Hibernate关系注释

Question

假设我有学生，并且想要为每个学生映射一个房子。

说实体1：Student_master表被描述为（student_id数据（primary_key），标准，等级，年龄）

说实体2：house_master表被描述为（house_id（primary_key），house_color_house_capacity）

说实体3：student_house_mapping表是（student_house_id，Student_id（foreign_key），house_id（foreign_key））。

现在我在这里有过每个学生穿越并获取其内部细节，

例如，我得到了学生，现在通过student_house_mapping表我得到的house_id并用它，我得到一个特定的house_master对象。

如何在Hibernate中可以使用这个关系来实现（例如：一对一，多对一）的注解，如果我对所有的实体类，我用

Answer 1

定义

joinColumns = {@JoinColumn(...)}, 
inverseJoinColumns = {@JoinColumn(...)}) 

参数在它自己的列

通过阅读第一句话，我可以说这是OneToOne，正如你所说每个学生都有一所房子。

如果你考虑一个场景，每个学生可以有很多房子。 然后，这种关系将是OneToMany，并且只有两个表的学生和学生拥有OneToMany与House（POJO班级）的房子。

如果你认为连房子都可以属于很多学生。 然后，你应该去ManyToMany与你目前的表学生，房屋和students_house表（桥表）。

Student.java

@Entity 
@Table(name="students") 
public class Student { 
private int studentId;// set the column name with @JoinColumn annotation if you want 
private int standard;// to be different from the variable name 
private int grade; 
private int age; 
@OneToMany 
@JoinTable(name="students_houses", 
    joinColumns = @JoinColumn(name="studentId"), 
    inverseJoinColumns = @JoinColumn(name="houseId")) 
private List<House> houses; 
// getters and setters 
} 

House.java

@Entity 
@Table(name="houses") 
public class House { 
private int houseId; 
private String color; 
private int houseCapacity; 
@OneToMany 
@JoinTable(name="students_houses", 
    joinColumns = @JoinColumn(name="houseId"), 
    inverseJoinColumns = @JoinColumn(name="studentId")) 
private List<Student> students; 
// getters and setters 
} 

如果你想比这两个表中，你可以的外键与其它附加字段创建自定义的表桥创建一个自定义Bridge类，每个类具有OneToMany和Bridge类。和Bridge类有两个类的ManyToOne。

您可以参阅计算器文档进行进一步的例子

Answer 2

一种方法一直是@JoinTable注解。 简单的例子：

@ManyToMany 
@JoinTable(name = "student_house_mapping") 
private List<Student> students; 

如果Hibernate无法找到正确的加入（有时是这种情况），你有@JoinTable太

Answer 3

Assuming Student and House has ManyToMany relationship, you can design something like this: 

    package com.raf.prac.domain; 

    import javax.persistence.*; 
    import java.util.HashSet; 
    import java.util.Set; 


    @Entity 
    @Table(name = "student") 
    public class Student { 
     @Id 
     @GeneratedValue(strategy = GenerationType.AUTO) 
     private int student_id; 
     @Column(name = "standard") 
     String standard; 
     @Column(name = "grade") 
     String grade; 
     @Column(name = "age") 
     int age; 

     @ManyToMany 
     @JoinTable(name = "student_house_mapping", 
       joinColumns = {@JoinColumn(name = "student_id")}, 
       inverseJoinColumns = {@JoinColumn(name = "house_id")}) 
     private Set<House> houses = new HashSet(); 

     public Student() { 
     } 

     public String getStandard() { 
      return standard; 
     } 

     public void setStandard(String standard) { 
      this.standard = standard; 
     } 

     public String getGrade() { 
      return grade; 
     } 

     public void setGrade(String grade) { 
      this.grade = grade; 
     } 

     public int getAge() { 
      return age; 
     } 

     public void setAge(int age) { 
      this.age = age; 
     } 

     public Set<House> getHouses() { 
      return houses; 
     } 

     public void setHouses(Set<House> houses) { 
      this.houses = houses; 
     } 
    } 

package com.raf.prac.domain; 

import javax.persistence.*; 
import java.util.HashSet; 
import java.util.Set; 

/** 
* Created by ar on 22/08/2016. 
*/ 
@Entity 
@Table(name = "house") 
public class House { 
    @Id 
    @GeneratedValue(strategy = GenerationType.AUTO) 
    private int house_id; 
    @Column(name = "house_color") 
    private String house_color; 
    @Column(name = "house_capacity") 
    private int house_capacity; 

    @ManyToMany(mappedBy = "houses") 
    Set<Student> students = new HashSet(); 

    public House() { 
    } 

    public int getHouse_id() { 
     return house_id; 
    } 

    public void setHouse_id(int house_id) { 
     this.house_id = house_id; 
    } 

    public String getHouse_color() { 
     return house_color; 
    } 

    public void setHouse_color(String house_color) { 
     this.house_color = house_color; 
    } 

    public int getHouse_capacity() { 
     return house_capacity; 
    } 

    public void setHouse_capacity(int house_capacity) { 
     this.house_capacity = house_capacity; 
    } 

    public Set<Student> getStudents() { 
     return students; 
    } 

    public void setStudents(Set<Student> students) { 
     this.students = students; 
    } 
}