我有两个具有多对一关系的表,但它们没有外键。
像 Student
有很多,而 Teacher
就是一个,
实体例如:
@Entity
@Table(name = "student")
class Student {
@Column(name = "TeacherName")
private String teacherName;
@ManyToOne
private Teacher teacher
}
@Entity
@Table(name = "teacher")
class Teacher {
private String name;
}
当我查询学生时,sql是:
select * from Student as st INNER JOIN Teacher as tcr ON st.TeacherName = tcr.name;
我发现 @ManyToOne
不能工作,看起来它需要一个外键。虽然该表无法提供此类信息。
谁能告诉我如何配置实体?
最佳答案
您必须使用以下映射:
public class Teacher {
@OneToMany(mappedBy = "teacher")
private Set<Student> students;
@Column(name = "name")
private String name;
}
public class Student {
@ManyToOne
@JoinColumn(name = "teacherName", referencedColumnName = "name")
private Teacher teacher;
}
然后在 HQL 中:
select s from Student s INNER JOIN s.teacher t where t.name = :name
或者 如果您想保留当前的映射,则需要在 hql 中使用“旧”样式的连接来实现非外键列的连接:
select s from Student s, Teacher t where t.name = s.teacherName and t.name = :name
关于java - 如何让jpa hibernate创建具有多对一但没有外键的实体,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/42106500/