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Refetch everything when there are inserted items, performance with trying to merge change was just too bad

This commit is contained in:
Shadowfacts 2022-06-09 23:28:34 -04:00
parent d906ec47f9
commit b79c8af12c
1 changed files with 40 additions and 66 deletions
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106
Reader/Screens/Items/ItemsViewController.swift
View File

@ -75,21 +75,9 @@ class ItemsViewController: UIViewController {
])
fetchRequest.sortDescriptors = [NSSortDescriptor(key: "published", ascending: false)]
do {
let ids = try fervorController.persistentContainer.viewContext.fetch(fetchRequest)
var snapshot = NSDiffableDataSourceSnapshot<Section, NSManagedObjectID>()
snapshot.appendSections([.items])
snapshot.appendItems(ids, toSection: .items)
dataSource.apply(snapshot, animatingDifferences: false)
NotificationCenter.default.addObserver(self, selector: #selector(managedObjectsDidChange), name: .NSManagedObjectContextObjectsDidChange, object: fervorController.persistentContainer.viewContext)
} catch {
let alert = UIAlertController(title: "Error fetching items", message: error.localizedDescription, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
present(alert, animated: true)
}
fetchItems()
NotificationCenter.default.addObserver(self, selector: #selector(managedObjectsDidChange), name: .NSManagedObjectContextObjectsDidChange, object: fervorController.persistentContainer.viewContext)
}
private func createDataSource() -> UICollectionViewDiffableDataSource<Section, NSManagedObjectID> {
@ -104,72 +92,58 @@ class ItemsViewController: UIViewController {
}
}
private func fetchItems() {
do {
let ids = try fervorController.persistentContainer.viewContext.fetch(fetchRequest)
var snapshot = NSDiffableDataSourceSnapshot<Section, NSManagedObjectID>()
snapshot.appendSections([.items])
snapshot.appendItems(ids, toSection: .items)
dataSource.apply(snapshot, animatingDifferences: false)
} catch {
let alert = UIAlertController(title: "Error fetching items", message: error.localizedDescription, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
present(alert, animated: true)
}
}
private var updateId = 0
@objc private func managedObjectsDidChange(_ notification: Notification) {
let id = updateId
updateId += 1
print("\(id) Managed objects did change")
let inserted = notification.userInfo?[NSInsertedObjectsKey] as? NSSet
let updated = notification.userInfo?[NSUpdatedObjectsKey] as? NSSet
let deleted = notification.userInfo?[NSDeletedObjectsKey] as? NSSet
// managed objectss from the notification are tied to the thread it was delivered on
// so get the published dates and evaluate the predicate here
let insertedItems = inserted?.compactMap { $0 as? Item }.filter { fetchRequest.predicate?.evaluate(with: $0) ?? true }.map { ($0, $0.published) }
let hasInsertedItems = inserted?.lazy.compactMap { $0 as? Item }.contains { fetchRequest.predicate?.evaluate(with: $0) ?? true } ?? false
if hasInsertedItems {
print("\(id) Has inserted items, skipping merge")
// if any items were inserted, just refetch everything. it's more expensive than it's worth to try and merge the changes into the current snapshot
self.fetchItems()
return
}
var snapshot = self.dataSource.snapshot()
// the itemIdentifiers getter takes a lot of time in profiles, so only call the getter once
let snapshotItems = snapshot.itemIdentifiers
if let updated = updated {
let knownUpdated = updated.compactMap { ($0 as? Item)?.objectID }.filter { snapshot.itemIdentifiers.contains($0) }
print("\(id) Updated: \(updated.count)")
let knownUpdated = updated.compactMap { ($0 as? Item)?.objectID }.filter { snapshotItems.contains($0) }
snapshot.reconfigureItems(knownUpdated)
}
if let deleted = deleted {
let knownDeleted = deleted.compactMap { ($0 as? Item)?.objectID }.filter { snapshot.itemIdentifiers.contains($0) }
print("\(id) Deleted: \(deleted.count)")
let knownDeleted = deleted.compactMap { ($0 as? Item)?.objectID }.filter { snapshotItems.contains($0) }
snapshot.deleteItems(knownDeleted)
}
if let insertedItems = insertedItems {
self.fervorController.persistentContainer.performBackgroundTask { ctx in
// for newly inserted items, the ctx doesn't have the published date so we check the data we got from the notification
func publishedForItem(_ id: NSManagedObjectID) -> Date? {
if let (_, pub) = insertedItems.first(where: { $0.0.objectID == id }) {
return pub
} else {
return (ctx.object(with: id) as! Item).published
}
}
// todo: this feels inefficient
for (inserted, insertedPublished) in insertedItems {
// todo: uhh, what does sql do if the published date is nil?
guard let insertedPublished = insertedPublished else {
snapshot.insertItems([inserted.objectID], beforeItem: snapshot.itemIdentifiers.first!)
continue
}
var index = 0
while index < snapshot.itemIdentifiers.count,
let pub = publishedForItem(snapshot.itemIdentifiers[index]),
insertedPublished < pub {
index += 1
}
// index is the index of the first item which the inserted one was published after
// (i.e., the item that should appear immediately after inserted in the list)
if index == snapshot.itemIdentifiers.count {
snapshot.appendItems([inserted.objectID], toSection: .items)
} else {
snapshot.insertItems([inserted.objectID], beforeItem: snapshot.itemIdentifiers[index])
}
}
DispatchQueue.main.async {
self.dataSource.apply(snapshot, animatingDifferences: false)
}
}
} else {
DispatchQueue.main.async {
self.dataSource.apply(snapshot, animatingDifferences: false)
}
}
print("\(id) Applying snapshot")
self.dataSource.apply(snapshot, animatingDifferences: false)
}
}