Question

我查看了Realm网站上的文档，找不到任何描述如何在迁移中处理删除属性的内容。我采用了一组彼此非常相似的属性，并将它们移至新对象。像这样：

class MyObject: Object {
    @objc dynamic var siteName = ""
    @objc dynamic var lat = 0.0
    @objc dynamic var lon = 0.0
    @objc dynamic var roadNames = ""
    @objc dynamic var startTime = ""
    @objc dynamic var endTime = ""
    @objc dynamic var comments: String = ""
    @objc dynamic var complete: Bool = false
}

然后我将其更改为：

class Site: Object {
    @objc dynamic var siteName = ""
    @objc dynamic var lat = 0.0
    @objc dynamic var lon = 0.0
    @objc dynamic var roadNames = ""
} 

class MyObject: Object {
    @objc dynamic var site: Site?
    @objc dynamic var startTime = ""
    @objc dynamic var endTime = ""
    @objc dynamic var comments: String = ""
    @objc dynamic var complete: Bool = false
}

我的移民是

let block: MigrationBlock = { (migration: Migration, oldSchemaVersion) in
    if oldSchemaVersion < 1 {
        migration.enumerateObjects(ofType: MyObject.className()) { oldObject, newObject in
            newObject!["siteName"] = oldObject!["siteName"]
            newObject!["lat"] = oldObject!["lat"]
            newObject!["lon"] = oldObject!["lon"]
            newObject!["roadNames"] = oldObject!["roadNames"]

            // Delete old properties.
        }
    }
}

我的迁移应如何删除属性？

Answer 1

如果阅读Realm guide on migrations，您会在其中一个代码块的注释中看到它说：

        // Nothing to do!
        // Realm will automatically detect new properties and removed properties
        // And will update the schema on disk automatically

因此您不必担心删除属性，因为它们会自动删除。

不过，您需要担心的是如何迁移其他值。您应该为每个Site创建一个MyObject并为该Site分配属性，我在这里看不到您在做的事情。有关如何在迁移块中创建新的Site的信息，请参见this question。

您的迁移块应类似于：

migration.enumerateObjects(ofType: MyObject.className()) { oldObject, newObject in
    let site = migration.create(Site.className())
    site["siteName"] = oldObject!["siteName"]
    site["lat"] = oldObject!["lat"]
    site["lon"] = oldObject!["lon"]
    site["roadNames"] = oldObject!["roadNames"]
    newObject!["site"] = site
}

迁移期间删除属性

1 个答案: