嵌入式实体从存储为Blob的原始数据读取 [英] Embedded entity reading from originaly stored as Blob

问题描述

从AppEngine低级数据存储区API迁移到对象5:读取Entity会出错.

Migrating from AppEngine low level Datastore API to objectify 5: reading Entity gets an error.

我使用数据存储区实体工具看到的是因为旧数据保留了"Ifont".为"斑点"而是应该成为"嵌入式类"

What i see using the Datastore Entity Tool is because the old data keeps "Ifont" as "Blob" instead and should become an "Embedded class"

@Entity(name = "Mandant")
public class Mandant implements IsSerializable {
        @Id
    private Long id;
    @Index
    private String nr = "";
    private Ifont fontHeader;

我们如何读取此Blob数据?

How do we read this Blob data?

推荐答案

首先如何将数据保存到Blob字段中?Blob只是一个字节数组；可能是任何东西.如果您使用Java序列化写出了Ifont(看起来很可能来自您的示例)，这很容易-只需像下面这样声明该字段即可:

How did you save the data into a Blob field in the first place? A Blob is just a byte array; it could be anything. If you wrote the Ifont out using Java serialization (seems likely from your example), this is easy - just declare that field like this:

private @Serialize Ifont fontHeader;

这将保留Blob结构.但是，如果您实际上希望将其存储为EmbeddedEntity，则需要迁移数据.这里有一些建议的策略:

That will preserve the Blob structure. However, if you actually want it stored as EmbeddedEntity, you'll need to migrate the data. There are some strategies suggested here:

https://github.com/objectify/objectify/wiki/SchemaMigration

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