我如何使用hibernate注释创建外键约束？ [英] How can I create a foreign key constraint using hibernate annotations?

问题描述

我有两个表，每个表都有一个主键User和Question。

  @Entity 
 @Table（name =USER）
 public class User 
 {
 @Id 
 @Column（name =user_id）
 @GeneratedValue（strategy = GenerationType.AUTO）
 private long ID; 
 
 @Column（name =username）
 private String username; 
 
 // getter and setter 
} 
  

问题表。

  @Entity 
 @Table（name =QUESTION）
 public class Questions extends BaseEntity {
 
 @Id 
 @Column（name =question_id）
 @GeneratedValue（strategy = GenerationType.AUTO）
 private int id; 
 
 @Column（name =question_text）
 private String question_text; 
 
 // getter and setter 
 
} 
  

我还有一个表UserAnswer，它具有userId和questionId作为上述两个表中的外键。

但我无法找到如何引用这些

  @Entity 
 @Table（name =UserAnswer）
 public class UserAnswer 
 {
 
 @Column（name =user_id）
 private用户用户; 
 
 // @ ManyToMany 
 @Column（name =question_id）
私人提问; 
 
 @Column（name =response）
 private String response; 
 
 // getter and setter 
} 
  

请帮助我做到这一点？
在此先感谢。

解决方案

@Column 不是适当的注释。您不希望将整个用户或问题存储在列中。你想创建一个实体之间的关联。首先将问题更改为问题，因为一个实例代表单个问题，而不是几个问题。然后创建关联：

  @Entity 
 @Table（name =UserAnswer）
 public class UserAnswer {
 
 //这个实体需要一个ID：
 @Id 
 @Column（name =useranswer_id）
 @GeneratedValue（strategy = GenerationType.AUTO） 
私人长ID; 
 
 @ManyToOne 
 @JoinColumn（name =user_id）
私人用户用户; 
 
 @ManyToOne 
 @JoinColumn（name =question_id）
私人问题问题; 
 
 @Column（name =response）
 private String response; 
 
 // getter and setter 
} 
  

Hibernate文档解释了这一点。阅读。并阅读注释的javadoc。

I am trying to use hibernate annotation for writing a model class for my database tables.

I have two tables each having a primary key User and Question.

@Entity
@Table(name="USER")
public class User 
{
    @Id
    @Column(name="user_id")
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    @Column(name="username")
    private String username;

    // getter and setter
}

Question Table.

@Entity
@Table(name="QUESTION")
public class Questions extends BaseEntity{

    @Id
    @Column(name="question_id")
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;

    @Column(name="question_text")
    private String question_text;

    // getter and setter

}

And I have one more table, UserAnswer, which has userId and questionId as foreign keys from the above two tables.

But I am unable to find how I can reference these constraints in the UserAnswer table.

@Entity
@Table(name="UserAnswer ")
public class UserAnswer 
{

    @Column(name="user_id")
    private User user;

    //@ManyToMany
    @Column(name="question_id")
    private Questions questions ;

    @Column(name="response")
    private String response;

    //getter and setter 
}

Please help me achieve this? Thanks in advance.

解决方案

@Column is not the appropriate annotation. You don't want to store a whole User or Question in a column. You want to create an association between the entities. Start by renaming Questions to Question, since an instance represents a single question, and not several ones. Then create the association:

@Entity
@Table(name = "UserAnswer")
public class UserAnswer {

    // this entity needs an ID:
    @Id
    @Column(name="useranswer_id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;

    @ManyToOne
    @JoinColumn(name = "question_id")
    private Question question;

    @Column(name = "response")
    private String response;

    //getter and setter 
}

The Hibernate documentation explains that. Read it. And also read the javadoc of the annotations.

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