Hibernate 如何在中间表中添加列

发布于 2024-12-01 12:39:44 字数 505 浏览 1 评论 0原文

详细信息如下。

我有 2 个具有一对多关系的实体表。

首先，Exam类有很多Category类。 Hibernate 生成此表

______________
Exam
- Id
- Name 
- Category
______________
Category
- Id
- Name
______________
Exam_Category
- Exam_Id
- Category_Id

我需要在 Exam_Category 表中添加额外的列例如：

______________
Exam_Category
- Exam_Id
- Category_Id
* User_Id

我将如何实现这一目标。如果有的话，我将如何获得 user_id 值，因为 Exam_Category 未公开。谢谢

原文

Here's the details.

I have 2 entity tables with one to many relationship.

First, Exam class has many Category class. Hibernate generates this tables

______________
Exam
- Id
- Name 
- Category
______________
Category
- Id
- Name
______________
Exam_Category
- Exam_Id
- Category_Id

I need to add an extra column in Exam_Category table
ex:

______________
Exam_Category
- Exam_Id
- Category_Id
* User_Id

How am i going to accomplish this. if ever, how will i also get the user_id value because the Exam_Category is not exposed. Thanks

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倒数 2024-12-08 12:39:44

做到这一点的最佳方法是使用元素集合。

@Entity
public class Exam {
    @CollectionOfElements(fetch = FetchType.LAZY)
    @JoinTable(name = "EXAM_CATEGORY", joinColumns = @JoinColumn(name = "FK_EXAM"))
    public Set<CategoryEntry> getCategories() {
        return this.categories;
    }
}

@Embeddable
public class CategoryEntry{

    private Category category;
    private User user;

    @ManyToOne
    @JoinColumn(name = "FK_CATEGORY", nullable = false)
    public Category getCategory() {
        return this.category;
    }

    @ManyToOne
    @JoinColumn(name = "FK_USER", nullable = false)
    public User getUser() {
        return this.user;
    }

// ... setters and such

}

@Entity
public class Category {
}

这种方法比将其映射为实体更清晰，因为从逻辑上讲，它本来就不是一个实体。

然后，您可以在 Exam 中添加一些其他方法来获取所有类别（不包括用户）或将其作为地图检索，等等。如果需要，您可以通过封装完全隐藏此中间对象。

The best way to do this is to use a collection of elements.

@Entity
public class Exam {
    @CollectionOfElements(fetch = FetchType.LAZY)
    @JoinTable(name = "EXAM_CATEGORY", joinColumns = @JoinColumn(name = "FK_EXAM"))
    public Set<CategoryEntry> getCategories() {
        return this.categories;
    }
}

@Embeddable
public class CategoryEntry{

    private Category category;
    private User user;

    @ManyToOne
    @JoinColumn(name = "FK_CATEGORY", nullable = false)
    public Category getCategory() {
        return this.category;
    }

    @ManyToOne
    @JoinColumn(name = "FK_USER", nullable = false)
    public User getUser() {
        return this.user;
    }

// ... setters and such

}

@Entity
public class Category {
}

This approach is cleaner than mapping it as an entity, since, logically, it is not an entity to begin with.

Then you can add some other methods in Exam to get all the categories (without the users) or to retrieve it as a map, or whatever. You can completely hide this intermediate object through encapsulation, if that is required.

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