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Java Mybatis框架多表操作与注解开发详解分析

2024-04-02 19:55

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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();
 
 
}