[英]Core Data, how to remove one element from relationship's collection (NSSet)
我有很多核心数据 Model 如下,播放列表和歌曲。
我可以成功地将歌曲添加到播放列表的关系(歌曲)中,例如,播放列表 1(歌曲 1)-> 添加后,播放列表(歌曲 1,歌曲 2)。 如下代码所示,使用 addToSong(song) 方法,该方法由 CoreData 自动生成并用于将 object 添加到关系中。
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
// fetch selected playlist first
let fetchRequest = NSFetchRequest<Playlist>(entityName: "Playlist")
let currentCell = self.tableView.cellForRow(at: indexPath)
let cellText = currentCell?.textLabel?.text
print("cell text", cellText ?? "No Playlist Name")
let predicate = NSPredicate(format: "name = '\(cellText!)' ", "")
fetchRequest.predicate = predicate
let song = NSEntityDescription.insertNewObject(forEntityName: "Song", into: context) as! Song
song.songName = playingSong?.songName
song.artistName = playingSong?.artistName
song.albumName = playingSong?.albumName
song.fileURL = playingSong?.url
print("song name", playingSong?.songName ?? "no songName")
do {
let selectedPlaylists = try self.context.fetch(fetchRequest)
for item in selectedPlaylists {
item.addToSong(song)
}
} catch let error as NSError {
print("Could not delete. \(error), \(error.userInfo)")
}
navigationController?.popViewController(animated: true)
// show short alert message to user
showAlert(userMessage: "Song added")
}
但是当我尝试从播放列表的关系中删除一些歌曲以使用 removeFromSong(song) 时,它不起作用。 就我而言,我想做的是,例如,在播放列表 1(歌曲 1,歌曲 2,歌曲 3)之前和删除歌曲(xx)之后,播放列表 1(歌曲 2,歌曲 3)。 我确实搜索了网络,但没有找到如何找到要从关系中删除的特定 object,任何帮助都将不胜感激!
///在下面的代码中,我新建一首歌曲object,并赋予它两个属性songName和artistName,然后使用removeFromSong()将这首新创建的歌曲从播放列表的关系中删除,但不知道这种方式能否定位到正确的歌曲保存在关系中。
func deleteSong(indexPath: IndexPath) {
// remove record from Playlist entity of DB
let fetchRequest = NSFetchRequest<Playlist>(entityName: "Playlist")
let currentCell = self.tableView.cellForRow(at: indexPath)
// let cellText = currentCell?.textLabel?.text
let cellText = navigationItem.title
let predicate = NSPredicate(format: "name = '\(cellText!)' ", "")
fetchRequest.predicate = predicate
let song = NSEntityDescription.insertNewObject(forEntityName: "Song", into: context) as! Song
song.songName = currentCell?.textLabel?.text
song.artistName = currentCell?.detailTextLabel?.text
do {
let selectedPlaylists = try self.context.fetch(fetchRequest)
for item in selectedPlaylists {
// delete selected song in current playlist
item.removeFromSong(song)
// item.objectIDs(forRelationshipNamed: <#T##String#>)
// save the changes after deleting
try context.save()
}
} catch let error as NSError {
print("Could not delete. \(error), \(error.userInfo)")
}
// remove data from tableView
tableView.deleteRows(at: [indexPath], with: UITableView.RowAnimation.automatic)
//refresh tableView
tableView.reloadData()
}
///作为vadian的评论,将我的代码更改如下。
变化:
将关系的名称更新为歌曲和播放列表。
删除insertNewObject
的代码模式,现在首先从 Sony 实体中获取/查找所选歌曲。 然后从播放列表中删除该歌曲removeFromSong(song)
。
删除reloadData
,它不需要出现在deleteRow
之后。
问题:现在我可以通过滑动删除从 tableView 中删除选定的项目,但如果我强制关闭应用程序或导航到其他视图并返回,删除项目将被支持。 所以删除在核心数据 model 中不受影响。 当我使用下面的代码(例如添加歌曲)时,效果很好,所以删除的问题在哪里,任何提示都是合适的。
do {
let selectedPlaylists = try self.context.fetch(fetchRequest)
for item in selectedPlaylists {
// delete selected song in current playlist
print("Ready to remove!!!!!")
item.removeFromSongs(selectedSong[0])
// save the changes after deleting
try self.context.save()
}
} catch let error as NSError {
print("Could not delete. \(error), \(error.userInfo)")
}
///完整代码:
import UIKit
import CoreData
class ShowPlaylistDetailsViewController: UITableViewController {
var song: SongData?
