HQL简单用法

总共涉及到四个类：

 

(1)Category.java

package edu.smc.hibernate;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
@Entity
public class Category {
	private int id;
	private String name;
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

(2)Topic.java

package edu.smc.hibernate;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entity
public class Topic {
	private int id;
	private String title;
	private Category category;
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
	public Category getCategory() {
		return category;
	}
	public void setCategory(Category category) {
		this.category = category;
	}
	public void setId(int id) {
		this.id = id;
	}
    @ManyToOne
	public Category getCatetory() {
		return category;
	}
	public void setCatetory(Category catetory) {
		this.category = category;
	}
}

(3)Msg.java

package edu.smc.hibernate;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entity
public class Msg {
	private int id;
	private String cont;
	public String getCont() {
		return cont;
	}
	public void setCont(String cont) {
		this.cont = cont;
	}
	private Topic topic;
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	
	@ManyToOne
	public Topic getTopic() {
		return topic;
	}
	public void setTopic(Topic topic) {
		this.topic = topic;
	}
	
}

(4)MsgInfo.java

 

package edu.smc.hibernate;
public class MsgInfo {
	private int id;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getCont() {
		return cont;
	}
	public void setCont(String cont) {
		this.cont = cont;
	}
	public String getTopicName() {
		return topicName;
	}
	public void setTopicName(String topicName) {
		this.topicName = topicName;
	}
	public String getCategoryName() {
		return categoryName;
	}
	public void setCategoryName(String categoryName) {
		this.categoryName = categoryName;
	}
	private String cont;
	private String topicName;
	private String categoryName;
	public MsgInfo(int id,String cont,String topicName,String categoryName){
		this.id=id;
		this.cont=cont;
		this.topicName=topicName;
		this.categoryName=categoryName;
	}
	
}

1.取出所有的Category对象 .

	         Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Category");
		List categories = (List)q.list();
		for(Category c : categories) {
			System.out.println(c.getName());
		}
		session.getTransaction().commit();
		session.close();

2.取出Category.name>c5 的对象

 

                  Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Category c where c.name > 'c5'");
		List categories = (List)q.list();
		for(Category c : categories) {
			System.out.println(c.getName());
		}
		session.getTransaction().commit();
		session.close();

3.取出所有Category对象，并用Category.name进行倒序排序

	   Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Category c order by c.name desc");
		List categories = (List)q.list();
		for(Category c : categories) {
			System.out.println(c.getName());
		}
		session.getTransaction().commit();
		session.close();

4.取出id大约参数min并且小于参数max的Category对象

 

 

                  Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Category c where c.id > :min and c.id < :max")
			.setInteger("min", 2)
			.setInteger("max", 8);
		List categories = (List)q.list();
		for(Category c : categories) {
			System.out.println(c.getId() + "-" + c.getName());
		}
		session.getTransaction().commit();
		session.close();

5.取出id在某两个数之间的Category对象（预处理方式）

Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Category c where c.id > ? and c.id < ?");
		q.setParameter(0, 2)
			.setParameter(1, 8);

		List categories = (List)q.list();
		for(Category c : categories) {
			System.out.println(c.getId() + "-" + c.getName());
		}
		session.getTransaction().commit();
		session.close();

6.分页

	         Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Category c order by c.name desc");
		q.setMaxResults(4);  /*设置每页最多的记录数*/
		q.setFirstResult(2);/*设置从那一条记录开始取*/
		List categories = (List)q.list();
		for(Category c : categories) {
			System.out.println(c.getId() + "-" + c.getName());
		}
		session.getTransaction().commit();
		session.close();

7.值取出 Category对象的 name,id 并且按照name进行降序排序

                  Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("select c.id,  c.name from Category c order by c.name desc");
		List categories = (List)q.list();
		for(Object[] o : categories) {
			System.out.println(o[0] + "-" + o[1]);
		}
		session.getTransaction().commit();
		session.close();

8.取出Catetory id为1的Topic对象

Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Topic t where t.category.id = 1");
		List topics = (List)q.list();
		for(Topic t : topics) {
			System.out.println(t.getTitle());
		}
		session.getTransaction().commit();
		session.close();

