hibernate 快速入门

1.学习hibernate最重要的是关系，也就是*.hbm.xml文件的配置，不管struts，hibernate，spring还是标准的web应用，xml文件都是了解框架最直接的方法，它在某些程度上相当与注册表的功能。
2.pojo类（javabean的另一个商业名字），数据库表，他们都可以单独存在单独运行，没有问题。能够把他们有机联合起来的就是*.hbm.xml文件
3.下面来讲关系，我下面的关系都是双向的，这样好理解
3.1一对一
方式1：唯一的外键
<many-to-one unique="true"> (唯一的外键)
<one-to-one>
例子：
public class Address {
    private Long id;
    private String city;
    private Customer customer;
...set/get 方法省略

public class Customer {
    private Long id;
    private String name;
    private Address homeAddress;
...set/get 方法省略

Address.hbm.xml
<hibernate-mapping>
    <class name="com.xx.one2one.foreignkey.Address"
        table="ADDRESSES">
        <id name="id" type="long" column="ID">
            <generator class="increment" />
        </id>
        <property name="city" />
        <one-to-one name="customer"
            class="com.xx.one2one.foreignkey.Customer"/>
    </class>
</hibernate-mapping>

Customer.hbm.xml
<hibernate-mapping >
  <class name="com.xx.one2one.foreignkey.Customer">
    <id name="id" type="long" column="ID">
      <generator class="increment"/>
    </id>
    <property name="name" />
    <many-to-one name="homeAddress"
        class="com.xx.one2one.foreignkey.Address"      
        unique="true"/>       
  </class>
</hibernate-mapping>

方式2：共享主键
<one-to-one>
<one-to-one constrained="true"> (既是主键又是外键)，主键生成方式需要用：foreign
例子：
public class Person {
    private int id;
    private String name;
    private IdCard idCard = new IdCard();
...set/get 方法省略

public class IdCard {
    private int id;
    private int cardNb;
    private Person pp ;
...set/get 方法省略

IdCard.hbm.xml
<hibernate-mapping>
    <class name="com.xx.one2one.IdCard">
        <id name="id">
            <generator class="native" />
        </id>
        <property name="cardNb"></property>
        <one-to-one name="pp" class="com.xx.one2one.Person"></one-to-one>
    </class>
</hibernate-mapping>

Person.hbm.xml
<hibernate-mapping>
    <class name="com.xx.one2one.Person">
        <id name="id">
            <generator class="foreign">
                <param name="property">idCard</param>
            </generator>
        </id>
        <property name="name"></property>
        <one-to-one name="idCard" constrained="true"
            class="com.xx.one2one.IdCard">
        </one-to-one>
    </class>
</hibernate-mapping>


3.2多对一
例子：
public class Dept{
    private Integer deptno;
    private String dname;
    private String loc;
    private Set emps = new HashSet();
...set/get 方法省略

public class Emp{
    private Integer empno;
    private Dept dept=new Dept();
    private String ename;
...set/get 方法省略

dept.hbm.xml
<hibernate-mapping>
    <class name="com.xx.one2many.Dept">
        <id name="deptno">
            <column name="DEPTNO"/>
            <generator class="assigned" />
        </id>
        <property name="dname"/>
        <property name="loc"/>      
        <set name="emps" inverse="true">
            <key>
                <column name="DEPTNO"/>
            </key>
            <one-to-many class="com.xx.one2many.Emp" />
        </set>
    </class>
</hibernate-mapping>

emp.hbm.xml
<hibernate-mapping>
    <class name="com.xx.one2many.Emp">
        <id name="empno" >
            <column name="EMPNO" />
            <generator class="assigned" />
        </id>
        <many-to-one name="dept" class="com.xx.one2many.Dept"/>
        <property name="ename"/> 
    </class>
</hibernate-mapping>

3.3多对多
例子：
public class Student{   
    private String sid;
    private String sname;
    private Set<Department> departments = new HashSet<Department>(0);
...set/get 方法省略

public class Department{
    private String did;
    private String dname;
    private Set<Student> students = new HashSet<Student>(0);
...set/get 方法省略

student.hbm.xml
<hibernate-mapping package="com.xx.manytomany">
    <class name="Student" >
        <id name="sid" >
            <column name="SID" />
            <generator class="assigned" />
        </id>
        <property name="sname"/>       
        <set name="departments" table="stu_dept">
            <key>
                <column name="SID" length="10" />
            </key>
           <many-to-many class="Department" column="DID"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

department.hbm.xml
<hibernate-mapping package="com.xx.manytomany">
    <class name="Department">
        <id name="did"/>
            <generator class="assigned" />
        </id>
        <property name="dname"/>      
        <set name="students" inverse="true" table="stu_dept">
            <key>
                <column name="DID"/>
            </key>           
            <many-to-many column="SID" class="Student"></many-to-many>           
        </set>
    </class>
</hibernate-mapping>

4.你的pojo有几个属性，*.hbm.xml就几个说明项.说明项就3种类型：主键，属性，关系

5.完全理解上面的关系后在看hibernate其它部分，如果自己觉得不好理解，其实有个笨但有效的方法，那就是背下来，我对学习新技术的核心部分就采取这种方法，直接有效

6.强烈推荐看原版的hibernate-reference;hibernate in action，感觉就是不一样。