Hibernate中createCriteria即QBC查詢的詳細用法

現在假設有一個Student類,內有id,name,age屬性
String hql = "from Student s";
按照以前的做法,我們通常是
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,那么代碼為:
Criteria criteria =session.createCriteria(Student. class);
Criterion criterion = Expression.like( "name", "王%");
這樣還看不出來.那我們把檢索條件加上年齡為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();


看上去煩瑣很多.但是做過項目的人都知道,當一個模塊業務邏輯發生改變的時候,往往要重寫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么地方呢?
如果使用QBC大大的增加了代碼的可讀性,以及可維護性.
需要注意的是 null值
比如我們要查找姓名為 null的Student對象時應該這么寫
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
//這里也可以把上述兩個條件添加到第三個條件里
Criterion criterion3 =Expression.and(criterion1,criterion2);
criteria.add(criterion3).list();
相當於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常用的查詢條件做的比較
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()    

為空                                                 is null                             Expression.isNull()
不為空                                             is notnull                        Expression.isNotNull()
在指定范圍內                                 betweenand                        Expression.between()
不在指定范圍                                 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