BlogJava-强大的心-随笔分类-hibernate note

Hibernate 批量查询和更新优化

simplye — Mon, 16 Mar 2009 10:03:00 GMT

在hibernate.cfg.xml配置文件中配置
50
//每次查询50条
50
//每次更新50条

simplye 2009-03-16 18:03 发表评论

HQL 统计查询语句

simplye — Thu, 05 Mar 2009 14:43:00 GMT

1 List students =session.createQuery("select c.name, count(s) from Student s join s.classes c " +
2                     "group by c.name order by c.name").list();
3             for (Iterator iter=students.iterator(); iter.hasNext();) {
4                 Object[] obj = (Object[])iter.next();
5                 System.out.println(obj[0] + ", " + obj[1]);
6             }

simplye 2009-03-05 22:43 发表评论

HQL 连接查询语句

simplye — Thu, 05 Mar 2009 14:37:00 GMT

1.
List students = session.createQuery("select c.name, s.name from Student s inner join s.classes c").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + "," + obj[1]);
            }

2.
//左连接
List students = session.createQuery("select c.name, s.name from Classes c left join c.students s").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + "," + obj[1]);
            }

simplye 2009-03-05 22:37 发表评论

HQL 语句---简单属性查询

simplye — Wed, 04 Mar 2009 09:17:00 GMT

1.
/**
单一属性查询
*/
List s = session.createQuery("select name from Student").list();
//返回的类型与实体类中相应的属性类别一直.

2.
/**
多个属性查询
*/
List s = session.createQuery("select id, name from Student").list();
//查询多个属性,返回值为对象的数组
//数组元素类型和对应的实体类型一直
//数组长度与查询的条件相同

3./**
返回student实体类,
还要在实体类中提供空的构造函数,和带参数的构造函数
*/
List s = session.createQuery("select new Student(id, name) from Student").list();
//返回的便是实体类

4.
可以实用别名,用as

5.
/*
list()与iterate()方法的区别.
*/
iterate()迭代中会发生N+1的现象,它与session的绑定.当session在缓存中存在时用iterate()会提高一定的效率.没有在发生N+1现象
list()只会向数据库查询的SQL,除非配置查询缓存.

simplye 2009-03-04 17:17 发表评论

Hibernate 悲观锁与乐观锁

simplye — Wed, 04 Mar 2009 06:39:00 GMT

/*
悲观锁
*/
Inventory inv = (Inventory)session.load(Inventory.class, 1, LockMode.UPGRADE);
// 在数据库设置为不可重复读下设置,LockMode为枚举类型.

/*
乐观锁
*/
Inventory inv = (Inventory)session.load(Inventory.class, 1);
// 在映射文件中添加字段,在读取时读取version字段进行判断,如果version数值小于等于当前数值则报错.

simplye 2009-03-04 14:39 发表评论

Hibernate collection映射

simplye — Tue, 03 Mar 2009 09:59:00 GMT

          <id name="id">
              <generator class="native"/>
         id>
         <property name="name"/>

         <set name="setValue" table="t_set_value">   // set的映射
                 <key column="set_id"/>                   // 外键关联
      //

对象集合

                 <element type="string" column="set_value">        // 字符串集合放入表中
         set>

         <list name="listValue" table="t_list_value">   //list的映射
                 <key column="list_id"/>
                 <list-index column="list_index"/>                        // 将存入表数据排序放入一个字段中
                 <element type="string" column="list_value"/>
         list>

         <array name="arrayValue" table="t_array_value">
                 <key column="array_id"/>
                 <array-index column="array-index"/>
                 <element type="string" column="array_value"/>
         array>

         <map name="mapValue" table="t_map_value">
                 <key column="map_id" />
                 <map-key type="string" column="map_key"/>     //存放map中的key值
                 <element type="string" column="map_value"/> //存放map中的value值
         map>
     class>
hibernate-mapping>

simplye 2009-03-03 17:59 发表评论

Hibernate many2one映射

simplye — Mon, 02 Mar 2009 06:43:00 GMT

1 xml version="1.0"?>
2 DOCTYPE hibernate-mapping PUBLIC
3     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
4     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
5 <hibernate-mapping >
6     <class name="com.simplye.hibernate.User" table="t_user">
7         <id name="id">
8             <generator class="native"/>
9         id>
10         <property name="name"/>
11
12         <many-to-one name="group" column="t_group"/>
13
14     class>
15 hibernate-mapping>

多段实用外键

1 xml version="1.0"?>
2 DOCTYPE hibernate-mapping PUBLIC
3     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
4     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
5 <hibernate-mapping >
6     <class name="com.simplye.hibernate.Group" table="t_group">
7         <id name="id">
8             <generator class="native"/>
9         id>
10         <property name="name"/>
11     class>
12 hibernate-mapping>

simplye 2009-03-02 14:43 发表评论

Hibernate component映射

simplye — Sun, 01 Mar 2009 17:53:00 GMT

  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.simplye.hibernate">
      <class name="User" table="t_user">
          <id name="id">
            <generator class="native"/>
          id>
         <property name="name"/>
           <component name="contact"> //附属类
               <property name="email">
           component>
     class>
hibernate-mapping>

simplye 2009-03-02 01:53 发表评论

Hibernate 继承类映射----每个具体类使用一张表

simplye — Sun, 01 Mar 2009 17:26:00 GMT

class>
hibernate-mapping>

simplye 2009-03-02 01:26 发表评论

Hibernate 继承类映射----每个子类使用一张表

simplye — Sun, 01 Mar 2009 14:46:00 GMT

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.simplye.hibernate">
    <class name="Animal" table="t_animal">
        <id name="id">
            <generator class="native"/>
        id>
        <property name="name"/>
        <property name="sex"/>
        <joined-subclass name="Pig" table="t_pig">
            <key column="pig"/>
            <property name="weight"/>
        joined-subclass>
        <joined-subclass name="Bird" table="t_brid">
            <key column="brid"/>
            <property name="height"/>
        joined-subclass>
    class>
hibernate-mapping>

simplye 2009-03-01 22:46 发表评论

Hibernate 继承类映射----每棵类树使用一张表

simplye — Sun, 01 Mar 2009 14:38:00 GMT

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.simplye.hibernate">
    <class name="Animal" table="t_animal">
        <id name="id">
            <generator class="native"/>
        id>
        <discriminator column="type" type="string"/>
        <property name="name"/>
        <property name="sex"/>
        <subclass name="Pig" discriminator-value="P">
        <property name="weight"/>
    subclass>
    <subclass name="Bird" discriminator-value="B">
        <property name="height" />
    subclass>
    class>
hibernate-mapping>

simplye 2009-03-01 22:38 发表评论