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Java Mybatis框架多表操作与注解开发详解分析

2024-04-02 19:04:59 364人浏览安东尼

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摘要

目录一对一查询多对多查询mybatis的注解开发Mybatis的增删查改MyBatis的注解实现复杂映射开发一对一查询一对一查询的模型用户表和订单表的关系为，一个用户有多个订单，

一对一查询

一对一查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户。

一对一查询的需求:查询一个订单，与此同时查询出该订单所属的用户

一对一查询的语句

对应的sql语句: select * from orders o,user u where o.uid=u.id;查询的结果如下:

创建Order和User实体

创建OrderMapper接口


public interface OrderMapper {
 
    //查询全部的方法
    public List<Order> findAll();
}

配置OrderMapper.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">
<mapper namespace="com.longdi.mapper.OrderMapper">
 
    <resultMap id="orderMap" type="order">
        <!--手动指定字段与实体属性的映射关系
            column: 数据表的字段名称
            property：实体的属性名称
        -->
        <id column="oid" property="id"></id>
        <result column="ordertime" property="ordertime"></result>
        <result column="total" property="total"></result>
        <!--<result column="uid" property="user.id"></result>
        <result column="username" property="user.username"></result>
        <result column="passWord" property="user.password"></result>
        <result column="birthday" property="user.birthday"></result>-->
 
        <!--
            property: 当前实体(order)中的属性名称(private User user)
            javaType: 当前实体(order)中的属性的类型(User)
        -->
        <association property="user" javaType="user">
            <id column="uid" property="id"></id>
            <result column="username" property="username"></result>
            <result column="password" property="password"></result>
            <result column="birthday" property="birthday"></result>
        </association>
 
    </resultMap>
 
    <select id="findAll" resultMap="orderMap">
         SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id
    </select>
 
</mapper>

配置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">
<mapper namespace="com.longdi.mapper.UserMapper">
 
 
    <resultMap id="userMap" type="user">
        <id column="uid" property="id"></id>
        <result column="username" property="username"></result>
        <result column="password" property="password"></result>
        <result column="birthday" property="birthday"></result>
        <!--配置集合信息
            property:集合名称
            ofType：当前集合中的数据类型
        -->
        <collection property="orderList" ofType="order">
            <!--封装order的数据-->
            <id column="oid" property="id"></id>
            <result column="ordertime" property="ordertime"></result>
            <result column="total" property="total"></result>
        </collection>
    </resultMap>
 
    <select id="findAll" resultMap="userMap">
        SELECT *,o.id oid FROM USER u,orders o WHERE u.id=o.uid
    </select>
 
    <!--#############################################################################-->
 
    <resultMap id="userRoleMap" type="user">
        <!--user的信息-->
        <id column="userId" property="id"></id>
        <result column="username" property="username"></result>
        <result column="password" property="password"></result>
        <result column="birthday" property="birthday"></result>
        <!--user内部的roleList信息-->
        <collection property="roleList" ofType="role">
            <id column="roleId" property="id"></id>
            <result column="roleName" property="roleName"></result>
            <result column="roleDesc" property="roleDesc"></result>
        </collection>
    </resultMap>
 
    <select id="findUserAndRoleAll" resultMap="userRoleMap">
        SELECT * FROM USER u,sys_user_role ur,sys_role r WHERE u.id=ur.userId AND ur.roleId=r.id
    </select>
 
</mapper>

配置sqlMapConfig.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>
 
    <!--通过properties标签加载外部properties文件-->
    <properties resource="jdbc.properties"></properties>
 
    <!--自定义别名-->
    <typeAliases>
        <typeAlias type="com.longdi.domain.User" alias="user"></typeAlias>
        <typeAlias type="com.longdi.domain.Order" alias="order"></typeAlias>
        <typeAlias type="com.longdi.domain.Role" alias="role"></typeAlias>
    </typeAliases>
 
    <!--数据源环境-->
    <environments default="developement">
        <environment id="developement">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    
 
    <!--加载映射文件-->
    <mappers>
        <mapper resource="com/longdi/mapper/UserMapper.xml"></mapper>
        <mapper resource="com/longdi/mapper/OrderMapper.xml"></mapper>
    </mappers>
</configuration>

测试代码


    @Test
    public void test1() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
 
        OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
        List<Order> orderList = mapper.findAll();
        for (Order order : orderList) {
            System.out.println(order);
        }
        sqlSession.close();
    }

