1.HQL查詢

• HQL(Hibernate Query Language)提供了豐富靈活的查詢方式，使用HQL進行查詢也是Hibernate官方推薦使用的查詢方式。

• HQL在語法結構上和SQL語句十分的相同，所以可以很快的上手進行使用。使用HQL需要用到Hibernate中的Query對象，該對象專門執行HQL方式的操作。

查詢所有示例

session.beginTransaction();
String hql = "from User"; // from 后跟的是要查詢的對象，而不是表
Query query = session.createQuery(hql);
List<User> userList = query.list();
for(User user:userList){
System.out.println(user.getUserName());
}
session.getTransaction().commit();

帶where的查詢示例

session.beginTransaction();
String hql = "from User where userName = 'James'";
Query query = session.createQuery(hql);
List<User> userList = query.list();
for(User user:userList){
System.out.println(user.getUserName());
}
session.getTransaction().commit();
/*
在HQL中where語句中使用的是持久化對象的屬性名，如上面示例中的userName。當然在HQL中也可以使用別名
*/
String hql = "from User as u where u.userName = 'James'";
/*
過濾條件
在where語句中還可以使用各種過濾條件，如：=、<>、<、>、>=、<=、between、not between、
in、not in、is、like、and、or等
*/

獲取一個不完整的對象

session.beginTransaction();
String hql = "select userName from User";
Query query = session.createQuery(hql);
List<Object> nameList = query.list();
for(Object obj:nameList){
　　 String name=(String)obj;
　　 System.out.println(name);
}
session.getTransaction().commit();
// 多個屬性的話，需要用object[]接收
session.beginTransaction();
String hql = "select userName,userPwd from User";
Query query = session.createQuery(hql);
List nameList = query.list();
for(Object obj:nameList){
Object[] array = (Object[]) obj; // 轉成object[]
System.out.println("name:" + array[0]);
System.out.println("pwd:" + array[1]);
}
session.getTransaction().commit();

統計和分組查詢

session.beginTransaction();
String hql = "select count(*),max(id) from User";
Query query = session.createQuery(hql);
List nameList = query.list();
for(Object obj:nameList){
Object[] array = (Object[]) obj;
System.out.println("count:" + array[0]);
System.out.println("max:" + array[1]);
}
session.getTransaction().commit();
/*
該條sql語句返回的是單條數據，所以還可以這樣寫
單列數據用Object，多列數據用Object[]
*/
Object[] object = (Object[]) query.uniqueResult();
System.out.println("count:" + object[0]);
System.out.println("max:" + object[1]);

更多寫法

select distinct name from Student;
select max(age) from Student;
select count(age),age from Student group by age;
from Student order by age;

HQL占位符

session.beginTransaction();
String hql = "from User where userName = ?";
Query query = session.createQuery(hql);
// 索引從0開始
query.setString(0, "James");
List<User> userList = query.list();
for(User user:userList){
System.out.println(user.getUserName());
}
session.getTransaction().commit();

HQL引用占位符

session.beginTransaction();
String hql = "from User where userName = :name";
Query query = session.createQuery(hql);
query.setParameter("name", "James");
List<User> userList = query.list();
for(User user:userList){
System.out.println(user.getUserName());
}
session.getTransaction().commit();

HQL分頁

session.beginTransaction();
String hql = "from User";
Query query = session.createQuery(hql);
query.setFirstResult(0);
query.setMaxResults(2);
List<User> userList = query.list();
for(User user:userList){
System.out.println(user.getUserName());
}
session.getTransaction().commit();

2.QBC(Query By Criteria)查詢

• Criteria對象提供了一種面向對象的方式查詢數據庫。Criteria對象需要使用Session對象來獲得。

• 一個Criteria對象表示對一個持久化類的查詢。

查詢所有

session.beginTransaction();
Criteria c = session.createCriteria(User.class);
List<User> userList = c.list();
for(User user:userList){
System.out.println(user.getUserName());
}
session.getTransaction().commit();

where

session.beginTransaction();
Criteria c = session.createCriteria(User.class);
c.add(Restrictions.eq("userName", "James"));
List<User> userList = c.list();
for(User user:userList){
System.out.println(user.getUserName());
}
session.getTransaction().commit();

