十二 集合映射之Map集合
十二 Map集合映射Map是以键值对的形式存放数据的 现在我们假设员工数据的name为唯一的 现在我们来看映射文件<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="vo.util.bean"><class name="Employee"><id name="id"><generator unique="true"/><many-to-one name="derpartment" column="depaer_id" not-null="true"/></class></hibernate-mapping>unique是定义其为唯一键的约束 员工实体类package vo.util.bean;/** * 员工类 * @author Administrator * */public class Employee { private int id; private String name; private Department derpartment;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Department getDerpartment() {return derpartment;}public void setDerpartment(Department derpartment) {this.derpartment = derpartment;}@Overridepublic String toString() {// TODO Auto-generated method stubreturn "id="+this.id+" name="+this.name;}}现在我们来定义部门实体package vo.util.bean;import java.util.Map;/** * 部门类 * @author Administrator * */public class Department { private int id; private String name; private Map<String,Employee> ems; public Map<String, Employee> getEms() {return ems;}public void setEms(Map<String, Employee> ems) {this.ems = ems;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}}这行是定义Map集合的 private Map<String,Employee> ems;映射文件 <?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><hibernate-mapping package="vo.util.bean"><class name="Department"><id name="id"><generator /></set> --> <map name="ems"> <key column="depaer_id"/> <map-key type="string" column="name"/> <one-to-many class="Employee"/> </map></class></hibernate-mapping>分析 发现这跟List并没有太大的区别 其实map节点的里面字段属性意义都是一样的就<map-key 这个节点有特殊之处 这是指定其键的 因为Map是以键值对的形式存在的 type是指定键的类型 当前指定为string类型 这个column是干什么用的呢？这个是指定其键的值是以那个列为键的 当前是以员工的name这个列作为键存在的 测试类package vo.util.test;import java.util.HashMap;import java.util.HashSet;import java.util.Map;import org.hibernate.Session;import org.hibernate.Transaction;import vo.util.HibernateUtil;import vo.util.bean.Department;import vo.util.bean.Employee;public class OneToMany {/** * @param args */public static void main(String[] args) { add(); query(1);} static Department add(){ Session session = null; Transaction tx = null; try{ session =HibernateUtil.getSession(); tx = session.beginTransaction(); //…你的代码save,delete,update,get… Department dpart=new Department(); dpart.setName("政企事业部"); Employee em1=new Employee(); em1.setName("员工李小仙"); em1.setDerpartment(dpart); Employee em2=new Employee(); em2.setName("员工张小三"); em2.setDerpartment(dpart); Map<String,Employee> ems=new HashMap<String, Employee>(); ems.put(em1.getName(), em1); ems.put(em2.getName(), em2); dpart.setEms(ems); session.save(dpart); session.save(em1); session.save(em2); tx.commit(); return dpart; }finally{ if(session != null)session.close(); } } static Department query(int id){ Session session=null; try{ session=HibernateUtil.getSession(); Department d=(Department)session.get(Department.class, id); System.out.println(d.getEms()); return d; }finally{ if(session != null)session.close(); } }}通过输出发现：输出是键值对的形式输出的 end 完毕！?