ios - Realm - 如何删除没有任何关联对象的对象？

Question

在我的应用程序中，我从 Realm 加载存储的数据，然后调用 API 以获取用户对象的最新状态。之后，我过滤哪些对象是新的，哪些应该删除，如下所示:

// tracks is an array of objects downloaded from API and passed to the method
    let result = realm.objects(RealmTrack.self)

    print("Discovering new tracks")
    // Discover new tracks
    let new = tracks.filter({ track in
        !result.contains(where: { $0.trackUid == track.trackUid })
    })

    print("Discovering old tracks")
    // Discover old tracks in database
    let old = result.filter({ track in
        !tracks.contains(where: { $0.trackUid == track.trackUid })
    })

然后我正在向 Realm 执行写入事务，一切顺利，没有任何错误。

    print("Modifying database")
        try realm.write {
            //realm.create(RealmTrack.self, value: realms, update: .modified)
            realm.add(realms, update: Realm.UpdatePolicy.modified)
            //realm.add(realms)
            realm.delete(old)
        }

我的问题是每个 RealmTrack 可以有其他关联的 Realm 对象:

dynamic var _primaryAlbum: RealmAlbum?

dynamic var _primaryArtist: RealmArtist?

并且 RealmAlbum 和 RealmArtist 都有一个 RealmTrack 对象列表:

let tracks = List<RealmTrack>()

删除旧轨道后，如何获取没有任何关联 RealmTrack 的剩余 RealmAlbum 和 RealmArtist ？ 我也必须删除它们

我尝试的是在写事务 block 之后，检查哪些对象有空列表，但令人惊讶的是它总是0:

//realm.objects(RealmAlbum.self).count always returns 0 here
        let invalidatedAlbums = realm.objects(RealmAlbum.self).filter {
            $0.tracks.count == 0
            //$0.isInvalidated == true
        }

        let invalidatedArtists = realm.objects(RealmArtist.self).filter {
            $0.tracks.count == 0
            //$0.isInvalidated == true
        }

        try realm.write {
            realm.delete(invalidatedAlbums)
            realm.delete(invalidatedArtists)
        }

编辑:添加类声明

Realm 轨迹

@objcMembers class RealmTrack: Object, AWTrack {

        dynamic var _source: String = ""
        var source: AWMediaSource {
            return AWMediaSource(rawValue: _source)!
        }

        dynamic var _trackName: String = ""
        var trackName: String {
            return _trackName
        }

        dynamic var _trackUid: String = ""
        var trackUid: String {
            return _trackUid
        }

        dynamic var _playableUrl: String? = ""
        var playableUrl: String? {
            return _playableUrl
        }

        dynamic var _duration: TimeInterval = 0
        var duration: TimeInterval {
            return _duration
        }

        dynamic var _albumTrackNumber: Int = 0
        var albumTrackNumber: Int {
            return _albumTrackNumber
        }

        dynamic var _localizedTitle: String = ""
        var localizedTitle: String {
            return _localizedTitle
        }

        dynamic var _localizedAlbumTitle: String = ""
        var localizedAlbumTitle: String {
            return _localizedAlbumTitle
        }

        dynamic var _localizedAlbumArtist: String = ""
        var localizedAlbumArtist: String {
            return _localizedAlbumArtist
        }

        dynamic var _localizedArtist: String = ""
        var localizedArtist: String {
            return _localizedArtist
        }

        dynamic var _albumUid: String = ""
        var albumUid: String {
            return _albumUid
        }

        dynamic var _artistUid: String = ""
        var artistUid: String {
            return _artistUid
        }

        dynamic var _primaryAlbum: RealmAlbum?
        var primaryAlbum: AWAlbum? {
            return _primaryAlbum
        }

        dynamic var _primaryArtist: RealmArtist?
        var primaryArtist: AWArtist? {
            return _primaryArtist
        }

        override class func primaryKey() -> String? {
            return "_trackUid"
        }

真实相册

@objcMembers class RealmAlbum: Object, AWAlbum {

dynamic var _source: String = ""
var source: AWMediaSource {
    return AWMediaSource(rawValue: _source)!
}

dynamic var _albumName: String = ""
var albumName: String {
    return _albumName
}

dynamic var _albumUid: String = ""
var albumUid: String {
    return _albumUid
}

dynamic var _artistName: String = ""
var artistName: String {
    return _artistName
}

let tracks = List<RealmTrack>()

dynamic var _primaryArtist: RealmArtist?
var primaryArtist: AWArtist? {
    return _primaryArtist
}

override class func primaryKey() -> String? {
    return "_albumUid"
}

Realm 艺术家

@objcMembers class RealmArtist: Object, AWArtist {

dynamic var _source: String = ""
var source: AWMediaSource {
    return AWMediaSource(rawValue: _source)!
}

dynamic var _artistUid: String = ""
var artistUid: String {
    return _artistUid
}

dynamic var _artistName: String = ""
var artistName: String {
    return _artistName
}


let tracks = List<RealmTrack>()

override class func primaryKey() -> String? {
    return "_artistUid"
}

Answer 1

这个问题的全部范围对我来说有点不清楚，所以我可能不完全理解所问的内容，所以让我尝试回答这个问题:

How can I query for objects that have nothing in a list property.

如果您有一个对象具有其他对象的列表属性，如下所示:

class PersonClass: Object {
   @objc dynamic var person_name = ""
   let dogs = List<DogClass>()
}

class DogClass: Object {
   @objc dynamic var dog_name = ""
}

假设你有一个人的名单上有两只狗，然后还有一个人的名单上没有狗。您的目标是查询列表中没有狗的所有人员。

let personResults = realm.objects(PersonClass.self).filter("dogs.@count == 0")

@count 是列表和结果属性支持的聚合表达式。