必须比较两个数组并需要过滤新消息。每条消息都有一个唯一的ID，即。，messageId

NSMutableArray *arrayMessagesServer = [response objectForKey:@"messageList"];
    arrayMessagesDB=[[NSMutableArray alloc]initWithArray:[self getMessagesFromDB]];



    for (int i = 0; i<[arrayMessagesServer count]; i++)
    {

        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"messageId == %i", [[arrayMessagesServer objectAtIndex:i] integerValue]];


        //If message not exists, saving message to DB
        if(![arrayMessagesDB filteredArrayUsingPredicate:predicate])
        {
            NSDictionary *dict = [arrayForMessagesInServer objectAtIndex:i];

            Messages *objMessages = [NSEntityDescription insertNewObjectForEntityForName:@"Messages" inManagedObjectContext:context];
            [objMessages setValue:[dict objectForKey:@"message"] forKey:@"messageBody"];
            [objMessages setValue:[dict objectForKey:@"messageId"] forKey:@"messageId"];
            [objMessages setValue:[NSString stringWithFormat:@"%@",[dict objectForKey:@"messageType"]] forKey:@"messageType"];
        }

    }

    NSError *error1;
    if (![context save:&error1])
    {
        NSLog(@"Problem saving: %@", [error1 localizedDescription]);
    }

Answer 1

如果我理解正确，您需要将消息列表与服务器同步，并仅向数据库插入新消息，但尚未在数据库中显示。

您可以使用IN语句。如下所示：

NSMutableArray *arrayMessagesServer = [response objectForKey:@"messageList"];
arrayMessagesDB = [[NSMutableArray alloc]initWithArray:[self getMessagesFromDB]];

// this gives you an array of identifiers (NSString? as in your model): 
NSArray *existingIdentifiers = [arrayMessagesDB valueForKey:@"messageId"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"messageId NOT IN %@", existingIdentifiers];
NSArray *newMessages = [arrayMessagesServer filteredArrayUsingPredicate:predicate];

快速而简单！

如何使用NSPredicate从另一个NSMutableArray中过滤NSMutableArray

1 个答案: