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hibernate inverse=true
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1，部门与员工是一对多，
部门或员工任何一方去维护他们的映射关系都可以，在关系表中都可以互相找到，可是在对象关系中，双方都要去维护，
如emp.setDepart(depart);depart.setEmps(emps);
这样hibernate会产生重复的更新语句，效率低，为了让对象之间的关系都维护好，而sql语句有没有多余，
通常让一的那一方不去维护之间的关联关系，就是用inverse=true;
解释为是否放弃维护关系--是，我的理解是：是否让对方去维护--是，因为inverse是倒转的，相反的意思
Department.java，
package com.maple.hibernate.domain;import java.util.List;import java.util.Map;import java.util.Set;public class Department { private int id; private String name; private Set<Employee> emps; //private Map<String,Employee> emps; /*private List<Employee> emps;*/ public Set<Employee> getEmps() { return emps; } public void setEmps(Set<Employee> emps) { this.emps = emps; } /*public Map<String, Employee> getEmps() { return emps; } public void setEmps(Map<String, Employee> emps) { this.emps = emps; }*/ /*public List<Employee> getEmps() { return emps; } public void setEmps(List<Employee> emps) { this.emps = emps; }*/ 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; } }
Employee.java
package com.maple.hibernate.domain;public class Employee { private int id; private String name; private Department depart; public Department getDepart() { return depart; } public void setDepart(Department depart) { this.depart = depart; } @Override public String toString() { return "Employee [id=" + id + ", name=" + name + "]"; } //private Department depart; 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 getDepart() { return depart; } public void setDepart(Department depart) { this.depart = depart; }*/ }
Department.hbm.xml
<?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="com.maple.hibernate.domain"> <class name="Department"> <id name="id"> <generator class="native" /> </id> <property name="name" /> <set name="emps" inverse="true"> <key column="depart_id"/> <one-to-many class="Employee"/> </set> <!-- <list name="emps"> <key column="depart_id"/> <list-index column="order_col"/> <one-to-many class="Employee"/> </list> --> <!-- <bag name="emps"> <key column="depart_id"/> <one-to-many class="Employee"/> </bag> --> <!-- <map name="emps"> <key column="depart_id"/> <map-key type="string" column="name"/> <one-to-many class="Employee"/> </map> --> </class></hibernate-mapping>
Employee.hbm.xml
<?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="com.maple.hibernate.domain"> <class name="Employee"> <id name="id"> <generator class="native" /> </id> <property name="name" unique="true"/> <many-to-one name="depart" column="depart_id"/> </class></hibernate-mapping>
测试
public class Many2One { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub add(); queryDepart(1); //System.out.println("ff"); //Employee emp=query(1); //System.out.println("ffff depart name:"+emp.getDepart().getName()); }
static Department add(){ Session s=null; Transaction tx=null; try{ s=HibernateUtil.getSession(); /*List<Employee> emps=new ArrayList<Employee>();*/ //Map<String,Employee> emps=new HashMap<String,Employee>(); Set<Employee> emps=new HashSet<Employee>(); Department depart=new Department(); depart.setName("software"); Employee emp=new Employee(); emp.setDepart(depart); //导致更新语句 emp.setName("aaa"); Employee emp1=new Employee(); emp1.setDepart(depart); //导致更新语句 emp1.setName("aaa1"); /*emps.put(emp1.getName(), emp1); emps.put(emp.getName(), emp); */ emps.add(emp); emps.add(emp1); depart.setEmps(emps); //导致对employee表中depart_id的更新语句 tx=s.beginTransaction(); s.save(depart); //如果放下面，employee会多出一条更新语句 s.save(emp); //如果设置了not-null=true，则出错 s.save(emp1); tx.commit(); System.out.println(depart.getEmps().getClass()); //HashSet hs=(HashSet) depart.getEmps();//类转换异常 return depart; }finally{ if(s!=null){ s.close(); } } }
static Department queryDepart(int departid){ Session s=null; try{ s=HibernateUtil.getSession(); Department depart=(Department) s.get(Department.class, departid); System.out.println("emps:"+depart.getEmps()); return depart; }finally{ if(s!=null){ s.close(); } } }
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hibernate inverse=true
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