八、hibernate的查询（HQL）

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

package com.qf.entity;

import java.util.HashSet;
import java.util.Set;

public class Parent {

    private Long pid;
    private String pname;
    private Integer age;
    private Set<Children> childs = new HashSet<>();
    
    @Override
    public String toString() {
        return "Parent [pid=" + pid + ", pname=" + pname + ", age=" + age + "]";
    }
    
    public Long getPid() {
        return pid;
    }
    public void setPid(Long pid) {
        this.pid = pid;
    }
    public String getPname() {
        return pname;
    }
    public void setPname(String pname) {
        this.pname = pname;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public Set<Children> getChilds() {
        return childs;
    }
    public void setChilds(Set<Children> childs) {
        this.childs = childs;
    }
    
}

2.Children.java

package com.qf.entity;

public class Children {

    private Long cid;
    private String cname;
    private Character sex;
    private Parent p;
    
    @Override
    public String toString() {
        return "Children [cid=" + cid + ", cname=" + cname + ", sex=" + sex + ", p=" + p + "]";
    }
    
    public Long getCid() {
        return cid;
    }
    public void setCid(Long cid) {
        this.cid = cid;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public Character getSex() {
        return sex;
    }
    public void setSex(Character sex) {
        this.sex = sex;
    }
    public Parent getP() {
        return p;
    }
    public void setP(Parent p) {
        this.p = p;
    }
}

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