NSFetchRequest not fetching chat messages in proper order - iphone

Question

I am implementing a chat database using core data in iphone. I have created two entity chatuser and chatmessage. and there is one to many relationship between chatuser and chatmessgae entity. For one chatuser there can be many chatmessages. I am storing data like
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Chatuser"
inManagedObjectContext:self.managedObjectContext];
[request setEntity:entity];
NSPredicate *pred = [NSPredicate predicateWithFormat:#"chatuser == %#", chatuser];
[request setPredicate:pred];
NSArray *userArray=[self.managedObjectContext executeFetchRequest:request error:&error];
if ([userArray count] > 0){
Chatuser *user = [userArray objectAtIndex:0];
Chatmessage *message = [NSEntityDescription insertNewObjectForEntityForName:#"Chatmessage" inManagedObjectContext:self.managedObjectContext];
message.chatmessage = chatmessage;
[user addAllchatmessagesObject:message];
NSError *error;
if(![self.managedObjectContext save:&error])
{
NSLog(#"whoops, couldn't save: %#", [error localizedDescription]);
}
}
// }
else
{
Chatuser *user = [NSEntityDescription insertNewObjectForEntityForName:#"Chatuser" inManagedObjectContext:self.managedObjectContext];
user.chatuser = chatUser;
Chatmessage *message = [NSEntityDescription insertNewObjectForEntityForName:#"Chatmessage" inManagedObjectContext:self.managedObjectContext];
message.chatmessage = chatmessage;
[user addAllchatmessagesObject:message];
NSError *error;
if(![self.managedObjectContext save:&error])
{
NSLog(#"whoops, couldn't save: %#", [error localizedDescription]);
}
}
and fetching data this way
managedObjectContext = appDelegate.managedObjectContext;
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:#"Chatuser" inManagedObjectContext:self.managedObjectContext];
[request setEntity:entity];
NSError *error;
NSPredicate *pred = [NSPredicate predicateWithFormat:#"chatuser == %#", appDelegate.chatUser];
[request setPredicate:pred];
NSArray *userinfo = [self.managedObjectContext executeFetchRequest:request error:&error];
if([userinfo count]>0)
{
Chatuser *user = [userinfo objectAtIndex:0];
NSSet *messageset = user.allchatmessages;
self.messageinfo = [messageset allObjects];
int message_count=[self.messageinfo count];
NSLog(#"Message count : %d", message_count);
for(int i=(message_count-1);i>=0;i--)
{
Chatmessage *chatmsgnew = [self.messageinfo objectAtIndex:i];
[tableArray addObject:chatmsgnew.chatmessage];
}
}
now the problem is that chat messages is not coming in the order in which i am storing them. Like i am storing messages 1,2,3,4. and while fetching its coming like 2,1,4,3.....
I am not getting the problem. Can anybody suggest anything.

Answer 1

A fetch request does not necessarily return the objects in the order they were inserted into the database. If you need a specific order, you have to add an Integer attribute (e.g. messageId) to the entity, and add a sort descriptor to the fetch request:
NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:#"messageId"
ascending:YES];
[request setSortDescriptors:#[sort]];
Added: The above method works if you fetch Chatmessage objects. So instead of fetching a Chatuser first, you could create a fetch request for the Chatmessage entity, with a predicate like
[NSPredicate predicateWithFormat:#"user.chatuser == %#", appDelegate.chatUser]
(assuming that "user" is the inverse relationship from Chatmessage to Chatuser), and the above sort descriptor.
Alternatively, if you have a Chatuser object, then you can sort user.allchatmessages like this:
NSSet *messageset = user.allchatmessages;
NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:#"messageId"
ascending:YES];
self.messageinfo = [[messageset allObjects] sortedArrayUsingDescriptors:#[sort]];