Hibernate註解開發詳解

時間 2019-12-13

原文原文鏈接

*****************關於註解的簡單介紹html

詳細介紹請點擊這裏註解詳細教程java

package com.tomowork.pojo;

import org.hibernate.annotations.GenericGenerator;

import javax.annotation.Generated;
import javax.persistence.*;
import java.io.Serializable;

@Entity() //代表這個類是一個實體類，在數據庫中存在對應的字段
@Table(name="emp",schema = "test") //在數據庫中對應的表
public class Emp implements Serializable {
    private Integer empno ;
    private String ename ;
    @Id
    /**
     * 可選的主鍵的生成策略
     * 可選的值：
     TABLE,
     SEQUENCE, //主要用於Oracle數據庫
     IDENTITY,
     AUTO; //根據數據庫定義主鍵生成策略，myql底層是自動增加主列
     @GeneratedValue(strategy = GenerationType.AUTO)
     */
    /**
     * 若是主鍵是指派的，就不能用jpa註解
     */
    @GeneratedValue(generator = "deptno") //定義一個主鍵生成策略
    @GenericGenerator(name = "deptno",strategy = "assigned")
    public Integer getEmpno() {
        return empno;
    }

    public void setEmpno(Integer empno) {
        this.empno = empno;
    }
    @Column(name = "ename")
    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }
}

****************註解開發單向一對一mysql

　　編寫數據庫腳本：linux

　　　　假如一個學生只有一部手機，一個手機只屬於一個學生；sql

CREATE TABLE `phone` (
  `tel` varchar(255) NOT NULL DEFAULT '' COMMENT '手機號碼',
  `pname` varchar(255) NOT NULL COMMENT '手機名字',
  `price` double NOT NULL COMMENT '手機價格',
  `sid` int(11) NOT NULL COMMENT '手機的主人',
  PRIMARY KEY (`tel`),
  KEY `fk_sid` (`sid`),
  CONSTRAINT `fk_sid` FOREIGN KEY (`sid`) REFERENCES `students` (`sid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `students` (
  `sid` int(11) NOT NULL DEFAULT '0',
  `sname` varchar(255) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  PRIMARY KEY (`sid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

　　編寫實體類：數據庫

　　　　Students.java後端

package com.itcloud.pojo;

import org.hibernate.annotations.GenericGenerator;

import javax.persistence.*;

@Entity //代表這是一個數據庫實體
@Table(name="Students")
public class Students {
    //統一代碼規範將註解設置在get方法上面而不是設置在屬性上面
    private Integer sid ;
    private String sname ;
    private Integer age ;
    //無參構造
    public Students(){}
    //全參構造
    public Students(Integer sid, String sname, Integer age) {
        this.sid = sid;
        this.sname = sname;
        this.age = age;
    }

    @Id //表示這是一個主鍵列
    //定義主鍵的生成策略,assigned表示是本身指派的
    @GeneratedValue(generator = "sid")
    @GenericGenerator(name="sid",strategy = "assigned")
    public Integer getSid() {
        return sid;
    }

    public void setSid(Integer sid) {
        this.sid = sid;
    }

    /**
     *Basic,定義屬性的存取獲取策略
     *Basic(FetchType.EAGER):默認，表示即時存取
     *Basic(FetchType.LAZY)：延遲加載
     */
    @Basic //這裏設置默認就能夠了
    @Column(length =13,name="sname" )
    public String getSname() {
        return sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }
    @Basic
    @Column(name = "age")
    public Integer getAge() {
        return age;
    }

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

　　Phone.javasession

package com.itcloud.pojo;

import org.hibernate.annotations.GenericGenerator;

import javax.persistence.*;

@Entity
@Table(name="phone",schema = "test")
public class Phone {
    private String tel ;
    private String pname ;
    private Double price ;
    private Students students ;

    public Phone() {
    }

    public Phone(String tel, String pname, Double price, Students students) {
        this.tel = tel;
        this.pname = pname;
        this.price = price;
        this.students = students;
    }

    @Id
    @GeneratedValue(generator = "tel")
    @GenericGenerator(name = "tel",strategy="assigned") //本身指派主鍵生成策略
    public String getTel() {
        return tel;
    }

    public void setTel(String tel) {
        this.tel = tel;
    }
    @Basic
    @Column(name="pname")
    public String getPname() {
        return pname;
    }

    public void setPname(String pname) {
        this.pname = pname;
    }
    @Basic
    @Column(name="price")
    public Double getPrice() {
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    /**
     *進行單項一對一的關聯映射
     */

