新 RealmList 中字符串字段的领域迁移

Question

对话 class 之前有一个名为 "message" 的字符串字段。现在这个 "message" 字段被删除，我在 Conversation class 中添加了一个 "RealmList allMessages" 而不是旧的 "message" 字段。 ChatMessage class 有一个字段名称 "messageText"。我如何将 "message" 从对话 class 迁移到列表 "allMessages" 的 "messageText"？

public class ChatMessage extends RealmObject implements Parcelable {

    ....

    private String messageText;

    ....
}

旧对话class。

public class Conversation extends RealmObject implements Parcelable{

    private String message;
    ....
}

新对话class。

public class Conversation extends RealmObject implements Parcelable{

     private RealmList<ChatMessage> allMessages;
}

我试过了。但它不起作用。

        if (oldVersion == 6){
            RealmObjectSchema messageSchema = schema.create("ChatMessage")
                .addField("messageText", String.class);

        RealmObjectSchema userChatSchema = schema.get("Conversation");
        if (userChatSchema != null) {
            userChatSchema.addRealmListField("message_tmp", messageSchema)
                    .transform(new RealmObjectSchema.Function() {
                        @Override
                        public void apply(@NonNull DynamicRealmObject obj) {
                            String message = obj.getString("message");
                            RealmList<DynamicRealmObject> valueObj = obj.getList("message_tmp");
//What next?Am i right till this point??



                        }
                    })
                    .removeField("message")
                    .renameField("message_tmp", "allMessages");
        }
    }

Answer 1

RealmObjectSchema messageSchema = schema.create("ChatMessage")
                .addField("txt", String.class);

        RealmObjectSchema userChatSchema = schema.get("Conversation");
        if (userChatSchema != null) {
            userChatSchema.addRealmListField("message_tmp", messageSchema)
                    .transform(new RealmObjectSchema.Function() {
                        @Override
                        public void apply(@NonNull DynamicRealmObject obj) {
                            String message = obj.getString("message");


                            RealmList<DynamicRealmObject> valueObj = obj.getList("message_tmp");
                            DynamicRealmObject dynamicRealmObject = realm.createObject("ChatMessage");
                            if (message != null)
                                dynamicRealmObject.set("txt", message);
                            else
                                dynamicRealmObject.set("txt", "This message has been deleted");

                            valueObj.add(dynamicRealmObject);

                        }
                    })
                    .removeField("message")
                    .renameField("message_tmp", "allMessages");
        }

Answer 2

我的用例有点不同。我有一个 RealmList<RealmString>，我想迁移到 RealmList<String>

这是我的迁移：

// delete all RealmString from the database because they should be replaced with String
// RealmString is used to create lists of strings
if (oldVersion == 56L) {

    // convert RealmList<RealmString> into RealmList<String>
    fun RealmObjectSchema.migrateToListOfStringPrimitives(fieldName: String) {
        addRealmListField("${fieldName}_tmp", String::class.java)
        transform { obj ->
            val realmListOfRealmStrings = obj.getList(fieldName)
            val realmListOfStrings = obj.getList("${fieldName}_tmp", String::class.java)
            realmListOfRealmStrings.mapTo(realmListOfStrings) { it.getString("value") }
        }
        removeField(fieldName)
        renameField("${fieldName}_tmp", fieldName)
    }

    schema[Assessment::class.java.simpleName]!!
        .migrateToListOfStringPrimitives("bodyPartInjured")

    schema[R2PProtocol::class.java.simpleName]!!
        .migrateToListOfStringPrimitives("sports")

    schema[NoteAssessment::class.java.simpleName]!!
        .migrateToListOfStringPrimitives("images")

    // delete all dangling RealmStings from DB
    schema.remove("RealmString")

    oldVersion++;
}