外键必须有相同数量为多对一映射被引用的主键列

Question

嗨下面是我的实体，它们之间的关联多对一

student.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 

} 

studentdetails.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

都在我的2台

student: 

UserID 
userrole 

student_details: 

VALUE 
DESCRIPTION 

在“student_details”应该进入学生表

的“UserRole的”“价值”，但是当我执行我的appmain我收到以下错误列

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，但它显示同样的错误 请建议我如何解决这个

Answer 1

要解决此问题，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; 

原因问题：在映射：

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

    }) 

你告诉Hibernate来创建Student实体表的外键被称为userrole指的是StudentDetails实体表中名为VALUE的列。

然后在接下来的行中，您再次告诉休眠使用相同的柱面名称 - userrole作为FKey在StudentDetails中的列DESCRIPTION，所以此行覆盖了前一个。

因此，hibernate会发现您试图将单个列作为外键在Student实体表中映射到StudentDetails实体表。但StudentDetails表具有由2列组成的复合键，因此hibernate会引发异常。

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：

您试图声明一个复合的ID为实体StudentDetails，所以这个实体应该implelemt Serializable接口，这是强制性的。 现在这个复合Id类应该覆盖equals()和hashcode()方法。

只是一个建议，尝试遵循您的实体和字段的Java命名约定。