HQL：Hibernate Query Language
- 提供更加丰富灵活、更为强大的查询能力
- HQL更接近SQL语句查询语法
- 面向对象的查询
- "from Children where cid<?" ：这里Children指的是类不是children表；cid指的是Children类中的对象而不是children表中的字段
HQL查询（单表）
以一对多关系映射为例（parent[1]<——>children[n]）
简单查询
实体类
1.Parent.java
1 package com.qf.entity; 2 3 import java.util.HashSet; 4 import java.util.Set; 5 6 public class Parent { 7 8 private Long pid; 9 private String pname; 10 private Integer age; 11 private Set<Children> childs = new HashSet<>(); 12 13 @Override 14 public String toString() { 15 return "Parent [pid=" + pid + ", pname=" + pname + ", age=" + age + "]"; 16 } 17 18 public Long getPid() { 19 return pid; 20 } 21 public void setPid(Long pid) { 22 this.pid = pid; 23 } 24 public String getPname() { 25 return pname; 26 } 27 public void setPname(String pname) { 28 this.pname = pname; 29 } 30 public Integer getAge() { 31 return age; 32 } 33 public void setAge(Integer age) { 34 this.age = age; 35 } 36 public Set<Children> getChilds() { 37 return childs; 38 } 39 public void setChilds(Set<Children> childs) { 40 this.childs = childs; 41 } 42 43 }
2.Children.java
1 package com.qf.entity; 2 3 public class Children { 4 5 private Long cid; 6 private String cname; 7 private Character sex; 8 private Parent p; 9 10 @Override 11 public String toString() { 12 return "Children [cid=" + cid + ", cname=" + cname + ", sex=" + sex + ", p=" + p + "]"; 13 } 14 15 public Long getCid() { 16 return cid; 17 } 18 public void setCid(Long cid) { 19 this.cid = cid; 20 } 21 public String getCname() { 22 return cname; 23 } 24 public void setCname(String cname) { 25 this.cname = cname; 26 } 27 public Character getSex() { 28 return sex; 29 } 30 public void setSex(Character sex) { 31 this.sex = sex; 32 } 33 public Parent getP() { 34 return p; 35 } 36 public void setP(Parent p) { 37 this.p = p; 38 } 39 }
注：两个实体类的toString()方法重写时
- Parent类的toString()方法如果包含Set<Children>的属性，那么Children类的toString()方法就不能包含Parent的属性，否则查询输出对象信息时会陷入死循环，导致StackOverflowError
package com.qf.util;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtils {
private static Configuration cfg ;
private static SessionFactory factory;
static {
cfg = new Configuration().configure();
factory = cfg.buildSessionFactory();
}
public static Session getCurrentSession() {
return factory.getCurrentSession();
}
}
@Test
/**
* HQL简单查询
*/
public void queryByHQL() {
Session session = HibernateUtils.getCurrentSession();
Transaction tx = session.beginTransaction();
Query query = session.createQuery("from Children");
List<Children> list = query.list();
for (Children children : list) {
System.out.println(children);
}
tx.commit();
}
别名查询
String hql = "select c from Children c order by cid desc";
HQL中支持数据库的带有别名的查询
@Test
/**
* HQL别名查询
*/
public void queryByHQL02() {
Session session = HibernateUtils.getCurrentSession();
Transaction tx = session.beginTransaction();
// String hql = "select c from Children c";
String hql = "select c from Children c order by cid desc";
Query query = session.createQuery(hql);
List<Children> list = query.list();
for (Children children : list) {
System.out.println(children);
}
tx.commit();
}
条件查询
参数绑定
- 位置绑定
String hql = "select c from Children c where cid<? and cname like ?"; Query query = session.createQuery(hql); query.setParameter(0, 20L); query.setParameter(1, "%张%");
- hql中参数以"？"代替
- 索引从0开始
- 名称绑定
String hql = "select c from Children c where cid<:aaa and cname like :bbb"; Query query = session.createQuery(hql); query.setParameter("aaa", 20L); query.setParameter("bbb", "%张%");
- hql中参数以 ":自定义名称"的形式代替
- 不使用索引，使用（名称，值）的形式
@Test
/**
* HQL条件查询
*/
public void queryByHQL03() {
Session session = HibernateUtils.getCurrentSession();
Transaction tx = session.beginTransaction();
/*//一个条件（位置绑定）
String hql = "select c from Children c where cid<?";
Query query = session.createQuery(hql);
query.setInteger(0, 3);*/
//多个条件（位置绑定）
/*String hql = "select c from Children c where cid<? and cname like ?";
Query query = session.createQuery(hql);
query.setParameter(0, 20L);
query.setParameter(1, "%张%");*/
//多个条件（名称绑定）
String hql = "select c from Children c where cid<:aaa and cname like :bbb";
Query query = session.createQuery(hql);
query.setParameter("aaa", 20L);
query.setParameter("bbb", "%张%");
List<Children> list = query.list();
for (Children children : list) {
System.out.println(children);
}
tx.commit();
}
投影查询
查询表中部分字段
方式一：返回Object[ ]
@Test
/**
* HQL简单查询
*/
public void queryByHQL() {
Session session = HibernateUtils.getCurrentSession();
Transaction tx = session.beginTransaction();
Query query = session.createQuery("select cname,sex from Children");
List<Object[]> list = query.list();
for (Object[] objs : list) {
System.out.println(Arrays.toString(objs));
}
tx.commit();
}
方式二：返回实体类对象
实体类
- 添加无参构造方法
- 添加有参构造方法（构造方法参数是你所要查询的属性）
package com.qf.entity;
public class Children {
private Long cid;
private String cname;
private Character sex;
private Parent p;
public Children(String cname, Character sex) {
super();
this.cname = cname;
this.sex = sex;
}
public Children() {
super();
}
......
