java 字段映射排除字段映射关系

转载

mob6454cc7416d1 2024-01-10 22:13:15

文章标签 java 字段映射排除 mybatis xml java 关联映射 文章分类 Java 后端开发

spring中的关联映射

mybatis的映射关系
一对一

加载关联对象的两种方式
代码
IdCard
Person
IdCardMapper.xml
PersonMapper.xml
MyBatisUtils
mybatis-config.xml
Test
Test1
数据库的表

一对多的关联映射

数据库中的表
User
Orders
UserMapper.xml
mybatis-config.xml
Test2

多对多

数据库
Orders
Product
OrdersMapper.xml
ProductMapper.xml
Test3
mybatis-config.xml

mybatis的映射关系

在开发中对数据库操作经常用到多张表，这在面向对象中涉及到对象与对象之间的关联关系，而mybatis提供了关联映射，通过关联映射就可以很好的处理对象与对象之间的关联关系，
在关系型数据库中，多表之间存在着三种关联关系，分别为一对一，一对多，多对多，
在java中，通过对象也可以进行关联关系描述，如下图所示，

一对一

在mybatis中怎末解决一对一的问题呢，在resultMpa元素中包含一个assocation的子元素，通过它可以处理一对一的关联关系

associatin元素中属性
property:指定映射到实体类对象属性，与表字段一一对应。
column:指定表中对应的字段
javaType:指定映射到实体对象属性的类型
select:指定引入嵌套查询的子SQL语句，该属性用于关联映射中的嵌套查询
fetchType：指定在关联查询时是否启用延迟加载，该属性由lazy和eager两个属性值，默认值时lazy(即默认关联映射延迟加载)

加载关联对象的两种方式

嵌套查询和嵌套结果

代码

IdCard

package com.yzb.chapter09;

public class IdCard {
    private Integer id;
    private String code;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    @Override
    public String toString() {
        return "IdCard{" +
                "id=" + id +
                ", code='" + code + '\'' +
                '}';
    }
}

Person

package com.yzb.chapter09;

public class Person {
    private Integer id;
    private String name;
    private Integer age;
    private String sex;
    private IdCard card;//个人关联的证件

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
         = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public IdCard getCard() {
        return card;
    }

    public void setCard(IdCard card) {
        this.card = card;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                ", card=" + card +
                '}';
    }
}

IdCardMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- namespace表示命名空间 -->
<mapper namespace="com.yzb.chapter09.IdCardMapper">
    <!--根据id查询证件信息-->
    <select id="findCodeById" parameterType="Integer" resultType="com.yzb.chapter09.IdCard">
        select * from tb_idcard where id = #{id}
    </select>
</mapper>

PersonMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- namespace表示命名空间 -->
<mapper namespace="com.yzb.chapter09.PersonMapper">
    <!--嵌套查询：通过执行另外一条SQL映射语句来返回预期的特殊类型-->
   <select id="findPersonById" parameterType="Integer" resultMap="IdCardWithPersonResult">
       select * from tb_person where id= #{id}
   </select>
    <resultMap id="IdCardWithPersonResult" type="com.yzb.chapter09.Person">
        <id property="id" column="id"></id>
        <result property="name" column="name"></result>
        <result property="age" column="age"></result>
        <result property="sex" column="sex"></result>
        <!--使用一对一：assocation使用select属性引入另一条SQL语句-->
        <!--property指定的是Person类中定义的IdCard类型的属性名，column是定义在与person对应的数据库表中的IdCard的引入的主键 javaType对应的是映射的IdCard类的-->
        <association property="card" column="card_id" javaType="com.yzb.chapter09.IdCard" select="com.yzb.chapter09.IdCardMapper.findCodeById">
        </association>
    </resultMap>


    <!--嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集-->
    <select id="findPersonById2" parameterType="Integer" resultMap="IdCardWithPersonResult2">
        select p.*,idcard.code from tb_person p ,tb_idcard idcard where p.card_id =  and  = #{id}
    </select>
    <resultMap id="IdCardWithPersonResult2" type="com.yzb.chapter09.Person">
        <id property="id" column="id"></id>
        <result property="name" column="name"></result>
        <result property="age" column="age"></result>
        <result property="sex" column="sex"></result>
        <association property="card" javaType="com.yzb.chapter09.IdCard">
            <id property="id" column="card_id"/>
            <result property="code" column="code"/>
        </association>
    </resultMap>