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
var playlistObjects = [Playlist]()
var songObjects = [Song]()
var playlistName = ""
var selectedSong = [Song]()
// var rowCount: Int?
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
// set navigation controller's title
navigationItem.title = playlistName
// print("playlist name", playlistName)
let fetchRequest = NSFetchRequest<Playlist>(entityName: "Playlist")
let predicate = NSPredicate(format: "name = '\(playlistName)' ", "")
fetchRequest.predicate = predicate
do {
playlistObjects = try context.fetch(fetchRequest)
} catch {
fatalError("Can not query: \(error)")
}
songObjects = playlistObjects[0].songs?.allObjects as! [Song]
// refresh table data.
tableView.reloadData()
}
// MARK: - Table view data source
override func numberOfSections(in tableView: UITableView) -> Int {
// #warning Incomplete implementation, return the number of sections
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// print("songs count", songsCount!)
return songObjects.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "showPlaylistDetails", for: indexPath)
cell.textLabel?.text = songObjects[indexPath.row].songName
cell.detailTextLabel?.text = songObjects[indexPath.row].artistName
cell.imageView?.image = UIImage(named: "icons8-music-50")
cell.imageView?.layer.cornerRadius = 0.8
return cell
}
override func tableView(_ tableView: UITableView, trailingSwipeActionsConfigurationForRowAt indexPath: IndexPath) -> UISwipeActionsConfiguration? {
let deleteAction = UIContextualAction(style: .normal, title: "Delete", handler: { (action, view, completion) in
self.deleteSong(indexPath: indexPath)
})
// action.image = UIImage(named: "My Image")
deleteAction.backgroundColor = .red
let swipeActions = UISwipeActionsConfiguration(actions: [deleteAction])
swipeActions.performsFirstActionWithFullSwipe = false
return swipeActions
}
func deleteSong(indexPath: IndexPath) {
// find current selected cell
let currentCell = self.tableView.cellForRow(at: indexPath)
// find the deleted song
let fetchRequestForSong = NSFetchRequest<Song>(entityName: "Song")
let ssName = currentCell?.textLabel?.text
print("ssName", ssName ?? "Song name retrieve failed")
let predicateForSong = NSPredicate(format: "songName = '\(ssName ?? "Song name retrieve failed")' ", "")
fetchRequestForSong.predicate = predicateForSong
do {
selectedSong = try self.context.fetch(fetchRequestForSong)
// print("songName", selectedSong.first?.songName)
} catch let error as NSError {
print("Could not delete. \(error), \(error.userInfo)")
}
// find current selected playlist
let fetchRequest = NSFetchRequest<Playlist>(entityName: "Playlist")
let cellText = navigationItem.title
let predicate = NSPredicate(format: "name = '\(cellText!)' ", "")
fetchRequest.predicate = predicate
do {
let selectedPlaylists = try self.context.fetch(fetchRequest)
for item in selectedPlaylists {
// delete selected song in current playlist
print("Ready to remove!!!!!")
item.removeFromSongs(selectedSong[0])
// save the changes after deleting
try self.context.save()
}
} catch let error as NSError {
print("Could not delete. \(error), \(error.userInfo)")
}
// remove song from dataSource array
songObjects.remove(at: indexPath.row)
// remove data from tableView
tableView.deleteRows(at: [indexPath], with: UITableView.RowAnimation.automatic)
}
@IBAction func naviBack(_ sender: UIBarButtonItem) {
navigationController?.popViewController(animated:true)
}
}
根据我的评论,这是删除方法的清理版本,如果removeFromSongs
确实从关系中删除了歌曲,它应该可以工作
func deleteSong(at indexPath: IndexPath) {
// get current selected song
let currentSong = songObjects[indexPath.row]
// find current selected playlist
let fetchRequest = NSFetchRequest<Playlist>(entityName: "Playlist")
let cellText = navigationItem.title
let predicate = NSPredicate(format: "name == %@", cellText!)
fetchRequest.predicate = predicate
fetchRequest.fetchLimit = 1
do {
if let selectedPlaylist = try self.context.fetch(fetchRequest).first {
print("Ready to remove!!!!!")
selectedPlaylist.removeFromSongs(currentSong)
// save the changes after deleting
try self.context.save()
// remove song from dataSource array
songObjects.remove(at: indexPath.row)
// remove data from tableView
tableView.deleteRows(at: [indexPath], with: .automatic)
}
} catch {
print("Could not delete.", error)
}
}
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