在CloudKit中查询引用的最佳方法？ [英] Best way to query references in CloudKit?

问题描述

假设我的CloudKit数据库中有2个实体：

Say I have 2 entities in my CloudKit database:

- Album
  - (NSString) title

- Photo
  - (NSString) name
  - (CKRefrence) album

照片的相册参考为CK。这意味着1张相册可以包含许多照片（按预期方式）。

Photos have a CKReference to an Album. This means that 1 album can have many photos (as expected).

我有一个屏幕，我想在其中显示所有相册，以及每个相册中有多少张照片。对此进行查询的最佳方法是什么？如果我现在查询相册，则每个相册对其照片一无所知。

I have a screen where I want to display all albums, and how many photos are in each album. What is the best way to query for this? If I query for Albums right now, each album knows nothing about its photos.

推荐答案

对于每个相册对象anAlbum，您将形成谓词并查询Photo记录类型，如下所示：

For each of the album object anAlbum, you would form your predicate and query the Photo record type like so:

let predicate = NSPredicate(format: "album == %@", anAlbum)
let query = CKQuery(recordType: "Photo", predicate: predicate)

在completionHandler中，您可以获取结果数组的计数，这就是属于相册的照片数量。

In the completionHandler, you can get a count of the result array, which would be the number of Photos belonging to anAlbum.

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