Hibernate HQL示例一:基本配置及测试查询

最新推荐文章于 2020-05-11 02:13:03 发布

luweifeng1983

最新推荐文章于 2020-05-11 02:13:03 发布

阅读量312

点赞数

分类专栏： Hibernate 文章标签： Hibernate MySQL XML 数据结构 JDBC

Hibernate 专栏收录该内容

45 篇文章

订阅专栏

本文介绍Hibernate HQL查询的基础用法，包括基本语法、表别名的使用等，并通过具体示例展示了如何在Java程序中执行HQL查询。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

Hibernate Hql查询：

大小写敏感，如：from Student 指的是从Student对象中查询。

示例：

第一步创建数据库hibernate

第二步运行ExportDB.java生成表结构。

第三步运行InitData.java生成数据。

第四步进行其它测试。

工具类代码：

package com.bjsxt.hibernate;

import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;

public class ExportDB {

	public static void main(String[] args) {
		
		//读取配置文件
		Configuration cfg = new Configuration().configure();
		
		//创建SchemaExport对象
		SchemaExport export = new SchemaExport(cfg);
		
		//创建数据库表
		export.create(true,true);
	}

}

package com.bjsxt.hibernate;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtils {
	
	private static SessionFactory factory;
	
	private HibernateUtils() {}
	
	static {
		Configuration cfg = new Configuration().configure();
		factory = cfg.buildSessionFactory();
	}
	
	public static SessionFactory getSessionFactory() {
		return factory;
	}
	
	public static Session getSession() {
		return factory.openSession();
	}
	
	public static void closeSession(Session session) {
		if (session != null) {
			if (session.isOpen()) {
				session.close();
			}
		}
	}
	
}

package com.bjsxt.hibernate;

import java.util.Set;

public class Classes {
	
	private int id;
	
	private String name;
	
	private Set students;
	
	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;
	}

	public Set getStudents() {
		return students;
	}

	public void setStudents(Set students) {
		this.students = students;
	}
	
	
}

package com.bjsxt.hibernate;

import java.util.Date;

public class Student {
	
	private int id;
	
	private String name;
	
    private Date createTime;	
	
	private Classes classes;
	
	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;
	}

	public Classes getClasses() {
		return classes;
	}

	public void setClasses(Classes classes) {
		this.classes = classes;
	}

	public Date getCreateTime() {
		return createTime;
	}

	public void setCreateTime(Date createTime) {
		this.createTime = createTime;
	}
}

Classes.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.bjsxt.hibernate.Classes" table="t_classes">
		<id name="id">
			<generator class="native"/>
		</id>
		<property name="name"/>
		<!-- 
			<set name="students" cascade="all" order-by="id">
		 -->
		 <set name="students" inverse="true">
			<key column="classid"/>
			<one-to-many class="com.bjsxt.hibernate.Student"/>
		</set>
	</class>
</hibernate-mapping>

Student.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.bjsxt.hibernate.Student" table="t_student">
		<id name="id">
			<generator class="native"/>
		</id>
		<property name="name"/>
		<property name="createTime"/>
		<many-to-one name="classes" column="classid"/>
		<filter name="idfilter" condition="id &lt; :myid"/>
	</class>
	<query name="searchStudents"><![CDATA[
		select s from Student s where s.id < ?
	]]>
	</query>
	<filter-def name="idfilter">
		<filter-param name="myid" type="integer"/>
	</filter-def>
</hibernate-mapping>

hibernate.cfg.xml

<!DOCTYPE hibernate-configuration PUBLIC
	"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
	<session-factory>
		<property name="hibernate.connection.url">
			jdbc:mysql://127.0.0.1/hibernate
		</property>
		<property name="hibernate.connection.driver_class">
			com.mysql.jdbc.Driver
		</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password">super</property>
		<property name="dialect">
			org.hibernate.dialect.MySQLDialect
		</property>
		<property name="show_sql">true</property>
		
		<mapping resource="com/bjsxt/hibernate/Classes.hbm.xml"/>
		<mapping resource="com/bjsxt/hibernate/Student.hbm.xml"/>
	</session-factory>
</hibernate-configuration>

上面文件创建完成之后，运行ExportDB.java

数据库中创建两个表格：t_classes,t_student

表结构如下：

mysql> desc t_classes;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | int(11)      | NO   | PRI | NULL    | auto_increment |
| name  | varchar(255) | YES  |     | NULL    |                |
+-------+--------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

mysql> desc t_student;
+------------+--------------+------+-----+---------+----------------+
| Field      | Type         | Null | Key | Default | Extra          |
+------------+--------------+------+-----+---------+----------------+
| id         | int(11)      | NO   | PRI | NULL    | auto_increment |
| name       | varchar(255) | YES  |     | NULL    |                |
| createTime | datetime     | YES  |     | NULL    |                |
| classid    | int(11)      | YES  | MUL | NULL    |                |
+------------+--------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

