Hibernate中用注解配置一对多双向关联和多对一单向关联

2023-01-11 08:01:56

Hibernate中用注解配置一对多双向关联和多对一单向关联

Hibernate提供了Hibernate Annotations扩展包，使用注解完成映射。在Hibernate3.3之前，需单独下载注解开发包

配置持久化类

配置关联关系

下面我们先从多对一单向关联关系讲起，多对一单向关联就是在多的一方植入一的一方的主键作为外键，下面我们先进行初始配置，

在配置的过程中我们会遇到一个问题就是无论用load还是get都不会出现延迟加载，那么我们应该如何设置为要延迟加载，这样做的好处是可以在用的时候才加载对应的信息，节约内存

hibernate中，延迟加载大致可以分为两类，一类是延迟属性加载，另一类是延迟关联实体加载。

普通属性：分两种情况，一种是集合属性，一种是非集合属性（如String、Integer......）

集合属性的延迟加载通过PersistentSet、 PersistentList、PersistentBag、PersistentMap、PersistentSortedMap、 PersistentSortedSet作为代理类来实现，代理类中保存了session以及owner属性，owner属性表示了集合属性所属的one 侧的实体。

非集合类属性的延迟加载相对比较复杂。仅通过@Basic(fetch = FetchType.LAZY)注解是无法实现延迟加载的。需要让实体实现FieldHandled接口，声明FieldHandler属性，通过拦截器原理注入对应的FieldHandler属性，起到类似于上述代理类的作用，FieldHandler同样也保持了session，以及需要延迟加载的属性。

我们发现对非集合属性即时设置了@Basic(fetch = FetchType.LAZY)仍无法实现延迟加载，可以看生成的sql语句

接下来我们会对一对多单向关联进行测试，验证对集合类属性，是否可以起到延迟加载的功能

注意：不可以对有关联关系的属性设置@Transient

配置多对一的单向关联关系示例

 package cn.happy.entity;

 import javax.persistence.Basic;

 import javax.persistence.Column;

 import javax.persistence.Entity;

 import javax.persistence.FetchType;

 import javax.persistence.GeneratedValue;

 import javax.persistence.GenerationType;

 import javax.persistence.Id;

 import javax.persistence.JoinColumn;

 import javax.persistence.ManyToOne;

 import javax.persistence.SequenceGenerator;

 import javax.persistence.Table;

 import javax.persistence.Transient;

 @Entity

 @Table(name = "EMP")

 public class Emp {

     @Id

     @Column(name = "EMPNO")

     @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "emp_num")

     @SequenceGenerator(name = "emp_num", sequenceName = "emp_num_id", allocationSize = , initialValue = )

     private Integer empNo;

     @Column(name = "EMPNAME")

     private String empName;

     @ManyToOne()

     @JoinColumn(name = "DEPTNO")

     /*@Basic(fetch=FetchType.LAZY)*/

     private Dept dept;

     public Emp() {

         super();

     }

     public Emp(Integer empNo, String empName) {

         super();

         this.empNo = empNo;

         this.empName = empName;

     }

     public Integer getEmpNo() {

         return empNo;

     }

     public void setEmpNo(Integer empNo) {

         this.empNo = empNo;

     }

     public String getEmpName() {

         return empName;

     }

     public void setEmpName(String empName) {

         this.empName = empName;

     }

     public Dept getDept() {

         return dept;

     }

     public void setDept(Dept dept) {

         this.dept = dept;

     }

 }

 package cn.happy.entity;

 import java.util.HashSet;

 import java.util.Set;

 import javax.persistence.CascadeType;

 import javax.persistence.Column;

 import javax.persistence.Entity;

 import javax.persistence.GeneratedValue;

 import javax.persistence.GenerationType;

 import javax.persistence.Id;

 import javax.persistence.JoinColumn;

 import javax.persistence.OneToMany;

 import javax.persistence.SequenceGenerator;

 import javax.persistence.Table;

 import javax.persistence.Transient;

 import org.hibernate.annotations.Cascade;

 @Entity

 @Table(name = "DEPT")

 public class Dept {

     @Id

     @Column(name = "DEPTNO")

     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="dept_num")

     @SequenceGenerator(name="dept_num",sequenceName="dept_num_no",allocationSize=1,initialValue=1)

     private Integer deptNo;

     @Column(name = "DEPTNAME")

     private String deptName;

     public Integer getDeptNo() {

         return deptNo;

     }

     public void setDeptNo(Integer deptNo) {

         this.deptNo = deptNo;

     }

     public String getDeptName() {

         return deptName;

     }

     public void setDeptName(String deptName) {

         this.deptName = deptName;

     }

 }

 /**

      * 注解测试多对一映射   员工表（多）对应部门表（一）的映射,即只在员工表中植入部门表的信息

      * */

     @Test

     public void manytooneSingle(){

         /**

          * 查询操作

          * **/

         /*SessionFactory sf=new AnnotationConfiguration().configure().buildSessionFactory();

         Session session = sf.openSession();

         Emp emp=(Emp)session.load(Emp.class, 4);

         System.out.println(emp.getEmpName()+"\t"+emp.getDept().getDeptName());*/

         /**

          * 添加操作

          * **/

         SessionFactory sf=new AnnotationConfiguration().configure().buildSessionFactory();

         Session session = sf.openSession();

         Transaction tx = session.beginTransaction();

         Dept dept = (Dept)session.load(Dept.class, 3);

         Emp emp=new Emp();

         emp.setEmpName("户梦艳");

         emp.setEmpNo(001);

         emp.setDept(dept);

         Emp emp2=new Emp();

         emp2.setEmpName("户梦艳2");

         emp2.setEmpNo(002);

         emp2.setDept(dept);

         session.save(emp);

         session.save(emp2);

         tx.commit();

         session.close();

     }

一对多双单向配置

 package cn.happy.entity;

 import java.util.HashSet;

 import java.util.Set;

 import javax.persistence.CascadeType;

 import javax.persistence.Column;

 import javax.persistence.Entity;

 import javax.persistence.GeneratedValue;

 import javax.persistence.GenerationType;

 import javax.persistence.Id;

 import javax.persistence.JoinColumn;

 import javax.persistence.OneToMany;

 import javax.persistence.SequenceGenerator;

 import javax.persistence.Table;

 import javax.persistence.Transient;

 @Entity

 @Table(name="Dept")

 public class Dept {

     @Id

     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="dept_num")

     @SequenceGenerator(name="dept_num",sequenceName="dept_num_no",allocationSize=,initialValue=)

     private Integer deptNo;

     @Column

     private String deptName;

     @OneToMany(cascade={CascadeType.ALL})

     @JoinColumn(name="deptno")

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

     public Set<Emp> getEmps() {

         return emps;

     }

     public void setEmps(Set<Emp> emps) {

         this.emps = emps;

     }

     public Integer getDeptNo() {

         return deptNo;

     }

     public void setDeptNo(Integer deptNo) {

         this.deptNo = deptNo;

     }

     public String getDeptName() {

         return deptName;

     }

     public void setDeptName(String deptName) {

         this.deptName = deptName;

     }

 }

 package cn.happy.entity;

 import javax.persistence.Basic;

 import javax.persistence.Column;

 import javax.persistence.Entity;

 import javax.persistence.FetchType;

 import javax.persistence.GeneratedValue;

 import javax.persistence.GenerationType;

 import javax.persistence.Id;

 import javax.persistence.JoinColumn;

 import javax.persistence.ManyToOne;

 import javax.persistence.SequenceGenerator;

 import javax.persistence.Table;

 import javax.persistence.Transient;

 import org.hibernate.bytecode.javassist.FieldHandled;

 import org.hibernate.bytecode.javassist.FieldHandler;

 @Entity

 @Table(name = "EMP")

 public class Emp {

     @Id

     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="emp_num")

     @SequenceGenerator(name="emp_num",sequenceName="emp_num_no",allocationSize=,initialValue=)

     private Integer empNo;

     @Column

     private String empName;

 //    @ManyToOne

 //    @JoinColumn(name="deptno")

 //    @Basic(fetch=FetchType.LAZY)

 //    private Dept dept;

 //

 //    public Dept getDept() {

 //        return dept;

 //    }

 //

 //    public void setDept(Dept dept) {

 //        this.dept = dept;

 //    }

     public Emp() {

         super();

     }

     public Emp(Integer empNo, String empName) {

         super();

         this.empNo = empNo;

         this.empName = empName;

     }

     public Integer getEmpNo() {

         return empNo;

     }

     public void setEmpNo(Integer empNo) {

         this.empNo = empNo;

     }

     public String getEmpName() {

         return empName;

     }

     public void setEmpName(String empName) {

         this.empName = empName;

     }

 }

 /**

      * 测试一对多单向添加操作

      * */

     @Test

     public void insertOneToManySingle(){

         Emp emp=new Emp();

         emp.setEmpName("*");

         Emp emp2=new Emp();

         emp2.setEmpName("王想想");

         Dept dept=new Dept();

         dept.setDeptName("教务部");

         //设置级联操作

         dept.getEmps().add(emp);

         dept.getEmps().add(emp2);

         session.save(dept);

         tx.commit();