</mapper>

MyBatisUtils

package com.yzb.chapter09;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

/*
* 工具类
* */
public class MyBatisUtils {
    /*
    * 初始化sqlSessionFactory对象
    * */
    private static SqlSessionFactory sqlSessionFactory = null;
    static {
        try {
            //使用mybatis提供resources类加载MyBatis的配置文件
            InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
            //创建SqlSessionFactory工厂
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //获取SqlSession对象的方法
    public static SqlSession getSession(){
        return sqlSessionFactory.openSession();
    }
}

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <!--打开延迟加载的开关-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <!--将积极加载改为延迟加载，即按需加载-->
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>
    <!--1.配置环境 ，默认的环境id为mysql-->
    <environments default="mysql">
        <!--1.2.配置id为mysql的数据库环境 -->
        <environment id="mysql">
            <!-- 使用JDBC的事务管理 -->
            <transactionManager type="JDBC" />
            <!--数据库连接池 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url"
                          value="jdbc:mysql://localhost:3306/spring" />
                <property name="username" value="root" />
                <property name="password" value="root" />
            </dataSource>
        </environment>
    </environments>
    <!--2.配置Mapper的位置 -->
    <mappers>
        <mapper resource="com/yzb/chapter09/IdCardMapper.xml" />
        <mapper resource="com/yzb/chapter09/PersonMapper.xml"/>
    </mappers>
</configuration>

Test

package com.yzb.chapter09;

import org.apache.ibatis.session.SqlSession;

/*
* MyBatis关联查询映射测试类
* */
public class Test {
    /*
    * 嵌套查询
    * */
    public static void main(String[] args) {
        //通过工具类生成sqlSession对象
        SqlSession session = MyBatisUtils.getSession();
        //执行查询
        Person p =  session.selectOne("com.yzb.chapter09.PersonMapper.findPersonById",1);
        System.out.println(p);
        /*当开启延迟加载的时候，这时只需要加载Person的数据库的SQL语句查询就可以了*/
        System.out.println(p.getName());
        //关闭SqlSession对象
        session.close();
    }
}

Test1

package com.yzb.chapter09;

import org.apache.ibatis.session.SqlSession;

/*
* MyBatis关联查询映射测试类
* */
public class Test1 {
    /*
    * 嵌套结果
    * */
    public static void main(String[] args) {
        //通过工具类生成sqlSession对象
        SqlSession session = MyBatisUtils.getSession();
        //执行查询
        Person p =  session.selectOne("com.yzb.chapter09.PersonMapper.findPersonById2",1);
        System.out.println(p);
        //关闭SqlSession对象
        session.close();
    }
}

数据库的表

tb_person

java 字段映射排除字段映射关系_java

tb_IcCard

java 字段映射排除字段映射关系_java_02

一对多的关联映射

在resultMap元素中使用collection的子元素，使用collection元素完成一对多的关联映射，子元素与association元素相同，但ofType与javaType属性相对应。它用于指定实体对象中集合类型属性包含的元素类型。

java 字段映射排除字段映射关系_关联映射_03

数据库中的表

tb_User

java 字段映射排除字段映射关系_xml_04

tb_orders

java 字段映射排除字段映射关系_java 字段映射排除_05

User

package com.yzb.chapter09.example;

import java.util.List;

public class User {
    private Integer id;
    private String username;
    private String address;
    private List<Orders> ordersList;//用户关联的订单

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", address='" + address + '\'' +
                ", ordersList=" + ordersList +
                '}';
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public List<Orders> getOrdersList() {
        return ordersList;
    }

    public void setOrdersList(List<Orders> ordersList) {
        this.ordersList = ordersList;
    }
}