    @OneToOne(cascade = CascadeType.ALL) //所有級聯CRUD操做
    @JoinColumn(name="sid",unique = true) //name指的是主表的外鍵,unique表示是不是惟一的
    public Students getStudents() {
        return students;
    }

    public void setStudents(Students students) {
        this.students = students;
    }
}

　　測試用例：mybatis

package com.itcloud.test;

import com.itcloud.pojo.Phone;
import com.itcloud.pojo.Students;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.After;
import org.junit.Test;

public class TestHibernate {
    public static SessionFactory sessionFactory =null ;
    public static Session session = null ;
    public static Transaction transaction ;
    static {
        Configuration configuration = new Configuration().configure() ;
        sessionFactory = configuration.buildSessionFactory() ;
        session = sessionFactory.openSession() ;
        transaction = session.beginTransaction() ;
    }
    @Test
    public void post(){
        //建立學生實體
        Students stus = new Students(201401,"張三",10) ;
        Phone phone = new Phone("13588578866","iphone",888.36,stus) ;
        session.save(stus) ;
        session.save(phone) ;
    }

    @After
    public void destroy(){
        transaction.commit();
        session.close();
        sessionFactory.close();
    }
}

　　測試結果：app

Hibernate: 
    insert 
    into
        Students
        (age, sname, sid) 
    values
        (?, ?, ?)

Hibernate: 十二月 02, 2017 12:19:41 上午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
    insert 
    into

        phoneINFO: HHH10001008: Cleaning up connection pool [jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8]
        (pname, price, sid, tel) 
    values
        (?, ?, ?, ?)

***********註解開發一對一雙向

數據庫表結構

CREATE TABLE `students` (
`sid` int(11) NOT NULL,
`sname` varchar(15) NOT NULL DEFAULT '',
`age` int(11) NOT NULL DEFAULT '0',
`tel` varchar(18) NOT NULL DEFAULT '' COMMENT '一個學生有一部手機',
PRIMARY KEY (`sid`),
KEY `fk_tel` (`tel`),
CONSTRAINT `fk_tel` FOREIGN KEY (`tel`) REFERENCES `phone` (`tel`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `phone` (
`tel` varchar(18) NOT NULL,
`pname` varchar(20) NOT NULL DEFAULT '' COMMENT '手機名字',
`price` double NOT NULL DEFAULT '0' COMMENT '手機價格',
PRIMARY KEY (`tel`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

　　　　假如一個學生擁有一個手機，一個手機屬於一個學生，學生爲主控方

　　　　實體類的編寫

　　　　　　Students

package com.itcloud.pojo;

import org.hibernate.annotations.GenericGenerator;

import javax.persistence.*;
import java.io.Serializable;

@Entity //代表這是一個數據庫實體
@Table(name="students")
public class Students implements Serializable {
    //統一代碼規範將註解設置在get方法上面而不是設置在屬性上面
    private Integer sid ;
    private String sname ;
    private Integer age ;
    private Phone phone  ;//一個學生擁有一個手機
    //無參構造
    public Students(){}
    //全參構造
    public Students(Integer sid, String sname, Integer age) {
        this.sid = sid;
        this.sname = sname;
        this.age = age;
    }

    @Id //表示這是一個主鍵列
    //定義主鍵的生成策略,assigned表示是本身指派的
    @GeneratedValue(generator = "sid")
    @GenericGenerator(name="sid",strategy = "assigned")
    public Integer getSid() {
        return sid;
    }

    public void setSid(Integer sid) {
        this.sid = sid;
    }

    /**
     *Basic,定義屬性的存取獲取策略
     *Basic(FetchType.EAGER):默認，表示即時存取
     *Basic(FetchType.LAZY)：延遲加載
     */
    @Basic //這裏設置默認就能夠了
    @Column(name="sname" )
    public String getSname() {
        return sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }
    @Basic
    @Column(name = "age")
    public Integer getAge() {
        return age;
    }

