Hibernate中createCriteria（QBC）查詢的用法

如今假設有一個Student類,內有id,name,age屬性 
String hql = "from Student s"; 
按照之前的作法,咱們一般是 
Query query = session.createQuery(hql); 
或者要按照條件檢索的話. 
String hql = "from Student s where s.name like '王%'" 
Query query = session.createQuery(hql); 
不用HQL而使用QBC的話,那麼代碼爲: 
Criteria criteria =session.createCriteria(Student.class); 
Criterion criterion = Expression.like("name","王%"); 
這樣還看不出來.那咱們把檢索條件加上年齡爲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(); 


看上去煩瑣不少.可是作過項目的人都知道,當一個模塊業務邏輯發生改變的時候,每每要重寫sql,最煩也是最討厭的就是拿着別人的hql或者sql,兩眼瞪的溜園找到底要修改什麼地方呢? 
若是使用QBC大大的增長了代碼的可讀性,以及可維護性. 
須要注意的是null值 
好比咱們要查找姓名爲null的Student對象時應該這麼寫 
Criteria criteria =session.createCriteria(Student.class); 
Criterion criterion = Expression.isNull("name"); 
criteria.add(criterion).list(); 
以及使用between...and的時候 
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 
//這裏也能夠把上述兩個條件添加到第三個條件裏 
Criterion criterion3 =Expression.and(criterion1,criterion2); 
criteria.add(criterion3).list(); 
至關於from Student s where s.age between 20 and 25 
等同於from Student s where s.age >= 20 and s.age <=25 


下面是就HQL和QBC經常使用的查詢條件作的比較 
表達式含義                                     HQL                                     QBC 
大於等於                                         >=                                        Expression.ge() 
大於                                                 >                                         Expression.gt() 
小於等於                                         <=                                        Expression.le() 
小於                                                 <                                         Expression.lt() 
等於                                                 =                                         Expression.eq() 
不等於                                             <>或者!=                            Expression.ne()    

爲空                                                 is null                             Expression.isNull() 
不爲空                                             is notnull                        Expression.isNotNull() 
在指定範圍內                                 betweenand                        Expression.between() 
不在指定範圍                                 not betweenand                Expression.not(Expression.between()) 
屬於某個集合                                 in                                        Expression.in() 
不屬於某個集合                             notin                                 Expression.not(Expression.in()) 
與                                                    and                                     Expression.and() 
或                                                    or                                        Expression.or() 
非                                                    not                                     Expression.not() 
模糊查詢                                        like                                    Expression.like