使用Objectify 4获取实体密钥

问题描述

我需要对这种实体进行getKey()

I need to do getKey() with this kind of Entity:

@Entity
public class Value {
    @Id
    private long id;
    private byte[] value;

    com.googlecode.objectify.Key<Value> getKey() {
        return com.googlecode.objectify.Key.create(Value.class, id); // When executed this line throws NullPointerException
    }

        // Code omitted
}

但是我之前在版本3中使用的模式似乎不再适用.@Transient替换为@Ignore，但是当我用@Ignore注释getKey()函数时，出现此错误:

However the pattern I used before with version 3 seems to be not applicable anymore.The @Transient is replaced by @Ignore but when I annotate my getKey() function with @Ignore I get this error:

The annotation `@Ignore` is disallowed for this location

所以我只是注释掉了.看看是否能正常工作.

So I just commented it out. And see if it will work.

此外，

运行我的应用程序时，getKey()函数会如上所述抛出NullPointerException.

When I run my application the getKey() function throws NullPointerException as commented above.

那么，获取@Entity键的方式是什么?

So, what is the pattern to get a @Entity key?

推荐答案

您不能创建具有null或0 id的Key. Objectify和数据存储区都不允许.

You can't create a Key with a null or 0 id. Neither Objectify nor the datastore will allow it.

如果要从实体创建密钥，请确保首先具有有效的ID.

If you want to create a Key from an entity, make sure it has a valid id first.

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