为了作测试生成数据类InitData.java如下：

package com.bjsxt.hibernate;

import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;

public class InitData {

	public static void main(String[] args) {
			Session session = HibernateUtils.getSession();

			try {
				session.beginTransaction();

				for(int i=0; i<10; i++){
				
					Classes classes = new Classes();
					classes.setName("班级"+i);
					session.save(classes);
					
					for(int j=0; j<10; j++){
						Student student = new Student();
						student.setName("班级"+i+"的学生"+j);
						student.setCreateTime(randomDate("2007-01-01","2007-03-01"));
						
						//在内存中建立由student指向classes的引用
						student.setClasses(classes);
						session.save(student);
					}
				}
				
				for(int i=0; i<5; i++){
					Classes classes = new Classes();
					classes.setName("无学生班级"+i);
					session.save(classes);
				}
				
				for(int i=0; i<10; i++){
					Student student = new Student();
					student.setName("无业游民"+i);
					session.save(student);
				}
				
				session.getTransaction().commit();
			} catch (Exception e) {
				e.printStackTrace();
				session.getTransaction().rollback();
			} finally{
				HibernateUtils.closeSession(session);
			}
		}	
		
		/**
		 * 获取随机日期
		 * @param beginDate 起始日期，格式为：yyyy-MM-dd
		 * @param endDate 结束日期，格式为：yyyy-MM-dd
		 * @return
		 */
		private static Date randomDate(String beginDate,String endDate){
			try {
				SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
				Date start = format.parse(beginDate);
				Date end = format.parse(endDate);
				
				if(start.getTime() >= end.getTime()){
					return null;
				}
				
				long date = random(start.getTime(),end.getTime());
				
				return new Date(date);
			} catch (Exception e) {
				e.printStackTrace();
			}
			return null;
		}
		
		private static long random(long begin,long end){
			long rtn = begin + (long)(Math.random() * (end - begin));
			if(rtn == begin || rtn == end){
				return random(begin,end);
			}
			return rtn;
		}
}

以下开始做测试：

测试类1：SimpleObjectQueryTest.java

package com.bjsxt.hibernate;

import java.util.Iterator;
import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;

import junit.framework.TestCase;

/**
 * 对象查询的基本测试
 * @author Administrator
 *
 */
public class SimpleObjectQueryTest extends TestCase {
	
	public void testQuery1() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			
			//可以忽略select语句
			List students = session.createQuery("from Student").list();
			for (Iterator iter = students.iterator();iter.hasNext();) {
				
				//返回值是Student对象
				Student student = (Student)iter.next();
				System.out.println(student.getName());
			}
		}catch(Exception e) {
			e.printStackTrace();
		}finally {
			HibernateUtils.closeSession(session);
		}	
	}

	public void testQuery2() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			
			//可以忽略select语句,表可以加别名
			List students = session.createQuery("from Student s").list();
			for (Iterator iter = students.iterator();iter.hasNext();) {
				
				//返回值是Student对象
				Student student = (Student)iter.next();
				System.out.println(student.getName());
			}
		}catch(Exception e) {
			e.printStackTrace();
		}finally {
			HibernateUtils.closeSession(session);
		}	
	}

	public void testQuery3() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			
			//可以忽略select语句,表可以加别名
			List students = session.createQuery("from Student as s").list();
			for (Iterator iter = students.iterator();iter.hasNext();) {
				
				//返回值是Student对象
				Student student = (Student)iter.next();
				System.out.println(student.getName());
			}
		}catch(Exception e) {
			e.printStackTrace();
		}finally {
			HibernateUtils.closeSession(session);
		}	
	}

	public void testQuery4() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			
			//使用select关键字时，必须定义别名
			List students = session.createQuery("select s from Student s").list();
			for (Iterator iter = students.iterator();iter.hasNext();) {
				
				//返回值是Student对象
				Student student = (Student)iter.next();
				System.out.println(student.getName());
			}
		}catch(Exception e) {
			e.printStackTrace();
		}finally {
			HibernateUtils.closeSession(session);
		}	
	}

	public void testQuery5() {
		Session session = null;
		try {
			session = HibernateUtils.getSession();
			
			//不支持select * ....这样的HQL查询语句
			List students = session.createQuery("select * from Student").list();
			for (Iterator iter = students.iterator();iter.hasNext();) {
				
				//返回值是Student对象
				Student student = (Student)iter.next();
				System.out.println(student.getName());
			}
		}catch(Exception e) {
			e.printStackTrace();
		}finally {
			HibernateUtils.closeSession(session);
		}	
	}
}

上面测试中得到的结论：

做查询时，可以忽略select语句；
表可以加别名；
使用select关键字时，必须定义别名；
不支持select * ....这样的HQL查询语句