Hibernate学习笔记2

Hibernate映射

一对多  多对一  一对一  多对多

一对多映射

set元素的常用属性

package com.imooc.util;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
    private static SessionFactory sessionFactory;
    private static Session session;
    
    static {
        // 创建Configuration对象  读取hibernate.cfg.cml文件。完成初始化
        Configuration config = new Configuration().configure();
        StandardServiceRegistryBuilder ssrb = new StandardServiceRegistryBuilder().
                applySettings(config.getProperties());
        StandardServiceRegistry ssr = ssrb.build();
        sessionFactory = config.buildSessionFactory(ssr);
    }
        
    // 获取SessionFactory对象
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
    
    // 获取Session
    public static Session getSession() {
        session = sessionFactory.openSession();
        return session;
    }
    
    // 关闭Session
    public static void closeSession(Session session) {
        if (session != null) {
            session.close();
        }
    }
}

单向一对多：

班级（Grade）——>学生（Student）

班级类中有属性 set<Student>

在班级中配置

<!-- 配置单向的一对多关联关系 -->
<set name="students" table="STUDENT">
    <!-- 指定关联的外键 -->
    <key>
        <column name="GID" />
    </key>
    <one-to-many class="com.imooc.entity.Student" />
</set>

package com.imooc.entity;

import java.util.Set;

import org.hibernate.Session;
import org.hibernate.Transaction;

import com.imooc.util.HibernateUtil;

/**
 * 单向的一对多关系
 * @author Administrator
 *
 */
public class Test {
    public static void main(String[] args) {
        //add();
        //findStudentByGrade();
        //update();
        delete();
    }
    // 将学生添加到班级
    public static void add() {
        Grade g = new Grade("一班", "Java软件开发一班");
        Student s1 = new Student("张三", "男");
        Student s2 = new Student("李四", "女");
        
        g.getStudents().add(s1);
        g.getStudents().add(s2);
        
        Session session = HibernateUtil.getSession();
        Transaction tx = session.beginTransaction();
        session.save(g);
        session.save(s1);
        session.save(s2);
        tx.commit();
        HibernateUtil.closeSession(session);
    }
    
    public static void findStudentByGrade() {
        Session session = HibernateUtil.getSession();
        Grade grade = (Grade) session.get(Grade.class, 1);
        Set<Student> students = grade.getStudents();
        for (Student s: students) {
            System.out.println(s);
        }
    }
    // 修改学生信息
    public static void update() {
        Session session = HibernateUtil.getSession();
        Transaction tx = session.beginTransaction();
        Grade g = new Grade("二班", "Java软件开发二班");
        Student student = (Student) session.get(Student.class, 1);
        g.getStudents().add(student);
        session.save(g);
        tx.commit();
        HibernateUtil.closeSession(session);
    }
    // 删除学生信息
    public static void delete() {
        Session session = HibernateUtil.getSession();
        Transaction tx = session.beginTransaction();
        Student student = (Student) session.get(Student.class, 2);
        session.delete(student);
        tx.commit();
        HibernateUtil.closeSession(session);
    }
    
}

单向多对一关联：

1、多对一的关系和关系数据库中的外键参照关系最匹配，即在己方(多方)的表中的一个外键参照另一个表的主键；

2、通过在多方持有一方的引用实现，需要在“多”的一端使用<many-to-one>配置

<!-- 配置多对一关系 -->
<many-to-one name="grade" class="com.imooc.entity.Grade" column="gid" >
</many-to-one>

public static void save() {
    Grade g = new Grade("一班", "Java软件开发一班");
    Student s1 = new Student("张三", "男");
    Student s2 = new Student("李四", "女");
    
    s1.setGrade(g);
    s2.setGrade(g);
    
    Session session = HibernateUtil.getSession();
    Transaction tx = session.beginTransaction();
    session.save(g);
    session.save(s1);
    session.save(s2);
    tx.commit();
    HibernateUtil.closeSession(session);
}

对于inverse属性的说明：

1、一方的hbm.xml文件的<set>节点的inverse属性指定了关联关系的控制方向，默认由one方来维护；

2、关联关系中，inverse="false"则为主动方，由主动方负责维护关联关系；

3、在一对多关联中，设置one方的inverse为true,这将有助于性能的改善。

 cascade属性

《ＨＱＬ数据查询基础》

HQL (Hibernate Query Lanaguage) Hibernate查询语言

HQL是面向对象的查询语言

HQL语句形式：select...from...where...group by...having...order by...