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


   @OneToOne(cascade = CascadeType.ALL,fetch = FetchType.LAZY)
   @JoinColumn(name="tel",unique = true)  //name指的是主表的外鍵，數據庫中的外鍵,unique表示是不是惟一的
    public Phone getPhone() {
        return phone;
    }
    public void setPhone(Phone phone) {
        this.phone = phone;
    }
}

　　　　Phones.java

 1 package com.itcloud.pojo;
 2 
 3 import org.hibernate.annotations.GenericGenerator;
 4 
 5 import javax.persistence.*;
 6 import java.io.Serializable;
 7 
 8 @Entity
 9 @Table(name="phone",schema = "test")
10 public class Phone implements Serializable {
11     private String tel ;
12     private String pname ;
13     private Double price ;
14 
15     private Students students ; //一個手機屬於一個學生
16 
17     public Phone() {
18     }
19 
20     public Phone(String tel, String pname, Double price) {
21         this.tel = tel;
22         this.pname = pname;
23         this.price = price;
24     }
25 
26     @Id
27     @GeneratedValue(generator = "tel")
28     @GenericGenerator(name = "tel",strategy="assigned") //本身指派主鍵生成策略
29     public String getTel() {
30         return tel;
31     }
32 
33     public void setTel(String tel) {
34         this.tel = tel;
35     }
36     @Basic
37     @Column(name="pname")
38     public String getPname() {
39         return pname;
40     }
41 
42     public void setPname(String pname) {
43         this.pname = pname;
44     }
45     @Basic
46     @Column(name="price")
47     public Double getPrice() {
48         return price;
49     }
50 
51     public void setPrice(Double price) {
52         this.price = price;
53     }
54 
55     @OneToOne(mappedBy = "phone",fetch = FetchType.LAZY) //主表類中的從表實例
56     public Students getStudents() {
57         return students;
58     }
59 
60     public void setStudents(Students students) {
61         this.students = students;
62     }
63 }

測試用例：

  @Test
    public void post(){
        //建立學生實體
        Phone phone = new Phone("13588578867","iphone",888.36) ;
        Students stus = new Students(201402,"李四",10) ;
        stus.setPhone(phone);
        phone.setStudents(stus);
        session.save(phone) ; //必定要保存手機，再保存學生
        session.save(stus) ;
    }

雙向一對一總結：

　　首先表設計：主表：students,存在有phone的外鍵

　　　　　　　　從表：沒有外鍵，數據交給students管理；

　　實體類的設計：主表：　　　　　　　　

　　　　　　　　　　@OneToOne(cascade = CascadeType.ALL,fetch = FetchType.LAZY) 　　　　　　　　 @JoinColumn(name="tel",unique = true) //name指的是主表的外鍵，數據庫中的外鍵,unique表示是不是惟一的

　　　　　　　　　從表：

　　　　@OneToOne(mappedBy = "phone",fetch = FetchType.LAZY) //phone爲主表類中的從表實例即：private Phone phone ;中的phone

　***********單方多對一關聯關係：

　　假設一個部門擁有多個僱員，一個僱員屬於一個部門，典型的多對一關聯

　　　首先表設計：　　

CREATE TABLE `dept` (
  `deptno` int(11) NOT NULL DEFAULT '0',
  `dname` varchar(255) DEFAULT '',
  `loc` varchar(255) DEFAULT '',
  PRIMARY KEY (`deptno`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `emp` (
  `empno` int(11) NOT NULL,
  `ename` varchar(15) NOT NULL DEFAULT '' COMMENT '僱員姓名',
  `job` varchar(25) NOT NULL DEFAULT '' COMMENT '僱員職位',
  `deptno` int(11) NOT NULL DEFAULT '-1' COMMENT '所屬部門，-1表示沒有部門',
  PRIMARY KEY (`empno`),
  KEY `fk_deptno` (`deptno`),
  CONSTRAINT `fk_deptno` FOREIGN KEY (`deptno`) REFERENCES `dept` (`deptno`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

實體類的編寫

　　Dept.java(多方)

package com.itcloud.pojo;

import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
@Entity
/**
 * @author:itcloud
 *
 */
public class Dept {
    private Integer deptno;
    private String dname;
    private String loc;

    public Dept() {
    }

    public Dept(Integer deptno, String dname, String loc) {
        this.deptno = deptno;
        this.dname = dname;
        this.loc = loc;
    }

