领域获取结果控制器

Question

我是 Realm 的新手，之前使用过 Core Data。据我了解，NSFetchedResultsController 的类似物是以下代码：

    observationToken = realm.objects(DBMessage.self).observe { (changes) in
        switch changes {
        case .initial(let messages):
            print("fetched - \(Array(messages))")
        case .update(let results, deletions: let deletions, insertions: let insertions, modifications: let modifications):
            let updates = Array(results)
            print("updates started - \(Thread.isMainThread)")
            insertions.forEach({
                print("updates - \(updates[$0])")
            })
            print("updates finished")
        case .error(let error):
            print("observation error - \(error.localizedDescription)")
        }
    }

但问题是case .initial 领域从数据库中获取所有对象。有没有办法在不获取所有缓存对象的情况下为特定类型和谓词的对象设置通知？提前致谢。

Answer 1

当然，您可以在应用过滤器和排序后声明集合观察：

// just an example
observationToken = realm.objects(DBMessage.self)
    .filter("isRead == false")
    .sort(byKeyPath: "insertedAt", ascending: false)
    .observe { [weak self] changes in
        switch changes {
        case .initial(let messages):
            // initial collection
            break
        case .update(_, let deletions, let insertions, let modifications):
            break
        case .error(let error):
            print(error)
        }
    }