Core Data - Simple Query Question

Question

Howdy all,

I am working on a simple Core Data app. I have two classes: Client and Home. There is a one-to-many relationship between Clients and Homes (i.e., a Client can have many Homes. Among other attributes, the Home class has one called purchaseDate.

I am trying to write two methods on the Client class: -homesByDate and -firstHome. -homesByDate should return either an NSArray or NSSet of the client's homes sorted by purchaseDate. -firstHome should return just the first home that the client purchased.

I know that given a Client, I can use self.homes to access all of the client's homes, but how do I implement the methods above? Does this involve applying some sort of an NSPredicate?

Help! Thanks!

Answer 1

You seek NSSortDescriptor!

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"purchaseDate" ascending:YES];
//Obtain arrayOfHomes however you'd like
homesByDate = [arrayOfHomes sortedArrayUsingSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
firstHome = [homesByDate objectAtIndex:0];

I should also point out that it's common to let NSArrayController do the sorting for you (if, for example, homesByDate is just for display in a table view or something). You can use setSortDescriptors or use bindings. (This is also handy if you want the user to be able to choose from several orders.)