Hibernate中的QBC查询方式详解-蒲公英云

Hibernate中的QBC查询方式详解

QBC：Query By Criteria，条件查询。

是一种更加面向对象化的查询的方式。

1、QBC简单查询

测试代码：

package com.pipi.hibernate05;
import com.pipi.hibernate04.Dept;
import myutils.HibernateUtil;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.Transaction;
import java.util.List;
// QBC简单查询：查询表中所有记录
public class Test01_QBC { 
    public static void main(String[] args) { 
        Session session = HibernateUtil.getCurrentSession();
        Transaction transaction = session.beginTransaction();
        // 简单查询
        Criteria criteria = session.createCriteria(Dept.class);
        List<Dept> list = criteria.list();
        for (Dept d : list) { 
            System.out.println(d);
        }
        transaction.commit();
    }
}

（2）QBC排序查询

测试代码：

package com.pipi.hibernate05;
import com.pipi.hibernate04.Dept;
import myutils.HibernateUtil;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.criterion.Order;
import java.util.List;
// QBC排序查询
public class Test02_QBC { 
    public static void main(String[] args) { 
        Session session = HibernateUtil.getCurrentSession();
        Transaction transaction = session.beginTransaction();
        // 排序查询
        Criteria criteria = session.createCriteria(Dept.class);
        //criteria.addOrder(Order.asc("deptno")); // 升序
        criteria.addOrder(Order.desc("deptno"));  // 降序
        List<Dept> list = criteria.list();
        for (Dept d : list) { 
            System.out.println(d);
        }
        transaction.commit();
    }
}

（3）QBC分页查询

测试代码：

package com.pipi.hibernate05;
import com.pipi.hibernate04.Emp;
import myutils.HibernateUtil;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.Transaction;
import java.util.List;
// QBC的分页查询
public class Test03_QBC { 
    public static void main(String[] args) { 
        Session session = HibernateUtil.getCurrentSession();
        Transaction transaction = session.beginTransaction();
        // 分页查询
        Criteria criteria = session.createCriteria(Emp.class);
        criteria.setFirstResult(0);
        criteria.setMaxResults(5);
        List<Emp> list = criteria.list();
        for (Emp e : list) { 
            System.out.println(e);
        }
        transaction.commit();
    }
}

（4）QBC条件查询

测试代码：

package com.pipi.hibernate05;
import com.pipi.hibernate04.Emp;
import myutils.HibernateUtil;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.criterion.Restrictions;
import java.util.List;
/* criteria.add(Restrictions.xxx()) = eq > gt >= ge < lt <= le <> ne like in and or between */
// QBC的条件查询
public class Test04_QBC { 
    public static void main(String[] args) { 
        Session session = HibernateUtil.getCurrentSession();
        Transaction transaction = session.beginTransaction();
        // 条件查询
        Criteria criteria = session.createCriteria(Emp.class);
        criteria.add(Restrictions.like("ename", "Smi%"));
        //criteria.add(Restrictions.or(Restrictions.eq("job", "Clerk")));
        criteria.add(Restrictions.eq("job", "Clerk"));
        List<Emp> list = criteria.list();
        for (Emp e : list) { 
            System.out.println(e);
        }
        transaction.commit();
    }
}

（5）QBC统计分组查询

测试代码：

package com.pipi.hibernate05;
import com.pipi.hibernate04.Emp;
import myutils.HibernateUtil;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.criterion.Projections;
// QBC的统计分组查询
public class Test05_QBC { 
    public static void main(String[] args) { 
        Session session = HibernateUtil.getCurrentSession();
        Transaction transaction = session.beginTransaction();
        Criteria criteria = session.createCriteria(Emp.class);
        /* add : 普通的条件，where后面的条件 addOrder : 排序 setProjection : 聚合函数 和 group by having */
        criteria.setProjection(Projections.rowCount());
        Long cnt = (Long) criteria.uniqueResult();
        System.out.println(cnt);  // 14
        transaction.commit();
    }
}

（6）QBC离线条件查询：DetachedCriteria

什么是QBC离线查询？

往往在Web层时，就可以设置QBC语句，及查询条件。
但在Web层是没有Session对象的，Session是Dao层的。
此时可以使用离线查询DetachedCriteria对象。

测试代码：

package com.pipi.hibernate05;
import com.pipi.hibernate04.Emp;
import myutils.HibernateUtil;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.criterion.DetachedCriteria;
import org.hibernate.criterion.Restrictions;
import java.util.List;
// QBC离线条件查询：DetachedCriteria
public class Test06_QBC { 
    public static void main(String[] args) { 
        // 在创建Session对象之前，就可以创建DetachedCriteria，并设置条件
        DetachedCriteria detachedCriteria = DetachedCriteria.forClass(Emp.class);
        detachedCriteria.add(Restrictions.eq("ename", "Smith"));
        // 创建Session对象
        Session session = HibernateUtil.getCurrentSession();
        Transaction transaction = session.beginTransaction();
        // 将DetachedCriteria对象与Session绑定，返回Criteria对象
        Criteria criteria = detachedCriteria.getExecutableCriteria(session);
        List<Emp> list = criteria.list();
        for (Emp e : list) { 
            System.out.println(e);
        }
        transaction.commit();
    }
}