    @Id
    @Column(name = "deptno")
    public int getDeptno() {
        return deptno;
    }

    public void setDeptno(int deptno) {
        this.deptno = deptno;
    }

    @Basic
    @Column(name = "dname")
    public String getDname() {
        return dname;
    }

    public void setDname(String dname) {
        this.dname = dname;
    }

    @Basic
    @Column(name = "loc")
    public String getLoc() {
        return loc;
    }

    public void setLoc(String loc) {
        this.loc = loc;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {return true;}
        if (o == null || getClass() != o.getClass()){ return false;}

        Dept dept = (Dept) o;

        if (deptno != dept.deptno) {return false;}
        if (dname != null ? !dname.equals(dept.dname) : dept.dname != null) {return false;}
        if (loc != null ? !loc.equals(dept.loc) : dept.loc != null) {return false;}

        return true;
    }

    @Override
    public int hashCode() {
        int result = deptno;
        result = 31 * result + (dname != null ? dname.hashCode() : 0);
        result = 31 * result + (loc != null ? loc.hashCode() : 0);
        return result;
    }

    @Override
    public String toString() {
        return "Dept{" +
                "deptno=" + deptno +
                ", dname='" + dname + '\'' +
                ", loc='" + loc + '\'' +
                '}';
    }
}

Emp.java（一方）

package com.itcloud.pojo;

import org.hibernate.annotations.GenericGenerator;

import javax.persistence.*;

@Entity
@Table(name = "emp",schema = "test")
public class Emp {

    private Integer empno ;
    private String ename  ;
    private String job ;

    private Dept dept ;

    public Emp() {
    }

    public Emp(Integer empno, String ename, String job, Dept dept) {
        this.empno = empno;
        this.ename = ename;
        this.job = job;
        this.dept = dept;
    }

    /**
     * emp是多方，dept是一方
     *
     */
    @ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.EAGER) //抓取策略是積極的
    @JoinColumn(name = "deptno")//deptno是外鍵
    public Dept getDept() {
        return dept;
    }

    public void setDept(Dept dept) {
        this.dept = dept;
    }

    @Id
    @GeneratedValue(generator = "empno")
    @GenericGenerator(name="empno",strategy = "assigned")
    public Integer getEmpno() {
        return empno;
    }

    public void setEmpno(Integer empno) {
        this.empno = empno;
    }
    @Column(name="ename")
    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }
    @Column(name="job")
    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }
}

測試用例：

    @Test
    public void post(){
        //多對一測試
        Dept dept = new Dept(11,"運維部門","402");
        Emp emp = new Emp(7371,"clom","linux運維",dept) ;
        session.save(dept) ;
        session.save(emp) ;
    }

測試結果：

Hibernate: 
    insert 
    into
        Dept
        (dname, loc, deptno) 
    values
        (?, ?, ?)
Hibernate: 
    insert 
    into
        emp
        (deptno, ename, job, empno) 
    values
        (?, ?, ?, ?)

多對一在多方（即Emp.java）上面添加以下註解

...   
 /**
     * emp是多方，dept是一方
     *
     */
    @ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.EAGER) //抓取策略是積極的
    @JoinColumn(name = "deptno")//deptno是外鍵
    public Dept getDept() {
        return dept;
    }
...

***********一對多單向外鍵關聯

一方持有多方的集合：一個部門存在多個僱員，可是僱員不是重複的，在Dept.java中添加：private Set<Emp> allEmps = new HashSet<>() ;

數據表：仍是dept,emp這兩個表

編寫實體類

Dept.java

package com.itcloud.pojo;

import org.hibernate.annotations.GenericGenerator;

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

@Entity
@Table(name = "dept")
public class Dept {

    private Integer deptno ;
    private String dname ;
    private String loc ;

    private Set<Emp> emps = new HashSet<>() ;

