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iosperformancecocoa-touchindexingnsfetchedresultscontroller
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Reputation: 2994

NSFetchedResultsController performance with UITableView index

I'm learning about NSFetchedResultsController and one thing puzzles me. The NSFetchedResultsController is used in combination with UITableView to help with fetching performance and to calculate which records to fetch based on what is currently shown in the UITableView.

When you use a UITableView index (like the first letters in the Addressbook app) doesn't that mean the whole dataset will be loaded to determine all the first letters of all the sections?

Doesn't the use of the index prevent the NSFetchedResultsController from being smart about what it loads?

Upvotes: 0

Views: 246

Answers (1)

Carl Veazey
Carl Veazey

Reputation: 18363

NSFetchedResultsController builds its index from the sectionKeyPath. One would assume that to get the values for this, a fetch would be performed to only get unique values for this key and not anything close to the full data set. For example, it could be doing something like making an NSFetchRequest with a result type of NSDictionaryResultType, returnsDistinctResults set to YES, and propertiesToFetch set only to sectionKeyPath.

Upvotes: 1

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