二。Hibernate 查询 HQL、SQL方式

hibernate的查询
1.HQL方式：所有查询都是根据java对象名来完成，对象名替换表名
2.SQL方式：保留原来的sql查询风格
3.可以通过设置第一条和最大条数来实现各种数据库的分页查询
4.通过BaseDAO来实现dao的代码优化

实例1：hql、sql查询

　　Test.java

package com.dao;

import java.util.Date;
import java.util.List;

import org.hibernate.*;
import org.hibernate.cfg.*;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;

import com.pojo.Student;

public class Test {

    public static void main(String[] args) {
        // 配置对象，用来获取核心配置文件的
        // 如果核心配置文件名是：hibernate.cfg.xml,并且该文件在src根目录下，configure（）可以不带参数
        Configuration configuration = new Configuration().configure();
        ServiceRegistry sr = new ServiceRegistryBuilder().applySettings(configuration.getProperties())
                .buildServiceRegistry();
        SessionFactory sf = configuration.buildSessionFactory(sr);
        Session session = sf.openSession();
        
        //1.hql:是hibernate的专用查询语句，是针对对象的查询方法，其中没有表名，全都是对象名
        String hql = "from Student";
//        String hql = "select count(*) from Student a";
        Query query = session.createQuery(hql);
        query.setFirstResult(5);
        query.setMaxResults(5);
        List<Student> list = query.list();
//        System.out.println(list.get(0));
//        for (Student stu : list) {
//            System.out.println(stu.getClassId()+"	"+stu.getStudentName());
//        }
        
        //2.sql：用传统的sql语句来完成查询
        String sql = "select * from Student_info";
        SQLQuery squery = session.createSQLQuery(sql);
        squery.addEntity(Student.class);//指明结果封装对象
        squery.setFirstResult(5);
        squery.setMaxResults(5);
        List<Student> list2 = squery.list();
        for (Student stu : list2) {
            System.out.println(stu.getClassId()+"	"+stu.getStudentName());
        }
        
        session.flush();
        session.close();
    }

}

实例2：写一个分页查询的dao方法

　　Test2.java

package com.dao;

import java.util.List;

import com.pojo.Student;

public class Test2 {
    public static void main(String[] args) {
        IStudentDAO stuDAO = new StudentDAO();

        List<Student> list = stuDAO.queryStudentByPage(2, 5, "from Student");
        for (Student stu : list) {
            System.out.println(stu.getStudentName());
        }
    }
}

　　IStudentDAO.java

package com.dao;

import java.util.List;

import com.pojo.Student;

public interface IStudentDAO extends IBaseDAO<Student>{
    public List<Student> queryStudentByPage(int index,int pagecount,String hql);
}

　　Student.java

package com.dao;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.SQLQuery;
import org.hibernate.Session;

import com.pojo.Student;

public class StudentDAO extends BaseDAO<Student> implements IStudentDAO{

    @Override
    public List<Student> queryStudentByPage(int index, int pagecount,String hql) {
        Session session = getSession();

        Query hq = session.createQuery(hql);
        hq.setFirstResult((index-1)*pagecount);
        hq.setMaxResults(pagecount);

        List<Student> list = hq.list();

        session.flush();
　　　　 session.close();

        return list;
    }
    
}

附：IBaseDao.java

package com.dao;

import java.util.List;

import org.hibernate.Session;

public interface IBaseDAO<T> {

    Session getSession();

    void saveObject(T t);

    void delObject(T t);

    void updateObject(T t);

    List<T> queryObjectByHql(String hql);

    List<T> queryObjectBySql(String sql, Class t);

}

　　BaseDao.java

package com.dao;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.SQLQuery;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;

import com.pojo.Student;


public class BaseDAO<T> implements IBaseDAO<T> {
    public Session getSession() {
        // 配置对象，用来获取核心配置文件的
        // 如果核心配置文件名是：hibernate.cfg.xml,并且该文件在src根目录下，configure（）可以不带参数
        Configuration configuration = new Configuration().configure();
        ServiceRegistry sr = new ServiceRegistryBuilder().applySettings(configuration.getProperties())
                .buildServiceRegistry();
        SessionFactory sf = configuration.buildSessionFactory(sr);
        Session session = sf.openSession();
        return session;
    }
    
    public void saveObject(T t) {
        Session session = getSession();
        session.save(t);
        session.beginTransaction().commit();
        session.close();
    }

    public void delObject(T t) {
        Session session = getSession();
        session.delete(t);
        session.beginTransaction().commit();
        session.close();
    }

    public void updateObject(T t) {
        Session session = getSession();
        session.update(t);
        session.beginTransaction().commit();
        session.close();
    }

    public List<T> queryObjectByHql(String hql) {
        Session session = getSession();
        Query query = session.createQuery(hql);
        List<T> list = query.list();
        session.flush();
        session.close();
        return list;
    }

    public List<T> queryObjectBySql(String sql,Class t) {
        Session session = getSession();
        SQLQuery sq = session.createSQLQuery(sql);
        sq.addEntity(t);
        List<T> list = sq.list();
        session.flush();
        session.close();
        return list;
    }
}