ios - 使用 fetchrequest 谓词过滤掉某些核心数据项。

Question

所以我有两个实体。列表和评论。一个列表可以有多个关联的评论。

extension Listing {

    @NSManaged var listingTitle: String?
    @NSManaged var comments: NSSet?
    @NSManaged var listingLatitude: Double
    @NSManaged var listingLongitude: Double
}

extension Comment {

    @NSManaged var comment: String?
    @NSManaged var commentId: String?
    @NSManaged var rating: Int32
    @NSManaged var username: String?
    @NSManaged var listing: Listing?

}

使用 NSPredicate 我可以很容易地过滤掉位于特定地理区域的列表。

// Fetching data from CoreData
            let fetchRequest = NSFetchRequest()
            fetchRequest.predicate = NSPredicate(format: "listingLatitude BETWEEN {%f,%f} AND listingLongitude BETWEEN {%f,%f}", (latitude-0.10), (latitude+0.10), (longitude-0.10), (longitude+0.10))
            let entity = NSEntityDescription.entityForName("Listing", inManagedObjectContext: self.mainMoc)
            fetchRequest.entity = entity

            fetchRequest.sortDescriptors = [sortDescriptor]

            do {
                listings = try self.mainMoc.executeFetchRequest(fetchRequest) as! [Listing]

            }

这工作正常，但我如何完成过滤掉所有带有给定特定评级的评论的列表？

Answer 1

由于 comments 是一对多关系，您需要帮助 CoreData 确定您关注的是它们中的哪一个:ALL、ANY 或 NONE。例如:

fetchRequest.predicate = NSPredicate(format: "ANY comments.rating > 4")

将仅包括那些 Listings，其任何 Comments 的评级为 4 或更高，而:

fetchRequest.predicate = NSPredicate(format: "ALL comments.rating < 2")

仅当所有 Comments 的评分都低于 2 时才会包括它们。