对于多个映射，外键必须具有与引用主键相同的列数

Question

嗨，下面是我的实体，它们之间有许多联系

大学生JAVA

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

    @Id
    @Column(name = "UserID")
    private String userid;

    @ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.LAZY)
    @JoinColumns({
       @JoinColumn(name = "userrole", referencedColumnName = "VALUE"),
       @JoinColumn(name = "userrole", referencedColumnName = "DESCRIPTION")

    })
    private studentdetails userrole;

//setters and getters 
//constructor

}

学生详细信息。JAVA

@Data
@Entity
@Table(name = "student_details")
public class studentdetails {

    @Id
    @Column(name = "VALUE")
    private String value;

    @Id
    @Column(name = "DESCRIPTION")
    private String description;

   //setters and getters 
   //constructor
}

appmain.java

public static void main()
{

//session configuration

studentdetails  sd = new studentdetails();
sd.setvalue("abc");
sd.setdescription("abcdef");

student student1 = new student();
student.setuserid("1");
student.userrole(sd);

student student2 = new student();
student.setuserid("2");
student.userrole(sd);

session.save(student1 );
session.save(student2 );


}

下面是我的2表中的列

student: 

UserID
userrole

student_details:

VALUE
DESCRIPTION

“学生详细信息”中的“值”应输入学生表的“用户角色”

但当我执行appmain时，我的错误率就降低了

org.hibernate.MappingException: Foreign key (FK6D56043A4415BDB5:student [userrole])) must have same number of columns as the referenced primary key (student_details [VALUE,DESCRIPTION])
    at org.hibernate.mapping.ForeignKey.alignColumns(ForeignKey.java:113)
    at org.hibernate.mapping.ForeignKey.alignColumns(ForeignKey.java:96)
    at org.hibernate.cfg.Configuration.secondPassCompileForeignKeys(Configuration.java:1354)
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1261)
    at org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:383)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1377)
    at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:954)

我试图解决这个问题，但它显示出同样的错误请建议我如何解决这个问题

Answer 1

要解决此问题，请按如下方式更改代码：

 @ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.LAZY)
    @JoinColumns({
       @JoinColumn(name = "userrole_value", referencedColumnName = "VALUE"),
       @JoinColumn(name = "userrole_desc", referencedColumnName = "DESCRIPTION")

    })
    private studentdetails userrole;

问题原因：在制图中：

@JoinColumns({
       @JoinColumn(name = "userrole", referencedColumnName = "VALUE"),
       @JoinColumn(name = "userrole_desc", referencedColumnName = "DESCRIPTION")

    })

您正在告诉hibernate在名为userrole的Student实体表中创建一个外键，该外键引用了StudentDetails实体表中名为VALUE的列。

然后在下一行中，您再次告诉hibernate在StudentDetails中使用与FKey相同的列名称--userrole，作为列DESCRIPTION，因此这一行覆盖了前一行。

所以hibernate看到您正试图在映射到StudentDetails实体表的StudentDetails实体表中使用一列作为外键。但是StudentDetails表的复合键由两列组成，因此hibernate会抛出一个异常。

org.hibernate.MappingException: Foreign key (FK6D56043A4415BDB5:student [userrole])) must have same number of columns as the referenced primary key (student_details [VALUE,DESCRIPTION])

其他信息：

您正试图为实体StuentMore声明一个复合ID，因此该实体应该包含Serializable接口，这是强制性的。现在，这个复合Id类应该重写equals（）和hashcode（）方法。

建议您尝试遵循实体和字段的Java命名约定。