swift - 使用 LInkingOjbects 的 Realm 在运行时出现 fatal error

Question

出现以下 fatal error 。

fatal error: 'try!' expression unexpectedly raised an error: Error Domain=io.realm Code=1 "Schema validation failed due to the following errors: - Property 'GearModel.category' declared as origin of linking objects property 'CategoryRepository.gearList' links to type 'CategoryModel'" UserInfo={NSLocalizedDescription=Schema validation failed due to the following errors: - Property 'GearModel.category' declared as origin of linking objects property 'CategoryRepository.gearList' links to type 'CategoryModel', Error Code=1}:

此处的对象模型:齿轮模型仅分配给一个类别

import Foundation
import RealmSwift

class GearModel: Object{

    dynamic var gearID = NSUUID().uuidString
    dynamic var name = ""
    dynamic var manufacturer = ""
    dynamic var sortOrder = 0
    dynamic var category: CategoryModel?

    override class func primaryKey() -> String? {return "gearID"}
    }

类别模型:尝试获取分配了类别的所有 GearModel 项目的列表。

    import Foundation
    import RealmSwift

    class CategoryModel: Object{

        dynamic var categoryID = NSUUID().uuidString
        dynamic var sortOrder = 0
        dynamic var name = ""
        let gearList = LinkingObjects(fromType: GearModel.self, property: "category")

override class func primaryKey() -> String? {return "categoryID"}
    }

Category Repository 类:allCategories() 函数中的“let realm =...”行发生 fatal error

import Foundation
import RealmSwift

class CategoryRepository: CategoryModel{

    class func GetGearItemsForCategory(CategoryID: String) -> Results<GearModel>
    {
        let realm = try! Realm()

        var gearItems = realm.objects(GearModel.self)

        let predicate = NSPredicate(format: "categoryID = %@", CategoryID)
        gearItems = gearItems.filter(predicate)
        return gearItems
    }

    class func GetCountOfGearItems(CategoryID: String) -> Int
    {
        let realm = try! Realm()

        var gearItems = realm.objects(GearModel.self)

        let predicate = NSPredicate(format: "categoryID = %@", CategoryID)
        gearItems = gearItems.filter(predicate)
        return gearItems.count
    }

    class func AddCategory(CategoryID: String, Name: String, SortOrder: Int){

        let realm = try! Realm()

        let category = CategoryModel(name: CategoryID, categoryID: Name, sortOrder: SortOrder)

        try! realm.write {
            realm.add(category)
        }
    }

    class func allCategories() -> Results<CategoryModel> {

        let realm = try! Realm()


        return realm.objects(CategoryModel.self).sorted(byProperty: "SortOrder")
    }

Answer 1

不支持从具有 LinkingObjects 属性的类继承。

Realm 中的 Object 和 List 属性不是协变的，这意味着它们只能指向指定的类，而不能指向该类的子类。这意味着 GearModel.category 无法链接到 CategoryRepository 对象，但是 CategoryRepository 具有正在尝试继承的 gearList 属性列出链接到它的 GearModel 对象。

在您的特定情况下，尚不清楚为什么 CategoryRepository 继承自 CategoryModel。