}
测试方法
@Test
/**
* HQL简单查询
*/
public void queryByHQL() {
Session session = HibernateUtils.getCurrentSession();
Transaction tx = session.beginTransaction();
Query query = session.createQuery("select new Children(cname,sex) from Children");
List<Children> list = query.list();
for (Children children : list) {
System.out.println(children);
}
tx.commit();
}
分页查询
- query.setFirstResult(int start)：从第几条记录开始查询
- query.setMaxResults(int num)：本页一共查询多少条记录
@Test
public void query() {
Session session = HibernateUtils.getCurrentSession();
Transaction tx = session.beginTransaction();
String sql = "from Children";
Query query = session.createQuery(sql);
query.setFirstResult(2);
query.setMaxResults(3);
List<Children> list = query.list();
for (Children c : list) {
System.out.println(c);
}
tx.commit();
}
分组查询
max()、min()、count()、sum()、avg()
Object obj = query.uniqueResult()：返回唯一结果
@Test
/**
* HQL简单查询
*/
public void queryByHQL() {
Session session = HibernateUtils.getCurrentSession();
Transaction tx = session.beginTransaction();
Query query = session.createQuery("select pid,pname,count(*) from Parent group by pid");
List<Object[]> list = query.list();
for (Object[] objects : list) {
System.out.println(Arrays.toString(objects));
}
tx.commit();
}
HQL查询（多表）
内连接查询
正常的内连接sql：select * from Children c inner join Parent p
HQL："from Children c inner join c.p "
- 其中c.p是Children类的Parent属性变量p
- 返回的是对象数组
package com.qf.entity;
public class Children {
private Long cid;
private String cname;
private Character sex;
private Parent p;
....
}
@Test
/**
* HQL简单查询
*/
public void queryByHQL() {
Session session = HibernateUtils.getCurrentSession();
Transaction tx = session.beginTransaction();
Query query = session.createQuery("from Children c inner join c.p ");
List<Object[]> list = query.list();
for (Object[] objects : list) {
System.out.println(Arrays.toString(objects));
}
tx.commit();
}
------------------------------console-------------------------------
[Children [cid=1, cname=张三8, sex=1, p=Parent [pid=1, pname=老张, age=45]], Parent [pid=1, pname=老张, age=45]] [Children [cid=2, cname=张三0, sex=0, p=Parent [pid=1, pname=老张, age=45]], Parent [pid=1, pname=老张, age=45]] [Children [cid=3, cname=张三2, sex=1, p=Parent [pid=1, pname=老张, age=45]], Parent [pid=1, pname=老张, age=45]] ............... [Children [cid=28, cname=王五0, sex=0, p=Parent [pid=3, pname=老王, age=43]], Parent [pid=3, pname=老王, age=43]] [Children [cid=29, cname=王五8, sex=0, p=Parent [pid=3, pname=老王, age=43]], Parent [pid=3, pname=老王, age=43]] [Children [cid=30, cname=王五6, sex=1, p=Parent [pid=3, pname=老王, age=43]], Parent [pid=3, pname=老王, age=43]]
迫切内连接
Query query = session.createQuery("from Children c inner join fetch c.p ");
- 普通内连接HQL的inner join后加上fetch即可
- 效果：返回的是内连接的左边对象（该例中Parent作为Children属性）
@Test
/**
* HQL简单查询
*/
public void queryByHQL() {
Session session = HibernateUtils.getCurrentSession();
Transaction tx = session.beginTransaction();
Query query = session.createQuery("from Children c inner join fetch c.p ");
List<Children> list = query.list();
for (Children c : list) {
System.out.println(c);
}
tx.commit();
}
------------------------------console-------------------------------
Children [cid=1, cname=张三8, sex=1, p=Parent [pid=1, pname=老张, age=45]] Children [cid=2, cname=张三0, sex=0, p=Parent [pid=1, pname=老张, age=45]] Children [cid=3, cname=张三2, sex=1, p=Parent [pid=1, pname=老张, age=45]] .................... Children [cid=28, cname=王五0, sex=0, p=Parent [pid=3, pname=老王, age=43]] Children [cid=29, cname=王五8, sex=0, p=Parent [pid=3, pname=老王, age=43]] Children [cid=30, cname=王五6, sex=1, p=Parent [pid=3, pname=老王, age=43]]
左外连接、右外连接（没有迫切右外连接）以及迫切左外连接使用也类似