CODEWITHSUNDEEP
iosiphoneobjective-ccore-datansfetchedresultscontroller
Eyal
Eyal

Reputation: 10818

Core Data - query to-many relationship

I have a core data model that look something like this: 

Author
======
- name
- bio

- books (to-many relationship)


Book
====
- title
- release date

- author (to-one relationship)

I present to the user a table view of authors each table cell represent an author and shows his name and the title of the latest book he wrote.

To show the list of authors I use a NSFetchedResultsController with the following NSFetchRequest : 

NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Author"];
request.predicate = nil;
request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES]];
request.fetchBatchSize = 20;

My question is:

How should I get the title of the latest book for each author? can I get that info in my original request or do I need to do some additional requests?

Upvotes: 1

Views: 103

Answers (2)

bilobatum
bilobatum

Reputation: 8918

You don't need to execute another fetch request if you already have an Author managed object. Just create a sorted array from the Author's books property. To accomplish this, you could use NSSet's sortedArrayUsingDescriptors: method and pass in a descriptor that sorts by release date.

Upvotes: 1

Duncan Groenewald
Duncan Groenewald

Reputation: 8988

To get it as part of the same request you could include an attribute on the Author object that stores the latest book

Author
======
- name
- bio
- latestBook

- books (to-many relationship)

Then to get the details simply use author.latestBook.title

You would also need to set the latestBook attribute when you add the latest book to the books attribute.

Alternately it could be a transient attribute that you calculate from the set of books based on the latest releaseDate.

Upvotes: 0

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