Realm 迁移中的转换错误 属性 Double to List<CustomObject>

Question

我需要的是创建一个迁移，根据以下代码将 discount:Double 更改为 discounts:List<Discount>()。

这是现有对象：这是我的 Realm Object 现在的样子。

class Item:Object{
    @objc dynamic var itemName:String = "Some Name"
    @objc dynamic var discount:Double = 0 // need to change this property
}

以下是我尝试进行更改的方式。

新对象：

class Discount: Object {
    @objc dynamic var name:String = "Discount Name"
    @objc dynamic var discount:Double = 0.0
}

修改对象具有one-to-many关系。

class Item:Object{
    @objc dynamic var itemName:String = "Some Name"
    let discounts = List<Discount>()
}

迁移

    Realm.Configuration.defaultConfiguration = Realm.Configuration(
        schemaVersion: 3,
        migrationBlock: { migration, oldSchemaVersion in
            if (oldSchemaVersion < 3) {
                migration.enumerateObjects(ofType: Item.className()) { oldObject, newObject in

                    let oldDiscount = oldObject!["discount"] as! Double

                    let discount = Discount()
                    discount.amount = oldDiscount

                    let discounts = newObject!["discounts"] as! List<Discount>
                    discounts.append(discount)
            }
        }
    })

我遇到错误：

Could not cast value of type RealmSwift.List<RealmSwift.DynamicObject>(0x1c8910068) to RealmSwift.List<AppName.Discount> (0x1c890f6a0).

同样，问题是，我如何创建迁移以将 discount:Double 更改为 discounts:List<Discount>()？

Answer 1

您可以将折扣 ​​属性 作为 [oldDiscount]

之类的列表迁移到新的折扣列表中

这是代码。我重命名了一些对象以使其更加清晰，因为重新使用单词 'discount' 来指代 class 和 属性 令人困惑。

let vers = UInt64(1)
let config = Realm.Configuration( schemaVersion: vers, migrationBlock: { migration, oldSchemaVersion in
     if (oldSchemaVersion < vers) {
         print("performing migration")
         migration.enumerateObjects(ofType: ItemClass.className()) { oldItem, newItem in
            let oldDiscount = oldItem!["discount"] as? Double ?? 0.0

            let d = DiscountClass()
            d.name = "Test"
            d.discount = oldDiscount

            newItem!["discountList"] = [d]
         }
     } else {
        print("no migration needed")
    }
 })