HQL查询的使用

HQL查询的实现：

HQL为面向对象的查询语言，与SQL不同，HQL中的对象名是区分大小写的（除了JAVA类和属性其他部分不区分大小写）；HQL中查的是对象而不是和表，并且支持多态；HQL主要通过Query来操作。下面我用一个实例简单理解HQL的查询语句：

 

一、javaBean代码的编写：

 

public class User {

 

    private Integer id;

    private String name;

    private Date birthday;

    public Integer getId() {

       return id;

    }

    public void setId(Integer id) {

       this.id = id;

    }

    public String getName() {

       return name;

    }

    public void setName(String name) {

       this.name = name;

    }

    public Date getBirthday() {

       return birthday;

    }

    public void setBirthday(Date birthday) {

       this.birthday = birthday;

    }

   

}

 

二、导入相应的hibernate.jar和其依赖的包

三、编写User.hbm.xml映射文件

 

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

 

<hibernate-mapping package="com.hbsi.domain">

 

    <class name="User" table="user">

       <id name="id"><!-- unsaved-value判定是瞬时的还是脱管的 -->

           <generator class="native"/>

       </id>

       <property name="name"/>

       <property name="birthday"/>

    </class>

</hibernate-mapping>

四、编写hibernate.cfg.xml配置文件

<!DOCTYPE hibernate-configuration PUBLIC

    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

 

<hibernate-configuration>

    <session-factory name="foo">

       <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

       <property name="connection.url">jdbc:mysql:///demo</property>

       <property name="hibernate.connection.username">root</property>

       <property name="connection.password">123</property>

       <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

       <property name="hibernate.hbm2ddl.auto">update</property>

       <property name="hibernate.show_sql">true</property>

      

       <mapping resource="com/hbsi/domain/User.hbm.xml"/>

    </session-factory>

</hibernate-configuration>

 

五、编写方法实现query查询

 

public static void query(String name) {

       Session session = null;

       try {

           session = HibernateUtil.getSession();

           /* StringqueryString =

            "from Useruser where user.name=?";//hibernate的查询语言

*/         String queryString = "from User user where user.name=:n";// 命名参数

           Query query = session.createQuery(queryString);

           //query.setString(0, name);

           query.setString("n", name);

           //可实现分页显示

           query.setFirstResult(0);// 从哪行开始

           query.setMaxResults(2);// 一页显示几行

 

           /*

            * List<User>list=query.list();//多行的结果集 for(User user:list){

            *System.out.println(user.getId()+":"+user.getBirthday()); }

            */

           User user = (User) query.uniqueResult();// 得到一行的结果集.(明确知道有一行，如果有多行就会有异常)

           System.out.println(user.getId());

       } finally {

           if (session != null) {

              session.close();

           }

       }

    }