所以我有两个实体。清单和评论。一个列表可以有多个关联的注释。
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内的列表。
// 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]
}
这可以正常工作,但是我如何完成过滤掉所有带有给定特定等级的注释的清单?
最佳答案
由于comments
是一对多关系,因此您需要帮助CoreData找出您所关注的对象:ALL,ANY或NONE。因此,例如:
fetchRequest.predicate = NSPredicate(format: "ANY comments.rating > 4")
将仅包含其
Listings
的任何一项被评为4或更高的那些Comments
,而:fetchRequest.predicate = NSPredicate(format: "ALL comments.rating < 2")
仅当所有
Comments
的额定值小于2时,才会包括它们。