iphone sqlite NSDate错误

我在iphone应用程序中使用核心数据，但在某些情况下，我使用sqlite访问数据，并且NSDate出现问题.

i use core data in my iphone app, but in some case i use sqlite to access to data and ia have a problem with NSDate.

NSDate *now = [NSDate date];
        NSCalendar *calender = [NSCalendar currentCalendar];;
        NSDateComponents *comp = [calender components:NSYearCalendarUnit fromDate:now];
        [comp setDay:1];
        [comp setMonth:1];
        NSDate *yearAgo = [calender dateFromComponents:comp];
        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"date > %@",yearAgo];

此代码有效并从年初开始选择记录，但是如果我使用sqlite原始查询

This code works and select records from the start of year, but if i use sqlite raw query

NSDate *current=[NSDate date];
            NSDateComponents *comps = [gregorian components:(NSDayCalendarUnit | NSMonthCalendarUnit |NSYearCalendarUnit) fromDate:current];
            [comps setDay:1];
            [comps setMonth:1];

            NSDate *yearDate = [gregorian dateFromComponents:comps];

            [where appendFormat:@"zdate > '%@' ",yearDate];

我有一个问题，错误的日期由记录决定，在核心日期中具有日期的记录(如2008年1月1日)在sqlite中具有的日期类似于1977年.如何解决?可能是我在查询中使用NSDate错了吗?

I have a problem, wrong date determined by the records, Records that in core date has date like 2008-01-01 in sqlite have dates like 1977 year. How to fix it? May be I was wrong to use NSDate in the query?