CODEWITHSUNDEEP
iosswiftcore-data
smyrgl
smyrgl

Reputation: 854

NSFetchedResultsController section grouping by relation

So I have a Core Data entity which I am trying to display in a table view using an NSFetchedResultsController. The relevant model attributes looks something like this:

Post

The relations form a tree with the root Post being the one where parentPost = nil. The way I want this to display is that every root post is the first item in a section and then the rest of the rows are a flattened list of the children of the root.

This is easy enough to arrange manually by doing a fetch request like this:

        let fetchRequest = NSFetchRequest(entityName: Post.entityName())
        fetchRequest.predicate = NSPredicate(format: "parentPost = NULL")
        fetchRequest.sortDescriptors = sortOrder.sortDescriptors
        fetchRequest.fetchBatchSize = 20
        fetchRequest.relationshipKeyPathsForPrefetching = ["allChildren"]

Then I can build the section array from each of the results doing something like this:

    let sectionPost = self.fetchedResultsController!.fetchedObjects![section] as! Post
    var sectionArray = NSMutableArray(object: sectionPost)
    var filteredSet = sectionPost.allChildren.filteredOrderedSetUsingPredicate(NSPredicate(format: "approved != FALSE AND postDeleted != TRUE AND spam != TRUE"))
    sectionArray.addObjectsFromArray(filteredSet.array)

The question is: is there a way to do this all within the FRC? Maintaining a separate datasource from the FRC is complicated and I'd rather find a way to do this with a single fetch request but I don't see a great way of handling this.

Upvotes: 1

Views: 306

Answers (1)

Daij-Djan
Daij-Djan

Reputation: 50129

no the grouping must happen on a key on the entity. so use a transient property or a fetched property to get the relation and make it a key

in your case.. e.g. make all POST objects have a key 'postToGroupBy' or 'postNameToGroupBy or whatever so the post and all its children are in the same group

Upvotes: 1

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