Question

我的核心数据项目中有2个实体：Land和Coordinate。一块土地可以有很多坐标，所以它有一对多的关系。

为了保存我的土地及其坐标，我这样做：

func saveToDataBase() {

   let landName:String = String(describing: Land.self)

    let land:Land = NSEntityDescription.insertNewObject(forEntityName: landName, into: DatabaseController.getContext()) as! Land


    land.id = 1
    land.area = myLandArray[2]
    land.perimeter = myLandArray[3]
    land.lat = myLandArray[0]
    land.long = myLandArray[1]

    let coordName:String  = String(describing: Coordinate.self)
    let coord:Coordinate = NSEntityDescription.insertNewObject(forEntityName: coordName, into: DatabaseController.getContext()) as! Coordinate

        for i in 0..<points.count {
            coord.lat = points[i].latitude
            coord.long = points[i].longitude
            land.addToRelationship(coord)  //add coordinates to its land
        }

    DatabaseController.saveContext()

    }

我得到了这样的土地：

func showLands() {

    let fetchRequest:NSFetchRequest<Land> = Land.fetchRequest()

    do{
        let searchResults = try DatabaseController.getContext().fetch(fetchRequest)
        print("Number of results: \(searchResults.count)")

        for result in searchResults as [Land]{
            print("ID: \(result.id)")
            print("Lat: \(result.lat)")
            print("Long: \(result.long)")
            print("Area: \(result.area) \(result.unArea!)")
            print("Perimeter: \(result.perimeter) \(result.unPerimeter!)")


        }
    }
    catch{
        print("Error: \(error)")
    }
 }

如何获得每块土地的坐标？我尝试了一些没有成功的事情：（

以下是我的课程：

public class Coordinate: NSManagedObject {

}


extension Coordinate {

@nonobjc public class func fetchRequest() -> NSFetchRequest<Coordinate> {
    return NSFetchRequest<Coordinate>(entityName: "Coordinate");
    }

@NSManaged public var id: Int64
@NSManaged public var lat: Double
@NSManaged public var long: Double
@NSManaged public var relationship: Land?

 }



public class Land: NSManagedObject {

}



    extension Land {

@nonobjc public class func fetchRequest() -> NSFetchRequest<Land> {
    return NSFetchRequest<Land>(entityName: "Land");
}

@NSManaged public var area: Double
@NSManaged public var attachment: NSData?
@NSManaged public var id: Int64
@NSManaged public var lat: Double
@NSManaged public var long: Double
@NSManaged public var perimeter: Double
@NSManaged public var relationship: NSSet?

}

// MARK: Generated accessors for relationship
extension Land {

@objc(addRelationshipObject:)
@NSManaged public func addToRelationship(_ value: Coordinate)

@objc(removeRelationshipObject:)
@NSManaged public func removeFromRelationship(_ value: Coordinate)

@objc(addRelationship:)
@NSManaged public func addToRelationship(_ values: NSSet)

@objc(removeRelationship:)
@NSManaged public func removeFromRelationship(_ values: NSSet)

}

访问核心数据中的实体

0 个答案: