Hibernate之JPA的关联映射
JPA的关联映射：
1.导包，位于hibernate-lib-jpa里面的包；
删除对Java EE 5 Libraries的使用。
2.书写实体类，书写注释。注意注释是导的javax.类;
@id
@GeneratedValue 为主键生成策略（默认为native）;
View Code
1 import javax.persistence.Entity; 2 import javax.persistence.GeneratedValue; 3 import javax.persistence.Id; 4 import javax.persistence.Table; 5 6 7 @Entity 8 @Table(name="a_user") 9 public class User { 10 private int id; 11 private String name; 12 private int age; 13 14 @Id 15 @GeneratedValue 16 public int getId() { 17 return id; 18 } 19 public void setId(int id) { 20 this.id = id; 21 }
3.hibernate.cfg.xml中配置实体类，<mapping class="com.kebin.pojo.User" />
hibernate.cfg.xml
1 <!DOCTYPE hibernate-configuration PUBLIC 2 "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> 4 5 <hibernate-configuration> 6 <session-factory name="foo"> 7 <property name="show_sql">true</property> 8 <property name="myeclipse.connection.profile">MYSQL</property> 9 <property name="connection.url"> 10 jdbc:mysql://127.0.0.1:3306/mysql 11 </property> 12 <property name="connection.username">root</property> 13 <property name="connection.password">root</property> 14 <property name="connection.driver_class"> 15 com.mysql.jdbc.Driver 16 </property> 17 <property name="dialect"> 18 org.hibernate.dialect.MySQL5Dialect 19 </property> 20 <property name="format_sql">true</property> 21 <property name="hbm2ddl.auto">update</property> 22 <mapping class="com.kebin.pojo.User" /> 23 24 </session-factory> 25 </hibernate-configuration>
4.书写方法，创建表格；简单的配置就完成了，直接运行。
Userutil
1 package com.kebin.util; 2 3 import org.hibernate.cfg.AnnotationConfiguration; 4 import org.hibernate.cfg.Configuration; 5 import org.hibernate.tool.hbm2ddl.SchemaExport; 6 7 public class Userutil { 8 9 public static void main(String[] args) { 10 Configuration cfg = new AnnotationConfiguration().configure(); 11 SchemaExport se = new SchemaExport(cfg); 12 se.create(true, true); 13 14 } 15 16 }
一、多对一关联映射
项目一般都用双向配置，所以以下只给出双向的。
1.书写两个类，然后再hibernate.cfg.xml中配置实体类。
2. 多的一端维护:@ManyToOne； 添加一个外键。
@JoinColumn(name="cid") ； cid根据注释代码get方法的类取名。
3.少的一端：@OneToMany(mappedBy="classes");
mappedBy方法只管加载数据，外键关系交给""处理。
4.hibernate.cfg.xml中配置： <mapping class="com.kebin.pojo.Class" />
<mapping class="com.kebin.pojo.Student" />
Student.java
1 @Entity 2 @Table(name="t_student") 3 public class Student { 4 private int id; 5 private String name; 6 private Class classes; 7 8 9 @Id 10 @GeneratedValue 11 public int getId() { 12 return id; 13 } 14 public void setId(int id) { 15 this.id = id; 16 } 17 public String getName() { 18 return name; 19 } 20 public void setName(String name) { 21 this.name = name; 22 } 23 @ManyToOne 24 @JoinColumn(name="cid") 25 public Class getClasses() { 26 return classes; 27 } 28 public void setClasses(Class classes) { 29 this.classes = classes; 30 }
Class.java
1 @Entity 2 @Table(name="t_class") 3 public class Class { 4 private int id; 5 private String name; 6 private Set<Student> students = new HashSet<Student>(); 7 8 @Id 9 @GeneratedValue 10 public int getId() { 11 return id; 12 } 13 public void setId(int id) { 14 this.id = id; 15 } 16 public String getName() { 17 return name; 18 } 19 public void setName(String name) { 20 this.name = name; 21 } 22 @OneToMany(mappedBy="classes") 23 public Set<Student> getStudents() { 24 return students; 25 } 26 public void setStudents(Set<Student> students) { 27 this.students = students; 28 }
一、一对一关联映射
用得比较少，一般直接把多对一关系的外键设置唯一属性即可；
1.一端：@ManyToOne；
@JoinColumn(name="cid",unique=true) ；
2.另一端：@OneToOne(mappedBy="wife")；代码如下
Husband.java
1 @Entity 2 @Table(name="t_husband") 3 public class Husband { 4 private int id; 5 private String name; 6 private Wife wife; 7 @Id 8 @GeneratedValue 9 public int getId() { 10 return id; 11 } 12 public void setId(int id) { 13 this.id = id; 14 } 15 public String getName() { 16 return name; 17 } 18 public void setName(String name) { 19 this.name = name; 20 } 21 @ManyToOne 22 @JoinColumn(name="wid",unique=true) 23 public Wife getWife() { 24 return wife; 25 } 26 public void setWife(Wife wife) { 27 this.wife = wife; 28 } 29
Wife.java
1 @Entity 2 @Table(name="t_wife") 3 public class Wife { 4 private int id; 5 private String name; 6 private Husband husband; 7 8 9 @Id 10 @GeneratedValue 11 public int getId() { 12 return id; 13 } 14 public void setId(int id) { 15 this.id = id; 16 } 17 public String getName() { 18 return name; 19 } 20 public void setName(String name) { 21 this.name = name; 22 } 23 @OneToOne(mappedBy="wife") 24 public Husband getHusband() { 25 return husband; 26 } 27 public void setHusband(Husband husband) { 28 this.husband = husband; 29 }
一、一对多关联映射
这个就不介绍了，和多对一差不多。
一、多对多关联映射
1.一端：@ManyToMany
@JoinTable(name="t_teacher_class",joinColumns={@JoinColumn(name="tid")}, inverseJoinColumns={@JoinColumn(name="cid")})
2.另一端：@ManyToMany(mappedBy="classes")
Teacher.java
1 @Entity 2 @Table(name="t_teacher") 3 public class Teacher { 4 private int id; 5 private String name; 6 private Set<Class> classes = new HashSet<Class>(); 7 8 @Id 9 @GeneratedValue 10 public int getId() { 11 return id; 12 } 13 public void setId(int id) { 14 this.id = id; 15 } 16 public String getName() { 17 return name; 18 } 19 public void setName(String name) { 20 this.name = name; 21 } 22 @ManyToMany 23 @JoinTable(name="t_teacher_class",joinColumns={@JoinColumn(name="tid")}, 24 inverseJoinColumns={@JoinColumn(name="cid")}) 25 public Set<Class> getClasses() { 26 return classes; 27 } 28 public void setClasses(Set<Class> classes) { 29 this.classes = classes; 30 }
Class.java
1 @Entity 2 @Table(name="t_class") 3 public class Class { 4 private int id; 5 private String name; 6 private Set<Teacher> teachers = new HashSet<Teacher>(); 7 8 @Id 9 @GeneratedValue 10 public int getId() { 11 return id; 12 } 13 public void setId(int id) { 14 this.id = id; 15 } 16 public String getName() { 17 return name; 18 } 19 public void setName(String name) { 20 this.name = name; 21 } 22 23 @ManyToMany(mappedBy="classes") 24 public Set<Teacher> getTeachers() { 25 return teachers; 26 } 27 public void setTeachers(Set<Teacher> teachers) { 28 this.teachers = teachers; 29 } 30