自引用@OneToMany

Question

我有以下class

@Entity
public class Comment extends Base {

@ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private Comment inReplyTo;

@OneToMany(mappedBy = "inReplyTo", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private Collection<Comment> replies;

public Comment() {
}

public Collection<Comment> getReplies() {
    return replies;
}

public void setReplies(Collection<Comment> comments) {
    this.replies = comments;
}

public Comment getInReplyTo() {
    return inReplyTo;
}

public void setInReplyTo(Comment inReplyTo) {
    this.inReplyTo = inReplyTo;
}

}

添加新评论并设置 inReplyTo 有效，评论将保存到数据库中。但是 inReplyTo 评论的回复字段为空。

也在做

c.setReplies(new ArrayList<Comment>());
c.getReplies().add(x);
repo.save(c);

导致此错误

org.datanucleus.store.types.IncompatibleFieldTypeException: Incompatible type requested for field "Comment.replies" : was java.util.Collection but should be java.util.Collection

有什么想法吗？

Answer 1

您应该设置关系的两个部分：

c.setReplies(new ArrayList<Comment>());
c.getReplies().add(x);
c.setInReplyTo(x);//this is the most imporant
repo.save(c);

如果这不起作用，则可能是 Datanucleus 中的错误：尝试报告它并在此处的某处放置 link。

Answer 2

如果我没有正确理解你的问题，你的代码类似于：

Comment parent = //...

Comment reply = new Comment();
reply.setInReplyTo(parent);
reply = commentRepository.save(reply);

Collection<Comment> parentReplies = parent.getReplies();

并且您想知道为什么 parentReplies 是 null。

这是意料之中的，因为 JPA 2.0 规范的 §2.9 实体关系说：

Note that it is the application that bears responsibility for maintaining the consistency of runtime relationships—for example, for insuring that the “one” and the “many” sides of a bidirectional relationship are consistent with one another when the application updates the relationship at runtime.

DataNucleus 不负责实例化包含新 reply 评论的新集合以及将 parent 的回复属性设置到该集合。我已经检查了 DataNucleus 4.1.0 和 Hibernate 4.3.10 并确认它们都不会更新评论中的回复属性.

您的应用程序需要确保运行时关系是一致的。例如，您可以将 addReply() 方法添加到 Comment class:

    public void addReply(Comment reply) {
        if (this == reply) throw new IllegalArgumentException("`reply' cannot be `this' Comment object because a comment cannot be a reply to itself.");
        if (replies == null) replies = new ArrayList<>();
        replies.add(reply);
        reply.setInReplyTo(this);
    }

那么添加回复的代码将类似于：

Comment parent = //...

Comment reply = new Comment();
parent.addReply(reply);
reply = commentRepository.save(reply);

Collection<Comment> parentReplies = parent.getReplies();

此外，我没有重现错误：

org.datanucleus.store.types.IncompatibleFieldTypeException: Incompatible type requested for field "Comment.replies" : was java.util.Collection but should be java.util.Collection

Answer 3

我升级到 DataNucleus 4.1.1，进行了清理并开始工作。

自引用@OneToMany

Self referencing @OneToMany

jpa

datanucleus

spring-data