    @Id
    @GeneratedValue(generator = "dno")
    @GenericGenerator(name="dno",strategy = "assigned")
    public Integer getDeptno() {
        return deptno;
    }

    public void setDeptno(Integer deptno) {
        this.deptno = deptno;
    }

    public String getDname() {
        return dname;
    }

    public void setDname(String dname) {
        this.dname = dname;
    }

    public String getLoc() {
        return loc;
    }

    public void setLoc(String loc) {
        this.loc = loc;
    }

    @OneToMany(cascade = CascadeType.ALL,fetch = FetchType.LAZY)
    @JoinColumn(name = "deptno",updatable = false)
    public Set<Emp> getEmps() {
        return emps;
    }

    public void setEmps(Set<Emp> emps) {
        this.emps = emps;
    }
}

Emp.java

package com.itcloud.pojo;

import org.hibernate.annotations.GenericGenerator;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="emp")
public class Emp {

    private Integer empno ;
    private String ename ;
    private String job ;

    public Emp() {
    }

    public Emp(Integer empno, String ename, String job) {
        this.empno = empno;
        this.ename = ename;
        this.job = job;
    }

    @Id
    @GeneratedValue(generator = "eno")
    @GenericGenerator(name = "eno",strategy = "assigned")
    public Integer getEmpno() {
        return empno;
    }

    public void setEmpno(Integer empno) {
        this.empno = empno;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }
}

測試用例：

 @Test
    public void post(){
        Dept dept = new Dept() ;
        dept.setDeptno(11);
        dept.setDname("開發部門");
        dept.setLoc("403");

        Emp emp1 = new Emp(7777,"smith","java開發") ;
        Emp emp2 = new Emp(7778,"jack","後端開發") ;

        dept.getEmps().add(emp1) ;
        dept.getEmps().add(emp2) ;

        session.save(emp1) ;
        session.save(emp2) ;
        session.save(dept) ;


    }

***********1-N（N-1）雙向外鍵關聯

package com.itcloud.pojo;

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

@Entity
public class Dept {
    private int deptno;
    private String dname;
    private String loc;
    private Set<Emp> emps = new HashSet<>();

    @Id
    @Column(name = "deptno", nullable = false)
    public int getDeptno() {
        return deptno;
    }

    public void setDeptno(int deptno) {
        this.deptno = deptno;
    }

    @Basic
    @Column(name = "dname", nullable = true, length = 255)
    public String getDname() {
        return dname;
    }

    public void setDname(String dname) {
        this.dname = dname;
    }

    @Basic
    @Column(name = "loc", nullable = true, length = 255)
    public String getLoc() {
        return loc;
    }

    public void setLoc(String loc) {
        this.loc = loc;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Dept dept = (Dept) o;

        if (deptno != dept.deptno) return false;
        if (dname != null ? !dname.equals(dept.dname) : dept.dname != null) return false;
        if (loc != null ? !loc.equals(dept.loc) : dept.loc != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = deptno;
        result = 31 * result + (dname != null ? dname.hashCode() : 0);
        result = 31 * result + (loc != null ? loc.hashCode() : 0);
        return result;
    }

    @OneToMany(cascade = CascadeType.ALL,fetch = FetchType.LAZY)
    @JoinColumn(name="deptno")
    public Set<Emp> getEmps() {
        return emps;
    }

    public void setEmps(Set<Emp> emps) {
        this.emps = emps;
    }
}

package com.itcloud.pojo;

import javax.persistence.*;

@Entity
public class Emp {
    private int empno;
    private String ename;
    private String job;
    private Dept dept;

    public Emp(int empno, String ename, String job) {
        this.empno = empno;
        this.ename = ename;
        this.job = job;
    }

    @Id
    @Column(name = "empno", nullable = false)
    public int getEmpno() {
        return empno;
    }

    public void setEmpno(int empno) {
        this.empno = empno;
    }

    @Basic
    @Column(name = "ename", nullable = true, length = 255)
    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    @Basic
    @Column(name = "job", nullable = true, length = 255)
    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Emp emp = (Emp) o;

        if (empno != emp.empno) return false;
        if (ename != null ? !ename.equals(emp.ename) : emp.ename != null) return false;
        if (job != null ? !job.equals(emp.job) : emp.job != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = empno;
        result = 31 * result + (ename != null ? ename.hashCode() : 0);
        result = 31 * result + (job != null ? job.hashCode() : 0);
        return result;
    }

