ORM-Hibrenate框架的单表查询

1.导入依赖

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
        </dependency>

        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.4.10.Final</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.10</version>
        </dependency>

2.编写hibernate.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>

    <session-factory>
        <!-- 数据源配置 -->
        <property name="connection.username">root</property>
        <property name="connection.password">root</property>
        <property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/test?useUnicode=true&amp;characterEncoding=UTF-8</property>

        <!-- C3P0 -->
        <property name="hibernate.c3p0.acquire_increment">10</property>
        <property name="hibernate.c3p0.idle_test_period">10000</property>
        <property name="hibernate.c3p0.timeout">5000</property>
        <property name="hibernate.c3p0.max_size">30</property>
        <property name="hibernate.c3p0.min_size">5</property>
        <property name="hibernate.c3p0.max_statements">10</property>

        <!-- 数据库方言 -->
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

        <!-- 打印SQL -->
        <property name="show_sql">true</property>

        <!-- 格式化SQL -->
        <property name="format_sql">true</property>

        <!-- 是否自动生成数据库 -->
        <property name="hibernate.hbm2ddl.auto"></property>

        <!-- 注册实体关系映射文件 -->
        <mapping resource="com/southwind/entity/People.hbm.xml"></mapping>
        <mapping resource="com/southwind/entity/Customer.hbm.xml"></mapping>
        <mapping resource="com/southwind/entity/Orders.hbm.xml"></mapping>
        <mapping resource="com/southwind/entity/Account.hbm.xml"></mapping>
        <mapping resource="com/southwind/entity/Course.hbm.xml"></mapping>

    </session-factory>

</hibernate-configuration>

3.编写Orders类

package com.southwind.entity;

import lombok.Data;

@Data
public class Orders {
    private Integer id;
    private String name;
    //一个订单只对应一个顾客
    private Customer customer;
}

4.编写Orders.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>

    <class name="com.southwind.entity.Orders" table="orders">
        <id name="id" type="java.lang.Integer">
            <column name="id"></column>
            <generator class="identity"></generator>
        </id>
        <property name="name" type="java.lang.String">
            <column name="name"></column>
        </property>
        <many-to-one name="customer" class="com.southwind.entity.Customer" column="cid"></many-to-one>
    </class>

</hibernate-mapping>

注：

1.class中的name属性是映射类的全类名，table对应的是数据库中的表名

2.id中的name是主键对应的属性，type对应的是该属性的类型。 column中的name属性对应的是数据库表中的属性。

3.property中的name值对应的是映射类的属性， column中的name属性是与其对应的是数据库表中的属性。

4.many-to-one是多对一映射，即一个顾客可以有多个订单。

5.编写customer类

package com.southwind.entity;

import lombok.Data;

import java.util.Set;

@Data
public class Customer {
    private Integer id;
    private String name;
    //一个顾客可以有多个订单
    private Set<Orders> orders;
}

6.编写Customer.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>

    <class name="com.southwind.entity.Customer" table="customer">

        <id name="id" type="java.lang.Integer">
            <column name="id"></column>
            <generator class="identity"></generator>
        </id>

        <property name="name" type="java.lang.String">
            <column name="name"></column>
        </property>

        <set name="orders" table="orders" lazy="extra">
            <key column="cid"></key>
            <one-to-many class="com.southwind.entity.Orders"></one-to-many>
        </set>

    </class>

</hibernate-mapping>

注：

1.set属性主要用于一对多的映射关系中，其中从顾客的角度来说，订单可以多个，故在顾客中类中用Set集合作为属性，key属性代表orders表中的外键，one-to-many属性代表一对多的关系，从顾客的角度来说订单可以多个，与many-to-one相对应。

7.测试

package com.southwind.test;

import com.southwind.entity.Customer;
import com.southwind.entity.Orders;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class Test2 {
    public static void main(String[] args) {
        //创建 Configuration
        Configuration configuration = new Configuration().configure("hibernate.xml");
        //获取 SessionFactory
        SessionFactory sessionFactory = configuration.buildSessionFactory();
        //获取 Session
        Session session = sessionFactory.openSession();
        //创建 Customer
        Customer customer = new Customer();
        customer.setName("张三");

        //创建 Orders
        Orders orders = new Orders();
        orders.setName("订单1");

        //建立关联关系
        orders.setCustomer(customer);

        //保存
        session.save(customer);
        session.save(orders);

        //提交事务
        session.beginTransaction().commit();

        //关闭session
        session.close();
    }
}