Restrictions對象

方法名稱 對應SQL中的表達式
----------------------------------------------------------
Restrictions.eq field = value
Restrictions.gt field > value
Restrictions.lt field < value
Restrictions.ge field >= value
Restrictions.le field <= value
Restrictions.between field between value1 and value2
Restrictions.in field in(…)
Restrictions.and and
Restrictions.or or
Restrictions.like field like value

示例

Criteria c = session.createCriteria(User.class);
c.add(Restrictions.like("userName", "J"));
c.add(Restrictions.eq("id", 120));
c.add(Restrictions.or(Restrictions.eq("userName", "James"),
Restrictions.eq("userName", "Alex")));

獲取唯一記錄

session.beginTransaction();
Criteria c = session.createCriteria(User.class);
c.add(Restrictions.eq("id", 120));
User user = (User) c.uniqueResult();
System.out.println(user.getUserName());
session.getTransaction().commit();

分頁

Criteria c = session.createCriteria(User.class);
c.setFirstResult(0);
c.setMaxResults(5);

分組與統計

session.beginTransaction();
Criteria c = session.createCriteria(User.class);
c.setProjection(Projections.sum("id"));
Object obj = c.uniqueResult();
System.out.println(obj);
session.getTransaction().commit();

Projections對象

方法名稱 描述
-------------------------------------------------------
Projections.sum 等于SQL中聚合函數sum
Projections.avg 等于SQL中聚合函數avg
Projections.count 等于SQL中聚合函數count
Projections .distinct 去除重復記錄
Projections.max 等于SQL中聚合函數max
Projections.min 等于SQL中聚合函數min
Projections .groupProperty 對指定的屬性進行分組查詢

多個統計與分組

session.beginTransaction();
Criteria c = session.createCriteria(User.class);
ProjectionList projectionList = Projections.projectionList();
projectionList.add(Projections.sum("id"));
projectionList.add(Projections.min("id"));
c.setProjection(projectionList);
// 和HQL一樣，單列用Object，多列用Object[]
Object[] obj = (Object[]) c.uniqueResult();
System.out.println("sum:" + obj[0]);
System.out.println("min:" + obj[1]);

排序

Criteria c = session.createCriteria(User.class);
c.addOrder(Order.desc("id"));

3.原生SQL查詢：

示例

session.beginTransaction();
String sql = "select id,username,userpwd from t_user";
List list = session.createSQLQuery(sql).list();
for(Object item : list){
Object[] rows = (Object[]) item;
System.out.println("id:" + rows[0] + "username:"
+ rows[1] + "userpwd:" + rows[2]);
}
session.getTransaction().commit();

addEntity()示例

session.beginTransaction();
String sql = "select id,username,userpwd from t_user";
// addEntity()可以告訴Hibernate你想要封裝成對象的類型，然后自動為你封裝
SQLQuery query = session.createSQLQuery(sql).addEntity(User.class);
List<User> list = query.list();
for(User user : list){
System.out.println(user.getUserName());
}
session.getTransaction().commit();

uniqueResult示例

session.beginTransaction();
String sql = "select id,username,userpwd from t_user where id = 2";
SQLQuery query = session.createSQLQuery(sql).addEntity(User.class);
User user = (User) query.uniqueResult();
System.out.println(user.getUserName());
session.getTransaction().commit();

以上就是關于“Hibernate查詢的幾種方式”的介紹，大家如果想了解更多相關知識，不妨來關注一下動力節點的Hibernate視頻教程，教程內容細致全面，通俗易懂，適合小白學習，希望對大家能夠有所幫助。