    @ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.EAGER)
    @JoinColumn(name = "deptno", referencedColumnName = "deptno")
    public Dept getDept() {
        return dept;
    }

    public void setDept(Dept dept) {
        this.dept = dept;
    }
}

注意點：

　　1.不管是在多方仍是在一方，都要加上：@JoinColumn(name="deptno")這一語句，若是不加則沒法級聯，deptno爲多方的外鍵，

　　2.不要加mappedBy這一屬性，由於加上這一屬性只能夠從多方進行級聯，而一方沒法進行級聯，就須要設置①，②兩個字段

測試：

 @Test
    public void post(){
        Dept dept = new Dept() ;
        dept.setDeptno(11);
        dept.setDname("開發部門");
        dept.setLoc("313");

        Emp emp1 = new Emp(7777,"smith","java開發") ;
        Emp emp2 = new Emp(7778,"jack","後端開發") ;

        dept.getEmps().add(emp1) ;
        dept.getEmps().add(emp2) ;
//        emp1.setDept(dept);//②
//        emp2.setDept(dept);//①
        session.save(emp1) ;
        session.save(emp2) ;
        session.save(dept) ;

    }

結果

Hibernate: 
    insert 
    into
        Emp
        (deptno, ename, job, empno) 
    values
        (?, ?, ?, ?)
Hibernate: 
    insert 
    into
        Emp
        (deptno, ename, job, empno) 
    values
        (?, ?, ?, ?)
Hibernate: 
    insert 
    into
        Dept
        (dname, loc, deptno) 
    values
        (?, ?, ?)
Hibernate: 
    update
        Emp 
    set
        deptno=? 
    where
        empno=?
Hibernate: 
    update
        Emp 
    set
        deptno=? 
    where
        empno=?

************多對多外鍵關聯

表結構：

CREATE TABLE `teachers` (
  `tid` int(11) NOT NULL,
  `tname` varchar(255) NOT NULL DEFAULT '',
  PRIMARY KEY (`tid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


CREATE TABLE `students` (
  `sid` int(11) NOT NULL,
  `sname` varchar(15) NOT NULL DEFAULT '',
  PRIMARY KEY (`sid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


-- 中間關係維護表
CREATE TABLE `stu_teach` (
  `tid` int(11) NOT NULL,
  `sid` int(11) NOT NULL,
  KEY `FKt56181amkhrdpmd2ici8ngp35` (`sid`),
  KEY `FKe9ifjo0m9y756vlrgmb8oygsa` (`tid`),
  CONSTRAINT `FKe9ifjo0m9y756vlrgmb8oygsa` FOREIGN KEY (`tid`) REFERENCES `teachers` (`tid`),
  CONSTRAINT `FKt56181amkhrdpmd2ici8ngp35` FOREIGN KEY (`sid`) REFERENCES `students` (`sid`),-- 這裏面的外鍵是開發工具加的,不知道爲啥mmp
  CONSTRAINT `fk_sid` FOREIGN KEY (`sid`) REFERENCES `students` (`sid`) ON DELETE NO ACTION ON UPDATE CASCADE,
  CONSTRAINT `fk_tid` FOREIGN KEY (`tid`) REFERENCES `teachers` (`tid`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

@ManyToMany
    @JoinTable(
            name = "stu_teach",
            joinColumns = {@JoinColumn(name = "tid",updatable = false)},
            inverseJoinColumns = {@JoinColumn(name="sid",updatable = false)}
    )
    public Set<Students> getStus() {
        return stus;
    }

在Teachers.java類中上面的註解便可知足單向多對多開發；

***********雙向多對多

Students.java

    private Set<Teachers> teachers = new HashSet<>() ;
    @ManyToMany(cascade = CascadeType.ALL,fetch = FetchType.LAZY)
    @JoinTable(
            name = "stu_teach",
            joinColumns = {@JoinColumn(name = "sid",updatable = false)},//該實體對應表的主鍵
            inverseJoinColumns = {@JoinColumn(name="tid",updatable = false)}
    )
    public Set<Teachers> getTeachers() {
        return teachers;
    }

Teacher.java

 private Set<Students> stus = new HashSet<>();
    @ManyToMany(cascade = CascadeType.MERGE,fetch = FetchType.LAZY)
    @JoinTable(
            name = "stu_teach",
            joinColumns = {@JoinColumn(name = "tid",updatable = false)},//該實體對應表的主鍵
            inverseJoinColumns = {@JoinColumn(name="sid",updatable = false)}
    )
    public Set<Students> getStus() {
        return stus;
    }