HQL 对Java类的属性大小写敏感，对关键字大小写不敏感

1.from查询一个对象的所有字段（Seller是一个实体类）

String hql = "from Seller";
Query query = session.createQuery(hql);
List<Seller> sellers = query.list();
for (Seller seller: sellers) {
    System.out.println(seller);
}

2.查询指定多个字段，返回的是Object[]

String hql = "select id, name from Seller";
Query query = session.createQuery(hql);
List<Object[]> result = query.list();
for (Object[] objs: result) {
    System.out.println("id:" + objs[0] + ",name:" + objs[1]);
}

3.只查询一个字段，返回的是Object

String hql = "select name from Seller";
Query query = session.createQuery(hql);
List<Object> result = query.list();
for (Object obj: result) {
    System.out.println("name:" + obj);
}

4.查询时可以使用别名，这样查询多个表的时候，可以防止属性名冲突，这里s作为Seller的别名

String hql = "select s.name from Seller s";
Query query = session.createQuery(hql);
List<Object> result = query.list();
for (Object obj: result) {
    System.out.println("name:" + obj);
}

5.list返回查询结果 通过new list()

String hql = "select new list(id,name) from Seller";
Query query = session.createQuery(hql);
List<List> result = query.list();
for (List list: result) {
    System.out.println("id:" + list.get(0) + ",name:" + list.get(1));
}

6.以map形式返回查询结果

String hql = "select new map(id,name) from Seller";
Query query = session.createQuery(hql);
List<Map> maps = query.list();
for (Map map: maps) {
    System.out.println("id:" + map.get("0") + ",name:" + map.get("1"));
}

通过属性的别名获取，注意，如果使用别名就不可以使用下标获取了

String hql = "select new map(id as id_, name as name_) from Seller";
Query query = session.createQuery(hql);
List<Map> maps = query.list();
for (Map map: maps) {
    System.out.println("id:" + map.get("id_") + ",name:" + map.get("name_"));
}

7.以自定义类型返回查询结果

// Seller必须有由id和name组成的构造函数
String hql = "select new Seller(id,name) from Seller";
Query query = session.createQuery(hql);
List<Seller> result = query.list();
for (Seller seller: result) {
    System.out.println("id:" + seller.getId() + ",name:" + seller.getName());
}

public class Seller implements Serializable {
    private Long id;// 主键
    private String name;// 名称
    private String tel;// 电话
        ...  // 其他属性
    
    public Seller(){
        
    }
    public Seller(Long id, String name) {
        this.id = id;
        this.name = name;
    }
    
    ...  // getter & setter
}

8.返回不重复的查询结果 通过distinct关键字

String hql = "select distinct sex from Customer";

条件查询

9.通过比较运算符 =, <, >, <=, >=, <>

 String hql = "from Seller where id > 2"; 

10.判断是否为null

is null 或者 =null 判断为空

is not null 或者 <>null 判断不为空

 String hql = "from Seller where name is not null"; 

11.范围查询

in(a,b,...) 查询值为括号中的某个值的元素 ()中可以是子查询

between a and b 查询值在[a,b]之间的元素

String hql = "from Customer where age in (20, 40)";
String hql = "from Customer where age not in (20, 40)";
String hql = "from Customer where age between 30 and 40";
String hql = "from Customer where age not between 30 and 40";

12.字符串模式匹配

通过like 关键字

通配符：% 匹配任意个字符，_ 匹配一个字符

例：查询名字两个字且姓李的人

String hql = "from Customer where name like '李_' ";

13.逻辑运算 and or

同sql……

14.集合运算

is [not] empty,集合【不】为空，不包含任何元素；对应SQL的exists运算

member of 元素属于集合 ;对应SQL的in运算。

15.四则运算

可以做select子句或者where子句中使用

例： where price*5 > 3000 

16.单个查询

 query.uniqueResult() 如果返回多个查询结果则报错

17.order by子句

对查询结果进行排序

select ... from ... where ... order by ... asc(desc) 默认asc

按多个属性排序，用逗号隔开

总结：和sql好像哦~