Hibernate中用注解配置一对多双向关联和多对一单向关联-白红宇

Hibernate中用注解配置一对多双向关联和多对一单向关联

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发布时间：2019-06-12

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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

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

1 package cn.happy.entity; 2  3 import javax.persistence.Basic; 4 import javax.persistence.Column; 5 import javax.persistence.Entity; 6 import javax.persistence.FetchType; 7 import javax.persistence.GeneratedValue; 8 import javax.persistence.GenerationType; 9 import javax.persistence.Id;10 import javax.persistence.JoinColumn;11 import javax.persistence.ManyToOne;12 import javax.persistence.SequenceGenerator;13 import javax.persistence.Table;14 import javax.persistence.Transient;15 16 @Entity17 @Table(name = "EMP")18 public class Emp {19     @Id20     @Column(name = "EMPNO")21     @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "emp_num")22     @SequenceGenerator(name = "emp_num", sequenceName = "emp_num_id", allocationSize = 1, initialValue = 1)23     private Integer empNo;24 25     @Column(name = "EMPNAME")26     private String empName;27     28     @ManyToOne()29     @JoinColumn(name = "DEPTNO")30     /*@Basic(fetch=FetchType.LAZY)*/31     private Dept dept;32 33     34     public Emp() {35         super();36     }37 38     public Emp(Integer empNo, String empName) {39         super();40         this.empNo = empNo;41         this.empName = empName;42     }43 44     public Integer getEmpNo() {45         return empNo;46     }47 48     public void setEmpNo(Integer empNo) {49         this.empNo = empNo;50     }51 52     public String getEmpName() {53         return empName;54     }55 56     public void setEmpName(String empName) {57         this.empName = empName;58     }59 60     public Dept getDept() {61         return dept;62     }63 64     public void setDept(Dept dept) {65         this.dept = dept;66     }67 }

1 package cn.happy.entity; 2  3 import java.util.HashSet; 4 import java.util.Set; 5  6 import javax.persistence.CascadeType; 7 import javax.persistence.Column; 8 import javax.persistence.Entity; 9 import javax.persistence.GeneratedValue;10 import javax.persistence.GenerationType;11 import javax.persistence.Id;12 import javax.persistence.JoinColumn;13 import javax.persistence.OneToMany;14 import javax.persistence.SequenceGenerator;15 import javax.persistence.Table;16 import javax.persistence.Transient;17 18 import org.hibernate.annotations.Cascade;19 20 @Entity21 @Table(name = "DEPT")22 public class Dept {23     @Id24     @Column(name = "DEPTNO")25     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="dept_num")26     @SequenceGenerator(name="dept_num",sequenceName="dept_num_no",allocationSize=1,initialValue=1)27     private Integer deptNo;28 29     @Column(name = "DEPTNAME")30     private String deptName;31 32 33     public Integer getDeptNo() {34         return deptNo;35     }36 37     public void setDeptNo(Integer deptNo) {38         this.deptNo = deptNo;39     }40 41     public String getDeptName() {42         return deptName;43     }44 45     public void setDeptName(String deptName) {46         this.deptName = deptName;47     }48 }

1 /** 2      * 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 3      * */ 4     @Test 5     public void manytooneSingle(){ 6          7         /** 8          * 查询操作 9          * **/10         /*SessionFactory sf=new AnnotationConfiguration().configure().buildSessionFactory();11         Session session = sf.openSession();12         13         Emp emp=(Emp)session.load(Emp.class, 4);14         15         System.out.println(emp.getEmpName()+"\t"+emp.getDept().getDeptName());*/16         17         /**18          * 添加操作19          * **/20         SessionFactory sf=new AnnotationConfiguration().configure().buildSessionFactory();21         Session session = sf.openSession();22         Transaction tx = session.beginTransaction();23         Dept dept = (Dept)session.load(Dept.class, 3);24         25         Emp emp=new Emp();26         emp.setEmpName("户梦艳");27         emp.setEmpNo(001);28         emp.setDept(dept);29         30         Emp emp2=new Emp();31         emp2.setEmpName("户梦艳2");32         emp2.setEmpNo(002);33         emp2.setDept(dept);34         35         session.save(emp);36         session.save(emp2);37         tx.commit();38         session.close();39         40         41     }

一对多双单向配置

1 package cn.happy.entity; 2  3 import java.util.HashSet; 4 import java.util.Set; 5  6 import javax.persistence.CascadeType; 7 import javax.persistence.Column; 8 import javax.persistence.Entity; 9 import javax.persistence.GeneratedValue;10 import javax.persistence.GenerationType;11 import javax.persistence.Id;12 import javax.persistence.JoinColumn;13 import javax.persistence.OneToMany;14 import javax.persistence.SequenceGenerator;15 import javax.persistence.Table;16 import javax.persistence.Transient;17 18 19 @Entity20 @Table(name="Dept")21 public class Dept {22     @Id    23     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="dept_num")24     @SequenceGenerator(name="dept_num",sequenceName="dept_num_no",allocationSize=1,initialValue=1)25     private Integer deptNo;26     @Column27     private String deptName;28     29     30     @OneToMany(cascade={CascadeType.ALL})31     @JoinColumn(name="deptno")32     private Set
     
       emps=new HashSet
      
       ();33 34     public Set
       
         getEmps() {35         return emps;36     }37 38     public void setEmps(Set
        
          emps) {39         this.emps = emps;40     }41 42     public Integer getDeptNo() {43         return deptNo;44     }45 46     public void setDeptNo(Integer deptNo) {47         this.deptNo = deptNo;48     }49 50     public String getDeptName() {51         return deptName;52     }53 54     public void setDeptName(String deptName) {55         this.deptName = deptName;56     }57 }

1 package cn.happy.entity; 2  3 import javax.persistence.Basic; 4 import javax.persistence.Column; 5 import javax.persistence.Entity; 6 import javax.persistence.FetchType; 7 import javax.persistence.GeneratedValue; 8 import javax.persistence.GenerationType; 9 import javax.persistence.Id;10 import javax.persistence.JoinColumn;11 import javax.persistence.ManyToOne;12 import javax.persistence.SequenceGenerator;13 import javax.persistence.Table;14 import javax.persistence.Transient;15 16 import org.hibernate.bytecode.javassist.FieldHandled;17 import org.hibernate.bytecode.javassist.FieldHandler;18 19 20 @Entity21 @Table(name = "EMP")22 public class Emp {23     24     25     26     @Id27     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="emp_num")28     @SequenceGenerator(name="emp_num",sequenceName="emp_num_no",allocationSize=1,initialValue=9)29     private Integer empNo;30 31     @Column32     private String empName;33     34    35 //    @ManyToOne36 //    @JoinColumn(name="deptno")37 //    @Basic(fetch=FetchType.LAZY)38 //    private Dept dept;39 //    40 //    public Dept getDept() {41 //        return dept;42 //    }43 //44 //    public void setDept(Dept dept) {45 //        this.dept = dept;46 //    }47 48     public Emp() {49         super();50     }51 52     public Emp(Integer empNo, String empName) {53         super();54         this.empNo = empNo;55         this.empName = empName;56     }57 58     public Integer getEmpNo() {59         return empNo;60     }61 62     public void setEmpNo(Integer empNo) {63         this.empNo = empNo;64     }65 66     public String getEmpName() {67         return empName;68     }69 70     public void setEmpName(String empName) {71         this.empName = empName;72     }73     74 75 }

1 /** 2      * 测试一对多单向添加操作 3      * */ 4     @Test 5     public void insertOneToManySingle(){ 6         Emp emp=new Emp(); 7         emp.setEmpName("李小鹏"); 8          9         Emp emp2=new Emp();10         emp2.setEmpName("王想想");11         12         Dept dept=new Dept();13         dept.setDeptName("教务部");14         //设置级联操作15         dept.getEmps().add(emp);16         dept.getEmps().add(emp2);17         18         session.save(dept);19         tx.commit();20         System.out.println("insert ok");21         22     }

1     /** 2      * 测试一对多单向查询操作 3      * */ 4     @Test 5     public void selectOneToManySingle(){ 6         Dept dept = (Dept)session.load(Dept.class, 1); 7         System.out.println("======================"); 8         System.out.println("部门名称:"+dept.getDeptName()); 9         System.out.println("=======================");10         //体现了延迟加载11         for (Emp emp : dept.getEmps()) {12             System.out.println("雇员名称："+emp.getEmpName());13         }14         //Emp emp = (Emp)session.load(Emp.class, 1);15         16         17     }

一对多双向配置

1 package cn.happy.entity; 2  3 import java.util.HashSet; 4 import java.util.Set; 5  6 import javax.persistence.CascadeType; 7 import javax.persistence.Column; 8 import javax.persistence.Entity; 9 import javax.persistence.GeneratedValue;10 import javax.persistence.GenerationType;11 import javax.persistence.Id;12 import javax.persistence.JoinColumn;13 import javax.persistence.OneToMany;14 import javax.persistence.SequenceGenerator;15 import javax.persistence.Table;16 import javax.persistence.Transient;17 18 19 @Entity20 @Table(name="Dept")21 public class Dept {22     @Id    23     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="dept_num")24     @SequenceGenerator(name="dept_num",sequenceName="dept_num_no",allocationSize=1,initialValue=1)25     private Integer deptNo;26     @Column27     private String deptName;28     29     30     @OneToMany(mappedBy="dept",cascade={CascadeType.ALL})31    32     private Set
     
       emps=new HashSet
      
       ();33 34     public Set
       
         getEmps() {35         return emps;36     }37 38     public void setEmps(Set
        
          emps) {39         this.emps = emps;40     }41 42     public Integer getDeptNo() {43         return deptNo;44     }45 46     public void setDeptNo(Integer deptNo) {47         this.deptNo = deptNo;48     }49 50     public String getDeptName() {51         return deptName;52     }53 54     public void setDeptName(String deptName) {55         this.deptName = deptName;56     }57 }

1 package cn.happy.entity; 2  3 import javax.persistence.Basic; 4 import javax.persistence.Column; 5 import javax.persistence.Entity; 6 import javax.persistence.FetchType; 7 import javax.persistence.GeneratedValue; 8 import javax.persistence.GenerationType; 9 import javax.persistence.Id;10 import javax.persistence.JoinColumn;11 import javax.persistence.ManyToOne;12 import javax.persistence.SequenceGenerator;13 import javax.persistence.Table;14 import javax.persistence.Transient;15 16 import org.hibernate.bytecode.javassist.FieldHandled;17 import org.hibernate.bytecode.javassist.FieldHandler;18 19 20 @Entity21 @Table(name = "EMP")22 public class Emp {23     24     25     26     @Id27     @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="emp_num")28     @SequenceGenerator(name="emp_num",sequenceName="emp_num_no",allocationSize=1,initialValue=9)29     private Integer empNo;30 31     @Column32     private String empName;33     34    35     @ManyToOne36     @JoinColumn(name="deptno")37     @Basic(fetch=FetchType.LAZY)38     private Dept dept;39     40     public Dept getDept() {41         return dept;42     }43 44     public void setDept(Dept dept) {45         this.dept = dept;46     }47 48     public Emp() {49         super();50     }51 52     public Emp(Integer empNo, String empName) {53         super();54         this.empNo = empNo;55         this.empName = empName;56     }57 58     public Integer getEmpNo() {59         return empNo;60     }61 62     public void setEmpNo(Integer empNo) {63         this.empNo = empNo;64     }65 66     public String getEmpName() {67         return empName;68     }69 70     public void setEmpName(String empName) {71         this.empName = empName;72     }73     74 75 }

1     /** 2      * 双向一对多的添加操作 3      * */ 4     @Test  5     public void oneToManyDouble(){ 6         Dept dept=new Dept(); 7         dept.setDeptName("财务部"); 8          9         Emp emp=new Emp();10         emp.setEmpName("邹乐");11         emp.setDept(dept);12         13         Emp emp2=new Emp();14         emp2.setEmpName("范子阳");15         emp2.setDept(dept);16         17         18         dept.getEmps().add(emp);19         dept.getEmps().add(emp2);20         21         session.save(dept);22         tx.commit();23     }24

1 /** 2      * 双向一对多的查询操作 3      * */ 4     @Test  5     public void selectOneToManyDouble(){ 6          7         Dept dept = (Dept)session.load(Dept.class, 1); 8         System.out.println("部门名称："+dept.getDeptName()); 9         for (Emp emp : dept.getEmps()) {10             System.out.println("职工姓名："+emp.getEmpName());11         }12         13         System.out.println("==================================================");14         15         Emp emp = (Emp)session.load(Emp.class, 1);16         System.out.println("职工姓名："+emp.getEmpName()+"\t部门名称："+emp.getDept().getDeptName());17     }18

转载于:https://www.cnblogs.com/hmy-1365/p/5790087.html

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