hibernate框架学习笔记10：HQL查询详解

HQL语句中不可以出现与表有关的内容，而是对象的属性

实体类（注意配置文件）：

package domain;

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

//客户实体
public class Customer {

    private Long cust_id;
    private String cust_name;
    private String cust_source;
    private String cust_industry;
    private String cust_level;
    private String cust_linkman;
    private String cust_phone;
    private String cust_mobile;
    //使用set集合,表达一对多关系
    private Set<LinkMan> linkMens = new HashSet<LinkMan>();

    public Set<LinkMan> getLinkMens() {
        return linkMens;
    }
    public void setLinkMens(Set<LinkMan> linkMens) {
        this.linkMens = linkMens;
    }
    public Long getCust_id() {
        return cust_id;
    }
    public void setCust_id(Long cust_id) {
        this.cust_id = cust_id;
    }
    public String getCust_name() {
        return cust_name;
    }
    public void setCust_name(String cust_name) {
        this.cust_name = cust_name;
    }
    public String getCust_source() {
        return cust_source;
    }
    public void setCust_source(String cust_source) {
        this.cust_source = cust_source;
    }
    public String getCust_industry() {
        return cust_industry;
    }
    public void setCust_industry(String cust_industry) {
        this.cust_industry = cust_industry;
    }
    public String getCust_level() {
        return cust_level;
    }
    public void setCust_level(String cust_level) {
        this.cust_level = cust_level;
    }
    public String getCust_linkman() {
        return cust_linkman;
    }
    public void setCust_linkman(String cust_linkman) {
        this.cust_linkman = cust_linkman;
    }
    public String getCust_phone() {
        return cust_phone;
    }
    public void setCust_phone(String cust_phone) {
        this.cust_phone = cust_phone;
    }
    public String getCust_mobile() {
        return cust_mobile;
    }
    public void setCust_mobile(String cust_mobile) {
        this.cust_mobile = cust_mobile;
    }
    @Override
    public String toString() {
        return "Customer [cust_id=" + cust_id + ", cust_name=" + cust_name + "]";
    }
}

抽取工具类：

package utils;

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

public class HibernateUtils {
    private static SessionFactory sf;

    static{
        //1 创建,调用空参构造
        Configuration conf = new Configuration().configure();
        //2 根据配置信息,创建 SessionFactory对象
         sf = conf.buildSessionFactory();
    }

    //获得session => 获得全新session
    public static Session openSession(){
                //3 获得session
                Session session = sf.openSession();

                return session;

    }
    //获得session => 获得与线程绑定的session
    public static Session getCurrentSession(){
        //3 获得session
        Session session = sf.getCurrentSession();

        return session;
    }
}

测试类：

基本语法：

package hql;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import domain.Customer;
import utils.HibernateUtils;

//学习HQL语法
public class Demo {

    //基本语法
    @Test
    public void fun1(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql = " from  domain.Customer ";//完整写法
        String hql2 = " from  Customer "; //简单写法
        String hql3 = " from java.lang.Object "; //查询所有Object对象，即所有对象

        Query query = session.createQuery(hql);

        List list = query.list();

        System.out.println(list);
        //----------------------------------------------------
        tx.commit();
        session.close();

    }

    @Test
    //排序
    public void fun2(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql1 = " from  domain.Customer order by cust_id asc ";//完整写法升序
        String hql2 = " from  domain.Customer order by cust_id desc ";//完整写法降序

        Query query = session.createQuery(hql2);

        List list = query.list();

        System.out.println(list);
        //----------------------------------------------------
        tx.commit();
        session.close();

    }

    @Test
    //条件查询
    public void fun3(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql1 = " from  domain.Customer where cust_id =? ";//？按所有传值
        String hql2 = " from  domain.Customer where cust_id = :id ";//:按名称传值

        Query query = session.createQuery(hql2);

        //query.setParameter(0, 5l);
        query.setParameter("id", 5l);

        List list = query.list();

        System.out.println(list);
        //----------------------------------------------------
        tx.commit();
        session.close();

    }

    @Test
    //分页查询
    public void fun4(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql1 = " from  domain.Customer  ";//完整写法

        Query query = session.createQuery(hql1);

        //类似SQL中的limit ?,?
        // (当前页数-1)*每页条数
        query.setFirstResult(0);
        query.setMaxResults(2);

        List list = query.list();

        System.out.println(list);
        //----------------------------------------------------
        tx.commit();
        session.close();

    }

    @Test
    //统计查询
    //count    计数
    //sum     求和
    //avg    平均数
    //max
    //min
    public void fun5(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql1 = " select count(*) from  domain.Customer  ";
        String hql2 = " select sum(cust_id) from  domain.Customer  ";
        String hql3 = " select avg(cust_id) from  domain.Customer  ";
        String hql4 = " select max(cust_id) from  domain.Customer  ";
        String hql5 = " select min(cust_id) from  domain.Customer  ";

        Query query = session.createQuery(hql3);

        Number number  = (Number) query.uniqueResult();

        System.out.println(number);
        //----------------------------------------------------
        tx.commit();
        session.close();

