Hibernate中的QBC查询方式详解

比眉伴天荒 2022-12-03 08:38 114阅读 0赞

#### 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。

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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();
        }
    }

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（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();
        }
    }

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