9.取出Category id为1的 Topic下的Msg对象

	Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Msg m where m.topic.category.id = 1");
		
		for(Object o : q.list()) {
			Msg m = (Msg)o;
			System.out.println(m.getCont());
		}
		session.getTransaction().commit();
		session.close();

10.取出一些数据组成一个新的对象（VO,DTO）

	Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("select new edu.smc.hibernate.MsgInfo(m.id, m.cont, m.topic.title,              m.topic.category.name) from Msg");
		
		for(Object o : q.list()) {
			MsgInfo m = (MsgInfo)o;
			System.out.println(m.getCont());
		}
		session.getTransaction().commit();
		session.close();

11.Join的写法

                  Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("select t.title, c.name from Topic t join t.category c "); 
		/** 不能直接写Category名，而必须写t.category,因为有可能存在多个成员变量（属于一个类），需要指明用哪一个成员变量的连接条件来做连接*/
		for(Object o : q.list()) {
			Object[] m = (Object[])o;
			System.out.println(m[0] + "-" + m[1]);
		}
		session.getTransaction().commit();
		session.close();

12.使用uniqueResult方法（当确定返回的实例只有一个或者null时 用uniqueResult()方法）

		Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Msg m where m = :MsgToSearch "); /*这里是对象相等*/
		Msg m = new Msg();
		m.setId(1);
		q.setParameter("MsgToSearch", m);      /*设置参数为 Msg对象*/
		Msg mResult = (Msg)q.uniqueResult();   /*使用 Query 的 uniqueResult()方法*/
		System.out.println(mResult.getCont());
		session.getTransaction().commit();
		session.close();

13 .获取总个数

 

	         Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("select count(*) from Msg m");
		
		long count = (Long)q.uniqueResult();
		System.out.println(count);
		session.getTransaction().commit();
		session.close();

14.max , min ,avg, sum的用法

                  Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("select max(m.id), min(m.id), avg(m.id), sum(m.id) from Msg m");
		Object[] o = (Object[])q.uniqueResult();
		System.out.println(o[0] + "-" + o[1] + "-" + o[2] + "-" + o[3]);
		session.getTransaction().commit();
		session.close();

15. between....and

                  Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Msg m where m.id between 3 and 5");
		
		for(Object o : q.list()) {
			Msg m = (Msg)o;
			System.out.println(m.getId() + "-" + m.getCont());
		}
		session.getTransaction().commit();
		session.close();

16.集合的用法

	         Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Msg m where m.id in (3,4, 5)");
		
		for(Object o : q.list()) {
			Msg m = (Msg)o;
			System.out.println(m.getId() + "-" + m.getCont());
		}
		session.getTransaction().commit();
		session.close();

17. is not null

                  Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Msg m where m.cont is not null");
		
		for(Object o : q.list()) {
			Msg m = (Msg)o;
			System.out.println(m.getId() + "-" + m.getCont());
		}
		session.getTransaction().commit();
		session.close();

18.empty

                  Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Topic t where t.msgs is empty");
		
		for(Object o : q.list()) {
			Topic t = (Topic)o;
			System.out.println(t.getId() + "-" + t.getTitle());
		}
		session.getTransaction().commit();
		session.close();

19.like( % 代表一个或多个，_ 代表一个)

	         Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Topic t where t.title like '%5'");
		
		for(Object o : q.list()) {
			Topic t = (Topic)o;
			System.out.println(t.getId() + "-" + t.getTitle());
		}
		session.getTransaction().commit();
		session.close();

                  Session session = sf.openSession();
                  session.beginTransaction();
                  Query q = session.createQuery("from Topic t where t.title like '_5'");
  
                 for(Object o : q.list()) {
                 Topic t = (Topic)o;
                 System.out.println(t.getId() + "-" + t.getTitle());
                 }
                 session.getTransaction().commit();
                session.close();

20.内置函数（不常用）

Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("select lower(t.title)," +
					          "upper(t.title)," +
						  "trim(t.title)," +
					  "concat(t.title, '***')," +
						 "length(t.title)" +
						" from Topic t ");
		
		for(Object o : q.list()) {
			Object[] arr = (Object[])o;
			System.out.println(arr[0] + "-" + arr[1] + "-" + arr[2] + "-" + arr[3] + "-" + arr[4] + "-");
		}
		session.getTransaction().commit();
		session.close();

