Hibernate 映射

Hibernate  的映射
 一、实体映射
	1.基本映射技术(类与表的映射,主键映射，普通字段映射) 类映射
<?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.bjsxt.po">
	<class name="Address2" table="t_address2">
		<id name="id">
			<generator class="native"></generator>
		</id>
		<property name="city"/>
		<property name="country"/>
	</class>	
</hibernate-mapping>
二、联合主键映射
<hibernate-mapping 
	package="com.bjsxt.po">
	<class name="Student" table="t_student" lazy="true" >
		<composite-id name="id" class="StudentId">
			<key-property name="firstname" type="string" column="firstname"/>
			<key-property name="lastname"/>
		</composite-id>		
		<property name="major"/>
	</class>
</hibernate-mapping>
三、组合关系映射 (一个类和中有另一个类的引用，并将两个类组合成为一个表)

<hibernate-mapping 
	package="com.bjsxt.po">
	<class name="Person" table="t_person" >
		<id name="id">
			<generator class="native"></generator>
		</id>
		<component name="address" class="Address"> <!-- 这里的address是另外一个类 
                          Pserson类持有Address类的引用--!>
			<property name="city"></property>
			<property name="street"></property>
			<property name="zipcode"></property>
		</component>
		<property name="name"></property>
	</class>
</hibernate-mapping>
四、大对象映射
     所谓的大对象其实不过是数据库中的一种类型，可以将视频或者 图片存入到数据库中。
     使用是若用mysql要注意添加一个转码.同时调整mysql中的Blob 为longBlob
     jdbc:mysql://localhost:3306/hib?useUnicode=true&characterEncoding=utf-8
五、关联映射
   1.一对一映射
     1.1唯一外键关连
public class Company {
	
	private int id;
	private String name;
	private Address2 address2;   持有外键的对象
        //get set 方法
}
public class Address2 {
	private int id;
	private String city;
	private String country;
	private Company company;
}
<hibernate-mapping package="com.bjsxt.po">
	<class name="Company" table="t_company">
		<id name="id">
			<generator class="native"></generator>
		</id>
		<property name="name"/>
		<many-to-one name="address2" class="Address2"
                    unique="true" 
                 cascade="all" >
                 <column name="addressId"/>
                </many-to-one>
	</class>	
</hibernate-mapping>
<hibernate-mapping package="com.bjsxt.po">
	<class name="Address2" table="t_address2">
		<id name="id">
			<generator class="native"></generator>
		</id>
		<property name="city"/>
		<property name="country"/>
		<one-to-one name="company" class="Company"  
       property-ref="address2"     cascade="save-update">  //此property-ref指的是外键，也就是从address2中找外键 
               </one-to-one>
	</class>	
</hibernate-mapping>
     1.2主键关联和唯一关联几乎一样 ,唯一的关别在于 将many-to-one 改成one-to-one 删除property-ref 和unique