         System.out.println("insert ok");

     }

     /**

      * 测试一对多单向查询操作

      * */

     @Test

     public void selectOneToManySingle(){

         Dept dept = (Dept)session.load(Dept.class, );

         System.out.println("======================");

         System.out.println("部门名称:"+dept.getDeptName());

         System.out.println("=======================");

         //体现了延迟加载

         for (Emp emp : dept.getEmps()) {

             System.out.println("雇员名称："+emp.getEmpName());

         }

         //Emp emp = (Emp)session.load(Emp.class, 1);

     }

一对多双向配置

 package cn.happy.entity;

 import java.util.HashSet;

 import java.util.Set;

 import javax.persistence.CascadeType;

 import javax.persistence.Column;

 import javax.persistence.Entity;

 import javax.persistence.GeneratedValue;

 import javax.persistence.GenerationType;

 import javax.persistence.Id;

 import javax.persistence.JoinColumn;

 import javax.persistence.OneToMany;

 import javax.persistence.SequenceGenerator;

 import javax.persistence.Table;

 import javax.persistence.Transient;

 @Entity

 @Table(name="Dept")

 public class Dept {

     @Id

     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="dept_num")

     @SequenceGenerator(name="dept_num",sequenceName="dept_num_no",allocationSize=,initialValue=)

     private Integer deptNo;

     @Column

     private String deptName;

     @OneToMany(mappedBy="dept",cascade={CascadeType.ALL})

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

     public Set<Emp> getEmps() {

         return emps;

     }

     public void setEmps(Set<Emp> emps) {

         this.emps = emps;

     }

     public Integer getDeptNo() {

         return deptNo;

     }

     public void setDeptNo(Integer deptNo) {

         this.deptNo = deptNo;

     }

     public String getDeptName() {

         return deptName;

     }

     public void setDeptName(String deptName) {

         this.deptName = deptName;

     }

 }

 package cn.happy.entity;

 import javax.persistence.Basic;

 import javax.persistence.Column;

 import javax.persistence.Entity;

 import javax.persistence.FetchType;

 import javax.persistence.GeneratedValue;

 import javax.persistence.GenerationType;

 import javax.persistence.Id;

 import javax.persistence.JoinColumn;

 import javax.persistence.ManyToOne;

 import javax.persistence.SequenceGenerator;

 import javax.persistence.Table;

 import javax.persistence.Transient;

 import org.hibernate.bytecode.javassist.FieldHandled;

 import org.hibernate.bytecode.javassist.FieldHandler;

 @Entity

 @Table(name = "EMP")

 public class Emp {

     @Id

     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="emp_num")

     @SequenceGenerator(name="emp_num",sequenceName="emp_num_no",allocationSize=,initialValue=)

     private Integer empNo;

     @Column

     private String empName;

     @ManyToOne

     @JoinColumn(name="deptno")

     @Basic(fetch=FetchType.LAZY)

     private Dept dept;

     public Dept getDept() {

         return dept;

     }

     public void setDept(Dept dept) {

         this.dept = dept;

     }

     public Emp() {

         super();

     }

     public Emp(Integer empNo, String empName) {

         super();

         this.empNo = empNo;

         this.empName = empName;

     }

     public Integer getEmpNo() {

         return empNo;

     }

     public void setEmpNo(Integer empNo) {

         this.empNo = empNo;

     }

     public String getEmpName() {

         return empName;

     }

     public void setEmpName(String empName) {

         this.empName = empName;

     }

 }

     /**

      * 双向一对多的添加操作

      * */

     @Test

     public void oneToManyDouble(){

         Dept dept=new Dept();

         dept.setDeptName("财务部");

         Emp emp=new Emp();

         emp.setEmpName("邹乐");

         emp.setDept(dept);

         Emp emp2=new Emp();

         emp2.setEmpName("范子阳");

         emp2.setDept(dept);

         dept.getEmps().add(emp);

         dept.getEmps().add(emp2);

         session.save(dept);

         tx.commit();

     }

 /**

      * 双向一对多的查询操作

      * */

     @Test

     public void selectOneToManyDouble(){

         Dept dept = (Dept)session.load(Dept.class, );

         System.out.println("部门名称："+dept.getDeptName());

         for (Emp emp : dept.getEmps()) {

             System.out.println("职工姓名："+emp.getEmpName());

         }

         System.out.println("==================================================");

         Emp emp = (Emp)session.load(Emp.class, );

         System.out.println("职工姓名："+emp.getEmpName()+"\t部门名称："+emp.getDept().getDeptName());

     }

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