Orders

package com.yzb.chapter09.example;

public class Orders {
    private Integer id;
    private String number;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    @Override
    public String toString() {
        return "Orders{" +
                "id=" + id +
                ", number='" + number + '\'' +
                '}';
    }
}

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- namespace表示命名空间 -->
<mapper namespace="com.yzb.chapter09.example.UserMapper">
    <!--一对多，查看某一用户及其关联的订单信息-->
    <!--当关联出来的列名相同时，需要使用别名来区分-->
    <select id="findUserWithOrders"  resultMap="UserWithOrdersResult" parameterType="Integer">
        select u.* ,  as order_id ,o.number from tb_user u,tb_orders o where u.id=o.user_id and u.id =#{id}
    </select>
    <resultMap id="UserWithOrdersResult" type="com.yzb.chapter09.example.User">
        <id property="id" column="id"/>
        <result property="username" column="username"/>
        <result property="address" column="address"/>
        <!--一对多关联映射，collection
        ofType表示属性集合元素的类型，List<Orders>属性即Orders类-->
        <collection property="ordersList" ofType="com.yzb.chapter09.example.Orders">
            <id property="id" column="order_id"></id>
            <result property="number" column="number"></result>
        </collection>
    </resultMap>
</mapper>

mybatis-config.xml

<!--2.配置Mapper的位置 -->
    <mappers>
        <mapper resource="com/yzb/chapter09/IdCardMapper.xml" />
        <mapper resource="com/yzb/chapter09/PersonMapper.xml"/>
        <mapper resource="com/yzb/chapter09/example/UserMapper.xml"/>
    </mappers>

Test2

package com.yzb.chapter09.example;

import com.yzb.chapter09.MyBatisUtils;
import com.yzb.chapter09.Person;
import org.apache.ibatis.session.SqlSession;

/*
* MyBatis关联查询映射测试类
* */
public class Test2 {
    /*
    * 嵌套查询
    * */
    public static void main(String[] args) {
        //通过工具类生成sqlSession对象
        SqlSession session = MyBatisUtils.getSession();
        //执行查询
       User user=  session.selectOne("com.yzb.chapter09.example.UserMapper.findUserWithOrders",1);
        System.out.println(user);
        //关闭SqlSession对象
        session.close();
    }
}

多对多

数据库

CREATE TABLE tb_product (
id INT(32) PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR (32),
price DOUBLE
);
INSERT INTO tb_product VALUES('1','Java基础入门','11.0');
INSERT INTO tb_product VALUES('2','Spring','45.0');
INSERT INTO tb_product VALUES('3','JavaWeb','78.0');
CREATE TABLE tb_ordersitem (
id INT(32) PRIMARY KEY AUTO_INCREMENT,
orders_id INT(32),
product_id INT (32),
FOREIGN KEY(orders_id) REFERENCES tb_orders(id),
FOREIGN KEY(product_id) REFERENCES tb_product(id),
)
INSERT INTO tb_ordersitem VALUES('1','1','1');
INSERT INTO tb_ordersitem VALUES('2','1','3');
INSERT INTO tb_ordersitem VALUES('2','3','3');

Orders

package com.yzb.chapter09.example;

import java.util.List;

public class Orders {
    private Integer id;
    private String number;
    private List<Product> productList;

    public List<Product> getProductList() {
        return productList;
    }

    public void setProductList(List<Product> productList) {
        this.productList = productList;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    @Override
    public String toString() {
        return "Orders{" +
                "id=" + id +
                ", number='" + number + '\'' +
                ", productList=" + productList +
                '}';
    }
}

Product

package com.yzb.chapter09.example;

import java.util.List;

/*
* 商品持久层
* */
public class Product {
    private Integer id;
    private String name;
    private Double price;
    private List<Orders> orders;

    @Override
    public String toString() {
        return "Product{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", price=" + price +
                ", orders=" + orders +
                '}';
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
         = name;
    }

    public Double getPrice() {
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    public List<Orders> getOrders() {
        return orders;
    }

    public void setOrders(List<Orders> orders) {
        this.orders = orders;
    }
}

OrdersMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- namespace表示命名空间 -->
<mapper namespace="com.yzb.chapter09.example.OrdersMapper">
    <!--多对多镶嵌查询：通过执行另一条SQL映射语句来返回预期的特殊类型-->
    <select id="findOrdersWithProduct" parameterType="Integer" resultMap="OrdersWithProductResult">
        select * from tb_orders where id= #{id}
    </select>
    <resultMap id="OrdersWithProductResult" type="com.yzb.chapter09.example.Orders">
        <id property="id" column="id"></id>
        <result column="number" property="number"></result>
        <collection property="productList" column="id" ofType="com.yzb.chapter09.example.Product" select="com.yzb.chapter09.example.UserMapper.findProductById">

        </collection>
    </resultMap>
    <!--多对多镶嵌结果：通过执行另一条SQL映射语句来返回预期的特殊类型-->
    <select id="findOrdersWithProduct1" parameterType="Integer" resultMap="OrdersWithProductResult1">
        select o.*, as pid,,p.price,form tb_orders o,tb_product p ,tb_ordersitem oi where oi.orders_id =  and oi.product_id= and  =#{id}
    </select>
    <!--自定义手动映射类型-->
    <resultMap id="OrdersWithProductResult1" type="com.yzb.chapter09.example.Orders">
        <id property="id" column="id"></id>
        <result column="number" property="number"></result>
        <!--多对多关联映射：collection-->
        <collection property="productList"  ofType="com.yzb.chapter09.example.Product" >
            <id property="id" column="pid"/>
            <result property="name" column="name"/>
            <result property="price" column="price"/>
        </collection>
    </resultMap>
</mapper>

ProductMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- namespace表示命名空间 -->
<mapper namespace="com.yzb.chapter09.example.UserMapper">
    <!--多对多镶嵌查询-->
    <select id="findProductById" parameterType="Integer" resultType="com.yzb.chapter09.example.Product">
        select * from tb_product where id in (select product_id from tb_ordersitem where orders_id =#{id})
    </select>
</mapper>

Test3

package com.yzb.chapter09.example;

import com.yzb.chapter09.MyBatisUtils;
import org.apache.ibatis.session.SqlSession;

/*
* MyBatis关联查询映射测试类
* */
public class Test3 {
    /*
    * 嵌套查询
    * */
    public static void main(String[] args) {
        //通过工具类生成sqlSession对象
        SqlSession session = MyBatisUtils.getSession();
        //执行查询
       Orders orders =  session.selectOne("com.yzb.chapter09.example.OrdersMapper.findOrdersWithProduct",1);
        System.out.println(orders);
        //关闭SqlSession对象
        session.close();
    }
}

mybatis-config.xml

<mappers>
        <mapper resource="com/yzb/chapter09/IdCardMapper.xml" />
        <mapper resource="com/yzb/chapter09/PersonMapper.xml"/>
        <mapper resource="com/yzb/chapter09/example/UserMapper.xml"/>
        <mapper resource="com/yzb/chapter09/example/ProductMapper.xml"/>
        <mapper resource="com/yzb/chapter09/example/OrdersMapper.xml"/>
    </mappers>

本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。

上一篇：mysql删字姓名为李康的学生记录 sql删除所有姓李的数据

下一篇：时序量子神经网络神经网络量子态

提问和评论都可以，用心的回复会被更多人看到评论

发布评论

相关文章

官方博客	全部文章	热门标签	班级博客
了解我们	网站地图	意见反馈

鸿蒙开发者社区	51CTO学堂
51CTO	软考资讯

java 字段映射排除 字段映射关系

java 字段映射排除 字段映射关系

spring中的关联映射

mybatis的映射关系

一对一

加载关联对象的两种方式

代码

IdCard

Person

IdCardMapper.xml

PersonMapper.xml

MyBatisUtils

mybatis-config.xml

Test

Test1

数据库的表

一对多的关联映射

数据库中的表

User

Orders

UserMapper.xml

mybatis-config.xml

Test2

多对多

数据库

Orders

Product

OrdersMapper.xml

ProductMapper.xml

Test3

mybatis-config.xml

51CTO博客

java 字段映射排除字段映射关系

java 字段映射排除字段映射关系