一对多查询

一对多查询模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户一对多查询的需求:查询一个用户，与此同时查询出该用户具有的订单

对应的sql语句: select *,o.id oid from user u left join orders o on u.id=o.uid;查询的结果如下:

SELECT *,o.id oid FROM USER u, orders o WHERE u.id=o.uid

修改User实体

创建UserMapper接口

配置UserMapper.xml
测试结果

多对多查询

多对多查询的模型
用户表和角色表的关系为，一个用户有多个角色，一个角色被多个用户使用多对多查询的需求:查询用户同时查询出该用户的所有角色

多对多查询的语句

对应的sql语句: select u.*,r.*,r.id rid from user u left join user_role ur on u.id=ur.user_idinner join role r on ur.role_id=r.id;
查询的结果如下:

创建Role实体，修改User实体

添加UserMapper接口方法

配置UserMapper.xml（上面）
测试代码

总结：

MyBatis多表配置方式:

一对一配置:使用<resultMap>做配置
一对多配置:使用<resultMap>+<collection>做配置

多对多配置:使用<resultMap>+<collection>做配置

Mybatis的注解开发

Mybatis的常用注解

这几年来注解开发越来越流行，Mybatis也可以使用注解开发方式，这样我们就可以减少编写Mapper映射文件了。我们先围绕一些基本的CRUD来学习，再学习复杂映射多表操作。
@Insert:实现新增
@Update:实现更新@Delete:实现删除@Select:实现查询
@Result:实现结果集封装
@Results:可以与@Result一起使用，封装多个结果集@One:实现一对一结果集封装
@Many:实现一对多结果集封装

Mybatis的增删查改


    private UserMapper mapper;
 
    @Before
    public void before() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        mapper = sqlSession.getMapper(UserMapper.class);
    }


   @Test
    public void testSave(){
        User user = new User();
        user.setUsername("tom");
        user.setPassword("abc");
        mapper.save(user);
    }
 
    @Test
    public void testUpdate(){
        User user = new User();
        user.setId(18);
        user.setUsername("lucy");
        user.setPassword("123");
        mapper.update(user);
    }
 
    @Test
    public void testDelete(){
        mapper.delete(18);
    }
 
    @Test
    public void testFindById(){
        User user = mapper.findById(2);
        System.out.println(user);
    }
 
    @Test
    public void testFindAll(){
        List<User> all = mapper.findAll();
        for (User user : all) {
            System.out.println(user);
        }
    }

修改MyBatis的核心配置文件，我们使用了注解替代的映射文件，所以我们只需要加载使用了注解的Mapper接口即可


    <!--加载映射关系-->
    <mappers>
        <!--扫描使用注解的类-->
        <package name="com.longdi.mapper.UserMapper"></package>
    </mappers>

或者指定扫描包含映射关系的接口所在的包也可以


    <!--加载映射关系-->
    <mappers>
        <!--指定接口所在的包-->
        <package name="com.longdi.mapper"></package>
    </mappers>

UserMapper:


public interface UserMapper {
 
    @Insert("insert into user values(#{id},#{username},#{password},#{birthday})")
    public void save(User user);
 
    @Update("update user set username=#{username},password=#{password} where id=#{id}")
    public void update(User user);
 
    @Delete("delete from user where id=#{id}")
    public void delete(int id);
 
    @Select("select * from user where id=#{id}")
    public User findById(int id);
 
    @Select("select * from user")
    public List<User> findAll();
 
    @Select("select * from user")
    @Results({
            @Result(id=true ,column = "id",property = "id"),
            @Result(column = "username",property = "username"),
            @Result(column = "password",property = "password"),
            @Result(
                    property = "orderList",
                    column = "id",
                    javaType = List.class,
                    many = @Many(select = "com.longdi.mapper.OrderMapper.findByUid")
            )
    })
    public List<User> findUserAndOrderAll();
 
 
    @Select("SELECT * FROM USER")
    @Results({
            @Result(id = true,column = "id",property = "id"),
            @Result(column = "username",property = "username"),
            @Result(column = "password",property = "password"),
            @Result(
                    property = "roleList",
                    column = "id",
                    javaType = List.class,
                    many = @Many(select = "com.longdi.mapper.RoleMapper.findByUid")
            )
    })
    public List<User> findUserAndRoleAll();
 
 
}