                  Session session = sf.openSession();
                session.beginTransaction();
                Query q = session.createQuery("select abs(t.id)," +
                "sqrt(t.id)," +
                "mod(t.id, 2)" +
                " from Topic t ");
  
                for(Object o : q.list()) {
                 Object[] arr = (Object[])o;
                   System.out.println(arr[0] + "-" + arr[1] + "-" + arr[2] );
                }
               session.getTransaction().commit();
               session.close();

               Session session = sf.openSession();      /*日期，时间，时间戳*/
               session.beginTransaction();
               Query q = session.createQuery("select current_date, current_time, current_timestamp, t.id from Topic t");
  
               for(Object o : q.list()) {
               Object[] arr = (Object[])o;
                System.out.println(arr[0] + " | " + arr[1] + " | " + arr[2] + " | " + arr[3]);
               }
               session.getTransaction().commit();
               session.close();

21.日期比较

Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Topic t where t.createDate < :date");
		q.setParameter("date", new Date());
		for(Object o : q.list()) {
			Topic t = (Topic)o;
			System.out.println(t.getTitle());
		}
		session.getTransaction().commit();
		session.close();

22.分组 Having

               Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("select t.title, count(*) from Topic t group by t.title having count(*) >= 1") ;
		for(Object o : q.list()) {
			Object[] arr = (Object[])o;
			System.out.println(arr[0] + "|" + arr[1]);
		}
		session.getTransaction().commit();
		session.close();

23.子查询

	     Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Topic t where t.id < (select avg(t.id) from Topic t)") ;
		for(Object o : q.list()) {
			Topic t = (Topic)o;
			System.out.println(t.getTitle());
		}
		session.getTransaction().commit();
		session.close();

24.关键字ALL的使用

               Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("from Topic t where t.id < ALL (select t.id from Topic t where mod(t.id, 2)= 0) ") ;
		for(Object o : q.list()) {
			Topic t = (Topic)o;
			System.out.println(t.getTitle());
		}
		session.getTransaction().commit();
		session.close();

25.Exist(可用in实现exist的功能，exist的效率更高，所以一般选用exist)

              Session session = sf.openSession();
		session.beginTransaction();// t.id not in (1)
		Query q = session.createQuery("from Topic t where not exists (select m.id from Msg m where m.topic.id=t.id)") ;
//		Query q = session.createQuery("from Topic t where exists (select m.id from Msg m where m.topic.id=t.id)") ;
		for(Object o : q.list()) {
			Topic t = (Topic)o;
			System.out.println(t.getTitle());
		}
		session.getTransaction().commit();
		session.close();

26.更新

               Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.createQuery("update Topic t set t.title = upper(t.title)") ;
		
		q.executeUpdate();
		q = session.createQuery("from Topic");
		for(Object o : q.list()) {
			Topic t = (Topic)o;
			System.out.println(t.getTitle());
		}
		session.createQuery("update Topic t set t.title = lower(t.title)")
			.executeUpdate();
		session.getTransaction().commit();
		session.close();

27.命名查询（便于集中管理）

在类中写

@NamedQueries(
  {
   @NamedQuery(name="topic.selectCertainTopic", query="from Topic t where t.id = :id")
  }
  )

               Session session = sf.openSession();
		session.beginTransaction();
		Query q = session.getNamedQuery("topic.selectCertainTopic");
		q.setParameter("id", 5);
		Topic t = (Topic)q.uniqueResult();
		System.out.println(t.getTitle());
		session.getTransaction().commit();
		session.close();

28.Native SQL

                Session session = sf.openSession();
		session.beginTransaction();
		SQLQuery q = session.createSQLQuery("select * from category limit 2,4").addEntity(Category.class);
		List categories = (List)q.list();
		for(Category c : categories) {
			System.out.println(c.getName());
		}
		session.getTransaction().commit();
		session.close();

 

 

注：HQL 应该和导航相结合，共同为查询提供服务。