如何防止RealmSwift列表中的重复？

Question

如何防止在列表中添加重复项RealmSwift？

我将我User作为领域对象,但真正的数据源是服务器(只需使用Realm本地缓存用户).当我从服务器获取当前用户数据时,我想确保我在realm中存储的用户具有来自服务器的所有播放列表(以及它们与轨道列表等同步).我很担心如果我从服务器上循环遍历那些列表myUser.playlists,那么我可能会多次将相同的播放列表添加到用户的播放列表列表中.

class User: Object {
    
    dynamic var name = ""
    dynamic var id = ""
    let playlists = List<Playlist>()
    override class func primaryKey() -> String {
        return "id"
    }
}

class Playlist: Object {
    
    dynamic var name = ""
    dynamic var id = ""
    let tracks = List<Song>()
    override class func primaryKey() -> String {
        return "id"
    }
}

class Song: Object {
    
    dynamic var title = ""
    let artists = List<Artist>()
    dynamic var id = ""
    override class func primaryKey() -> String {
        return "id"
    }
}

class Artist: Object {
    dynamic var name = ""
    dynamic var id = ""
    override class func primaryKey() -> String {
        return "id"
    }
}

Answer 1

这取决于来自服务器的数据类型.如果始终显示整个播放列表数据(您始终可以替换现有的播放列表数据),则可以将列表删除为空,然后附加它们.

realm.write {
    user.playlists.removeAll() // empty playlists before adding

    for playlistData in allPlaylistData {
        let playlist = Playlist()
        ...
        user.playlists.append(playlist)
    }
}

如果来自服务器的差异数据(也有一些是重复的),则必须检查数据是否已存在.

realm.write {
    for playlistData in allPlaylistData {
        let playlist = Playlist()
        ...

        realm.add(playlist, update: true) // Must add to Realm before check

        guard let index = user.playlists.indexOf(playlist) else {
            // Nothing to do if exists
            continue
        }
        user.playlists.append(playlist)
    }
}