在迁移过程中添加和删除 Realm.Object

Question

我正在进行迁移，需要从领域中删除对象并将其替换为不同的类型。

简而言之，我以前只有一个类型，现在正在创建一个层次结构，所以 BaseItem 现在需要是一个 DerivedItem。

我不确定完成此任务的最佳方法。

这是我要尝试的方法：

setSchemaVersion(kSchemaVersion, Realm.defaultPath, { migration, oldSchemaVersion in
    if oldSchemaVersion == 0 {
        let realm = Realm()
        realm.write({ () -> Void in
            old = oldObject!    
            if old["type"] as! Int == 1 {
                let textItem = TextItem()
                textItem.text = old["text"] as! String
                copyBaseItemCommon(old, textItem)
                realm.add(textItem)
                realm.delete(newObject!)
     }
})

那些添加和删除是要走的路吗？

更新：

试过这个和第 3 行的代码死锁：let realm = Realm()

有人知道进行此类迁移的技术是什么吗？

Answer 1

您使用的是更新后的领域吗？

基于文档..

你应该这样做>>

 let realm = Realm()

 realm.write
{
 realm.add(theObject)
 realm.delete(theObject)
}

希望对您有所帮助！

Answer 2

当您下载 Realm 时，您有一个示例项目。打开它，你有一个迁移的演示。

他们是这样进行迁移的：

let migrationBlock: MigrationBlock = { migration, oldSchemaVersion in
    if oldSchemaVersion < 1 {
        migration.enumerate(Person.className()) { oldObject, newObject in
            if oldSchemaVersion < 1 {
                // combine name fields into a single field
                let firstName = oldObject!["firstName"] as! String
                let lastName = oldObject!["lastName"] as! String
                newObject?["fullName"] = "\(firstName) \(lastName)"
            }
        }
    }
}
setDefaultRealmSchemaVersion(1, migrationBlock)

如果您查看迁移文档，您会看到在迁移中有一些创建和删除的方法：

/**
    Create an `Object` of type `className` in the Realm being migrated.

    :param: className The name of the `Object` class to create.
    :param: object    The object used to populate the object. This can be any key/value coding
                      compliant object, or a JSON object such as those returned from the methods in
                      `NSJSONSerialization`, or an `Array` with one object for each persisted
                      property. An exception will be thrown if any required properties are not
                      present and no default is set.

    :returns: The created object.
    */
func create(className: String, value: AnyObject = default) -> RealmSwift.MigrationObject

/**
    Delete an object from a Realm during a migration. This can be called within
    `enumerate(_:block:)`.

    :param: object Object to be deleted from the Realm being migrated.
    */
func delete(object: RealmSwift.MigrationObject)

并且您可以像这样在迁移块中使用它们 migration.create("TextItem", oldObject!)。

请记住，在迁移中，您使用的是 migration 对象，而不是 Realm。

在迁移过程中添加和删除 Realm.Object

adding and removing Realm.Object during a migration

migration

realm

swift