在我看来，在应用程序中应该有 UNIQUE truck_id 响应json，像这样

In my opinion there should be a UNIQUE truck_id in the response json, like this

{
    "trucks": [
        {
            "id": "00000001"
            "model": "Scania",
            "year": "2014",
            "country": "Sweden"
        },
        {
            "id": "00000002"
            "model": "DAF",
            "year": "2012",
            "country": "Ireland"
        }
    ]
}

保存 id $ c>到到模型，并且每次从服务器获取响应时，只需检查是否存在具有相同 id 。

Save the id to Truck model and every time you get response from server, just check if there is a model with same id in core data.

对于每个卡车json，首先提出获取请求

For every truck json, make a fetch request first

NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
request.entity = [NSEntityDescription entityForName:@"Truck" inManagedObjectContext:context];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"truckID = %d", truckIDInResponse];
request.predicate = predicate;
NSError *error = nil;
NSArray *objs = [context executeFetchRequest:request error:&error];
if (error) {
    [NSException raise:@"no truck find" format:@"%@", [error localizedDescription]];
}
if (objs.count > 0) {
    // there is a truck with same id exsist. Use update method
}else {
    // there's no truck with same id. Use insert method
}

truckID 是卡车模型的属性。