HQL查询及Hibernate对c3p0连接池的支持

        //HQL查询
        // auto-import要设置true，如果是false，写HQL时要指定类的全名
        //查询全部列
        Query query = session.createQuery("from Dept");
        System.out.println(query.list());

        //查询指定列
        Query query = session.createQuery("select d.depId,d.depName from Dept d");
        System.out.println(query.list());

        //查询指定列，并封装为对象，必须提供带参数的构造器
        Query query = session.createQuery("select new Dept(d.depId,d.depName) from Dept d");
        System.out.println(query.list());

        //条件查询 一个条件、多个条件、and or between 模糊查询
        Query query = session.createQuery("from Dept d where depName=?");
        query.setString(0,"人事部");
        query.setParameter(0,"人事部");
        //条件查询，命名参数
        Query query = session.createQuery("from Dept d where depId =:myid and depName=:name");
        query.setParameter("myid",1);
        query.setParameter("name","人事部");
        //条件查询，between and查询
        Query query = session.createQuery("from Dept d where depId between ? and ?");
        query.setParameter(0,1);
        query.setParameter(1,5);
        //模糊查询
        Query query = session.createQuery("from Dept d where depName like ?");
        query.setParameter(0,"%部%");
        System.out.println(query.list());

        //集合函数统计，不支持count(1)，uniqueResult()返回结果的第一行第一列中的值
        Query query = session.createQuery("select count(*) from Dept");
        System.out.println(query.uniqueResult());

        //分组查询，查询employ表，统计每个部门的人数
        Query query = session.createQuery("select e.dept, count(*) from Employee e group by e.dept");
        //统计部门人数大于1的部门
        Query query = session.createQuery("select e.dept, count(*) from Employee e group by e.dept having count(*) >1");
        System.out.println(query.list());

        //连接查询，内连接、左外连接、右外连接
        //内连接，映射已经配置好了关系，关联的时候直接写对象的属性即可
        //返回员工和部门组成的对象数组，写在前面的元素在结果集中也在前面
//        SELECT e.empName, e.salary, d.deptName FROM t_employee e INNER JOIN t_dept d ON d.depId = e.dept_id
        Query query = session.createQuery("select e.empName,e.salary,e.dept.depName from Employee e inner join e.dept");
        List<Object[]> list = query.list();
        for(int i=0;i<list.size();i++){
            Object[] obj = list.get(i);
            Employee employee = (Employee) obj[0];
            Dept dept = (Dept) obj[1];
            System.out.println(employee);
            System.out.println(dept);
        }
        System.out.println(query.list());
        //左外连接
//        SELECT e.empName, e.salary, d.deptName FROM t_employee e LEFT JOIN t_dept d ON d.depId = e.dept_id
        Query query = session.createQuery(" from Employee e left join e.dept");
        List<Object[]> list = query.list();
        for(int i=0;i<list.size();i++){
            Object[] obj = list.get(i);
            Employee employee = (Employee) obj[0];
            Dept dept = (Dept) obj[1];
            System.out.println(employee);
            System.out.println(dept);
        }//迫切内连接，将右表的对象填充到左表当中
        Query query = session.createQuery("from Dept d inner join fetch d.emps");

将HQL查询语句放到映射文件中：

    <query name="getDept">
        from Dept d where depName=?
    </query>
    <query name="getDept2">
        <![CDATA[
            from Dept d where depId < ?
        ]]>
    </query>

使用查询语句

        Query query = session.getNamedQuery("getDept");
        query.setParameter(0,"人事部");

        Query query = session.getNamedQuery("getDept2");
        query.setParameter(0, 4);
        System.out.println(query.list());

 使用c3p0连接池

<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <!-- 通常，一个session-factory节点代表一个数据库 -->
    <session-factory>
    
        <!-- 1. 数据库连接配置 -->
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql:///test</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">juaner767</property>
        <!-- 【连接池配置】 -->
        <!-- 
            数据库方法配置， hibernate在运行的时候，会根据不同的方言生成符合当前数据库语法的sql
         -->
        <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
        
        
        <!-- 2. 其他相关配置 -->
        <!-- 2.1 显示hibernate在运行时候执行的sql语句 -->
        <property name="hibernate.show_sql">true</property>
        <!-- 2.2 格式化sql
        <property name="hibernate.format_sql">true</property>  -->
        <!-- 2.3 自动建表  -->
        <property name="hibernate.hbm2ddl.auto">update</property>

        <!-- 配置连接驱动管理类 -->
        <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
        <!-- 配置连接池参数信息 -->
        <property name="hibernate.c3p0.min_size">2</property>
        <property name="hibernate.c3p0.max_size">4</property>
        <property name="hibernate.c3p0.timeout">5000</property>
        <property name="hibernate.c3p0.max_statements">10</property>
        <property name="hibernate.c3p0.idle_test_period">30000</property>
        <property name="hibernate.c3p0.acquire_increment">2</property>
        
        <!-- 3. 加载所有映射 -->
        <mapping resource="com/juaner/hibernate/address/User.hbm.xml"/>
        <!--<mapping resource="com/juaner/hibernate/department/Dept.hbm.xml"/>-->
        <!--<mapping resource="com/juaner/hibernate/department/Employee.hbm.xml"/>-->
        <!--<mapping resource="com/juaner/hibernate/project/Developer.hbm.xml"/>-->
        <!--<mapping resource="com/juaner/hibernate/project/Project.hbm.xml"/>-->
        <!--<mapping resource="com/juaner/hibernate/extendMap/Animal.hbm.xml"/>-->
    </session-factory>
</hibernate-configuration>