JPA OneToMany 和 ManyToOne throw:实体列映射中的重复列(应映射为 insert=“false" 更新=“false") [英] JPA OneToMany and ManyToOne throw: Repeated column in mapping for entity column (should be mapped with insert="false" update="false")

问题描述

我有三个类，其中一个名称是 User，这个用户有其他类实例.像这样;

I have three classes one of the names is User and this user has other classes instances. Like this;

public class User{
    @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL)
    public List<APost> aPosts;

    @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL)
    public List<BPost> bPosts;
}




   public class BPost extends Post {
    
    @ManyToOne(fetch=FetchType.LAZY)    
    public User user;
 }
    
    public class APost extends Post {
    
     @ManyToOne(fetch=FetchType.LAZY) 
     public User user;
 }

它是这样工作的，但在数据库中生成空表.其中必须包含外键.当我尝试使用 mappedBy 和 JoinColumn 注释时，我失败了.我该如何解决?

it's working like this but generates empty tables in DB. Which have to contain foreign keys. When I tried to use mappedBy and JoinColumn annotations I got failed. How can I resolve this?

额外信息:

当我改变了;

 @ManyToOne(fetch=FetchType.LAZY)
 @JoinColumn(name="id")
 public User user;

和

 @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL, mappedBy="id")
 public List<APost> aPosts;

我要了

发生 JPA 错误(无法构建 EntityManagerFactory):实体映射中的重复列:models.post.APost 列:id(应映射为 insert=false"；更新=false")

A JPA error occurred (Unable to build EntityManagerFactory): Repeated column in mapping for entity: models.post.APost column: id (should be mapped with insert="false" update="false")

最终最后，我对 JPA 注释完全错误.:(当我改变

Final Finally, I was totally wrong about JPA annotations. :( When I change

@OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL, mappedBy="id")

到

@OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL, mappedBy="user")

和

@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name="user_id")

一切正常.:)

推荐答案

你永远不应该使用单向的 @OneToMany 注释，因为:

You should never use the unidirectional @OneToMany annotation because:

1. 它会生成低效的 SQL 语句
2. 它会创建一个额外的表，从而增加数据库索引的内存占用

现在，在您的第一个示例中，双方都拥有关联，这很糟糕.

Now, in your first example, both sides are owning the association, and this is bad.

虽然@JoinColumn 会让@OneToMany 一方负责关联，但这绝对不是最好的选择.因此，始终在 @OneToMany 端使用 mappedBy 属性.

While the @JoinColumn would let the @OneToMany side in charge of the association, it's definitely not the best choice. Therefore, always use the mappedBy attribute on the @OneToMany side.

public class User{
    @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL, mappedBy="user")
    public List<APost> aPosts;

    @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL, mappedBy="user")
    public List<BPost> bPosts;
}

public class BPost extends Post {

    @ManyToOne(fetch=FetchType.LAZY)    
    public User user;
}

public class APost extends Post {

     @ManyToOne(fetch=FetchType.LAZY) 
     public User user;
}

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