Hibernate的基本策略查询。
创建pojo.User 类
package com.pojo;
import java.util.HashSet;
import java.util.Set;
/**
* User entity. @author MyEclipse Persistence Tools
*/
public class User implements java.io.Serializable {
// Fields
private String username;
private String password;
private Set goodses = new HashSet(0);
// Constructors
/** default constructor */
public User() {
}
/** minimal constructor */
public User(String username, String password) {
this.username = username;
this.password = password;
}
/** full constructor */
public User(String username, String password, Set goodses) {
this.username = username;
this.password = password;
this.goodses = goodses;
}
// Property accessors
public String getUsername() {
return this.username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return this.password;
}
public void setPassword(String password) {
this.password = password;
}
public Set getGoodses() {
return this.goodses;
}
public void setGoodses(Set goodses) {
this.goodses = goodses;
}
}
一、投影查询
@org.junit.Test
public void testTouying(){
Session session = HibernateSessionFactory.getSession();
String hql = "select username ,password from User" ;
Query query = session.createQuery(hql);
List<Object[]> list = query.list();
for (Object[] objects : list) {
System.out.println(objects[0]+"\t"+objects[1]);
}
}
@org.junit.Test
public void testTouying2(){
Session session = HibernateSessionFactory.getSession();
String hql = "select new User(username,password) from User" ;
Query query = session.createQuery(hql);
List<User> list = query.list();
for (User user : list) {
System.out.println(user.getUsername()+"\t"+user.getPassword());
}
}
上面有两种投影查询。一般使用第二种。
二、条件查询
@org.junit.Test
public void testFZ(){
Session session = HibernateSessionFactory.getSession() ;
String hql = "from User where username = ?" ;
Query query = session.createQuery(hql) ;
query.setParameter(0, "刘强") ;
List<User> list = query.list() ;
for (User user : list) {
System.out.println(user.getUsername()+"\t"+user.getPassword()) ;
}
}
条件查询和sql 类似，但是hql面向的是对象。
三、分页查询
@org.junit.Test
public void testFenye(){
Session session = HibernateSessionFactory.getSession();
String hql = "from User" ;
Query createQuery = session.createQuery(hql);
createQuery.setFirstResult(0).setMaxResults(3);
List<User> list = createQuery.list();
for (User user : list) {
System.out.println(user.getUsername());
}
}
由于Hibernate不能通用得到页码和数量，所以Hibernate封装了mysql中的limit，setFirstResult()从那个开始，setMaxResults()得到多少个结果。
四、迫切查询（多表查询）
@org.junit.Test
public void testPoQie(){
Session session = HibernateSessionFactory.getSession();
String hql = "from User u join u.goodses" ;
Query query = session.createQuery(hql);
List<Object[]> list = query.list() ;
for (Object[] objects : list) {
System.out.println(objects[0]+"\t"+objects[1]);
}
}
@org.junit.Test
public void testPoQie2(){
Session session = HibernateSessionFactory.getSession();
String hql = "from User u join fetch u.goodses" ;
Query query = session.createQuery(hql);
List<User> list = query.list() ;
for (User user : list) {
System.out.println(user.getUsername()+"\t"+user.getPassword()+"\t"+user.getGoodses());
}
}
通常用第二种。
