CoreData字符串搜索

[wzckr]

我的数据库里有个字段是name,里面的记录有一条是AA1
我现在想把他找出来，代码是这样写的

+(NSManagedObject *)GetObjectFrom:(NSString *) tablename ForFieldName:(NSString *)fieldname ForValue:(NSString *) value{

AppDelegate *appDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext;

NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entityDescription = [NSEntityDescription
entityForName:tablename
inManagedObjectContext:managedObjectContext];
[request setEntity:entityDescription];
NSPredicate *pred = [NSPredicate
predicateWithFormat:@"(%@=%@)", fieldname,value];
[request setPredicate:pred];
NSError *error;
NSArray *objects = [managedObjectContext executeFetchRequest:request
error:&error];
[request release];
if ([objects count] > 0){
return [objects objectAtIndex:0];
}
else
return nil;

}

我还试了
NSPredicate *pred = [NSPredicate
predicateWithFormat:@"(%@='%@')", fieldname,value];
或
NSPredicate *pred = [NSPredicate
predicateWithFormat:@"(%@==%@)", fieldname,value];
NSPredicate *pred = [NSPredicate
predicateWithFormat:@"(%@=='%@')", fieldname,value];

好象都不行，要怎么写才可以