    }

    @Test
    //投影查询
    //查询对象某一个属性
    public void fun6(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql1 = " select cust_name from  domain.Customer  ";
        String hql2 = " select cust_name,cust_id from  domain.Customer  ";
        String hql3 = " select new Customer(cust_id,cust_name) from  domain.Customer  ";
        //如果实体类有相应构造方法，也可以执行

        Query query = session.createQuery(hql2);

        List list = query.list();

        System.out.println(list);

        //----------------------------------------------------
        tx.commit();
        session.close();

    }
}

多表查询：

再创建一个实体类：

package domain;

//联系人实体
public class LinkMan {
    private Long lkm_id;
    private Character lkm_gender;
    private String lkm_name;
    private String lkm_phone;
    private String lkm_email;
    private String lkm_qq;
    private String lkm_mobile;
    private String lkm_memo;
    private String lkm_position;

    // 表达多对一关系
    private Customer customer;

    public Customer getCustomer() {
        return customer;
    }

    public void setCustomer(Customer customer) {
        this.customer = customer;
    }

    public Long getLkm_id() {
        return lkm_id;
    }

    public void setLkm_id(Long lkm_id) {
        this.lkm_id = lkm_id;
    }

    public Character getLkm_gender() {
        return lkm_gender;
    }

    public void setLkm_gender(Character lkm_gender) {
        this.lkm_gender = lkm_gender;
    }

    public String getLkm_name() {
        return lkm_name;
    }

    public void setLkm_name(String lkm_name) {
        this.lkm_name = lkm_name;
    }

    public String getLkm_phone() {
        return lkm_phone;
    }

    public void setLkm_phone(String lkm_phone) {
        this.lkm_phone = lkm_phone;
    }

    public String getLkm_email() {
        return lkm_email;
    }

    public void setLkm_email(String lkm_email) {
        this.lkm_email = lkm_email;
    }

    public String getLkm_qq() {
        return lkm_qq;
    }

    public void setLkm_qq(String lkm_qq) {
        this.lkm_qq = lkm_qq;
    }

    public String getLkm_mobile() {
        return lkm_mobile;
    }

    public void setLkm_mobile(String lkm_mobile) {
        this.lkm_mobile = lkm_mobile;
    }

    public String getLkm_memo() {
        return lkm_memo;
    }

    public void setLkm_memo(String lkm_memo) {
        this.lkm_memo = lkm_memo;
    }

    public String getLkm_position() {
        return lkm_position;
    }

    public void setLkm_position(String lkm_position) {
        this.lkm_position = lkm_position;
    }

}

测试类：

package hql;

import java.util.Arrays;
import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import domain.Customer;
import utils.HibernateUtils;

//学习HQL语法(不常用) - 多表查询语法
public class Demo2 {
    //原生SQL中：
    // 交叉连接-笛卡尔积(避免)
//        select * from A,B
    // 内连接
//        |-隐式内连接
//            select * from A,B  where b.aid = a.id
//        |-显式内连接
//            select * from A inner join B on b.aid = a.id
    // 外连接
//        |- 左外
//            select * from A left [outer] join B on b.aid = a.id
//        |- 右外
//            select * from A right [outer] join B on b.aid = a.id
//---------------------------------------------------------------------
//HQL的多表查询
        //内连接(迫切)
        //外连接
//            |-左外(迫切)
//            |-右外(迫切)

    @Test
    //HQL 内连接 => 将连接的两端对象分别返回.放到数组中.
    public void fun1(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql = " from Customer c inner join c.linkMens ";
        //c相当于别名
        Query query = session.createQuery(hql);

        List<Object[]> list = query.list();

        for(Object[] arr : list){
            System.out.println(Arrays.toString(arr));
        }
        //----------------------------------------------------
        tx.commit();
        session.close();

    }

    @Test
    //HQL 迫切内连接 => 帮我们进行封装.返回值就是一个对象
    public void fun2(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql = " from Customer c inner join fetch c.linkMens ";

        Query query = session.createQuery(hql);

        List<Customer> list = query.list();

        System.out.println(list);
        //----------------------------------------------------
        tx.commit();
        session.close();

    }

    @Test
    //HQL 左外连接 => 将连接的两端对象分别返回.放到数组中.
    public void fun3(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql = " from Customer c left join c.linkMens ";

        Query query = session.createQuery(hql);

        List<Object[]> list = query.list();

        for(Object[] arr : list){
            System.out.println(Arrays.toString(arr));
        }
        //----------------------------------------------------
        tx.commit();
        session.close();

    }
    @Test
    //HQL 右外连接 => 将连接的两端对象分别返回.放到数组中.
    public void fun4(){
        Session session = HibernateUtils.openSession();
        Transaction tx = session.beginTransaction();
        //----------------------------------------------------
        String hql = " from Customer c right join c.linkMens ";

        Query query = session.createQuery(hql);

        List<Object[]> list = query.list();

        for(Object[] arr : list){
            System.out.println(Arrays.toString(arr));
        }
        //----------------------------------------------------
        tx.commit();
        session.close();

    }

}

补上内连接与外连接区别：

原文地址：https://www.cnblogs.com/xuyiqing/p/8454835.html

时间： 2024-10-29 17:46:23

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