一对多关系核心数据获取数据

Posted 2023-03-13

【中文标题】一对多关系核心数据获取数据

【英文标题】：One to Many Relationship Core Data fetch Data

【发布时间】：2018-03-02 18:39:11

【问题描述】：

关于这个主题有很多问题，但我无法解决。

在 vadian 的这个答案中，他通过两个重复循环获得了值：

swift 3 - core data relationship - fetch data https://***.com/a/43846785/8887336

它不适用于我的代码，我不知道为什么。

这是我的代码：

import Foundation
import CoreData

struct HobbiesCollection 
  let typ: String
  let location: String



class LoadData
  class func load(context: NSManagedObjectContext) 
    let persons = ["Owen", "Greg"]
    let futbal = HobbiesCollection(typ: "futbal", location: "stadium")
    let swimming = HobbiesCollection(typ: "swimming", location: "pool")
    let collection = [persons[0]: swimming, persons[1]: futbal]

    for x in collection 
      let person = Person(context: context)
      let hobbiesCD = Hobbies(context: context)
      person.name = x.key
      hobbiesCD.typ = x.value.typ
      hobbiesCD.location = x.value.location

      person.addToToHobbies(hobbiesCD)

      do 
        try context.save()
       catch let error 
        print(error.localizedDescription)
      
    

    let fetch: NSFetchRequest<Person> = Person.fetchRequest()
    var result = [Person]()
    do 
      result = try context.fetch(fetch)
     catch let error 
    print(error.localizedDescription)
    
    for y in result 
      print("Persons:", y.name!)
      for x in y.toHobbies! 
        let location = x.location Error: "Value of type 'Any' has no member 'location'"
      
    
  

我得到错误：

“任何”类型的值没有成员“位置”

我的两个核心数据类：

extension Person 

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Person> 
        return NSFetchRequest<Person>(entityName: "Person")
    

    @NSManaged public var name: String?
    @NSManaged public var toHobbies: NSSet?



// MARK: Generated accessors for toHobbies
extension Person 

    @objc(addToHobbiesObject:)
    @NSManaged public func addToToHobbies(_ value: Hobbies)

    @objc(removeToHobbiesObject:)
    @NSManaged public func removeFromToHobbies(_ value: Hobbies)

    @objc(addToHobbies:)
    @NSManaged public func addToToHobbies(_ values: NSSet)

    @objc(removeToHobbies:)
    @NSManaged public func removeFromToHobbies(_ values: NSSet)


extension Hobbies 

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Hobbies> 
        return NSFetchRequest<Hobbies>(entityName: "Hobbies")
    

    @NSManaged public var typ: String?
    @NSManaged public var location: String?
    @NSManaged public var toPerson: Person?

我还有一个关于谓词的问题。 如果我像这样进行谓词提取：

fetch.predicate = NSPredicate(格式: "name = %@", person1)

如果在我的示例中我有多个爱好，是否可以使用第二个谓词参数来获取所有具有位置 = 体育场的爱好，而不是使用 for 循环来查找具有位置 = person1 的体育场的这些爱好？

【参考方案1】：

toHobbies 属性是 Any 的 NSSet，因此您需要对它或循环中的每个 x 进行类型转换。

对于谓词，您可以使用诸如“toHobbies.location = %@”之类的键路径