Hibernate中createCriteria即QBC查询的详细用法

转自：https://blog.csdn.net/qq_36484521/article/details/54174721

现在假设有一个Student类,内有id,name,age属性
String hql = "from Student s";
按照以前的做法,我们通常是
Query query = session.createQuery(hql);
或者要按照条件检索的话.
String hql = "from Student s where s.name like '王%'"
Query query = session.createQuery(hql);
不用HQL而使用QBC的话,那么代码为:
Criteria criteria =session.createCriteria(Student.class);
Criterion criterion = Expression.like("name","王%");
这样还看不出来.那我们把检索条件加上年龄为22.
HQL:
String hql = "from Student s where s.name like '王%' and s.age= 22 ";
Query query = session.createQuery(hql);
List list = query.list();
QBC:
Criteria criteria =session.createCriteria(Student.class);
Criterion criterion1 = Expression.like("name","王%");
Criterion criterion2 = Expression.eq("age",newInteger(22));
criteria.add(criterion1).add(criterion2);
List list = criteria.list();


看上去烦琐很多.但是做过项目的人都知道,当一个模块业务逻辑发生改变的时候,往往要重写sql,最烦也是最讨厌的就是拿着别人的hql或者sql,两眼瞪的溜园找到底要修改什么地方呢?
如果使用QBC大大的增加了代码的可读性,以及可维护性.
需要注意的是null值
比如我们要查找姓名为null的Student对象时应该这么写
Criteria criteria =session.createCriteria(Student.class);
Criterion criterion = Expression.isNull("name");
criteria.add(criterion).list();
以及使用between...and的时候
Criteria criteria =session.createCriteria(Student.class);
Criterion criterion1 = Expression.ge("age",new Integer(20));//下限
Criterion criterion2 = Expression.le("age",new Integer(25));//上限
//这里也可以把上述两个条件添加到第三个条件里
Criterion criterion3 =Expression.and(criterion1,criterion2);
criteria.add(criterion3).list();
相当于from Student s where s.age between 20 and 25
等同于from Student s where s.age >= 20 and s.age <=25


下面是就HQL和QBC常用的查询条件做的比较
表达式含义                                     HQL                                     QBC
大于等于                                         >=                                        Expression.ge()
大于                                                 >                                         Expression.gt()
小于等于                                         <=                                        Expression.le()
小于                                                 <                                         Expression.lt()
等于                                                 =                                         Expression.eq()
不等于                                             <>或者!=                            Expression.ne()    

为空                                                 is null                             Expression.isNull()
不为空                                             is notnull                        Expression.isNotNull()
在指定范围内                                 betweenand                        Expression.between()
不在指定范围                                 not betweenand                Expression.not(Expression.between())
属于某个集合                                 in                                        Expression.in()
不属于某个集合                             notin                                 Expression.not(Expression.in())
与                                                    and                                     Expression.and()
或                                                    or                                        Expression.or()
非                                                    not                                     Expression.not()
模糊查询                                        like                                    Expression.like