数据库两张表在springboot中写xml如何写

1. 创建实体类

首先，我们需要创建对应的Java实体类，以便于操作数据库中的数据。我们假设有两张表：`user`和`order`。

User实体类：

public class User {
    private Long id;
    private String name;
    private Integer age;
    // 省略getter和setter方法
}

Order实体类：

public class Order {
    private Long id;
    private Long userId;
    private String orderNo;
    private Date createTime;
    // 省略getter和setter方法
}

2. 创建Mapper接口

接下来，我们需要创建对应的Mapper接口，用于操作数据库。我们可以使用MyBatis提供的注解方式或者XML方式来编写Mapper接口。这里我们选择使用XML方式来编写Mapper接口。

UserMapper接口：

public interface UserMapper {
    User selectById(Long id);
    List<User> selectAll();
    int insert(User user);
    int update(User user);
    int deleteById(Long id);
}

OrderMapper接口：

public interface OrderMapper {
    Order selectById(Long id);
    List<Order> selectAll();
    List<Order> selectByUserId(Long userId);
    int insert(Order order);
    int update(Order order);
    int deleteById(Long id);
}

3. 创建Mapper XML文件

接下来，我们需要创建对应的Mapper XML文件，这里我们假设分别为`userMapper.xml`和`orderMapper.xml`。

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.example.mapper.UserMapper">
    <resultMap id="userResultMap" type="com.example.entity.User">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
    </resultMap>

    <select id="selectById" resultMap="userResultMap" parameterType="java.lang.Long">
        select * from user where id=#{id}
    </select>

    <select id="selectAll" resultMap="userResultMap">
        select * from user
    </select>

    <insert id="insert" parameterType="com.example.entity.User">
        insert into user(name, age) values (#{name}, #{age})
    </insert>

    <update id="update" parameterType="com.example.entity.User">
        update user set name=#{name}, age=#{age} where id=#{id}
    </update>

    <delete id="deleteById" parameterType="java.lang.Long">
        delete from user where id=#{id}
    </delete>
</mapper>

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.example.mapper.OrderMapper">
    <resultMap id="orderResultMap" type="com.example.entity.Order">
        <id property="id" column="id"/>
        <result property="userId" column="user_id"/>
        <result property="orderNo" column="order_no"/>
        <result property="createTime" column="create_time"/>
    </resultMap>

    <select id="selectById" resultMap="orderResultMap" parameterType="java.lang.Long">
        select * from order where id=#{id}
    </select>

    <select id="selectAll" resultMap="orderResultMap">
        select * from order
    </select>

    <select id="selectByUserId" resultMap="orderResultMap" parameterType="java.lang.Long">
        select * from order where user_id=#{userId}
    </select>

    <insert id="insert" parameterType="com.example.entity.Order">
        insert into order(user_id, order_no, create_time) values (#{userId}, #{orderNo}, #{createTime})
    </insert>

    <update id="update" parameterType="com.example.entity.Order">
        update order set user_id=#{userId}, order_no=#{orderNo}, create_time=#{createTime} where id=#{id}
    </update>

    <delete id="deleteById" parameterType="java.lang.Long">
        delete from order where id=#{id}
    </delete>
</mapper>

4. 配置Mapper

最后，我们需要将Mapper配置到Spring Boot中。这里我们可以使用MyBatis提供的自动配置方式或者手动配置方式来配置Mapper。

自动配置方式：

在`application.properties`中添加如下配置：

mybatis.mapper-locations=classpath:mapper/*.xml

手动配置方式：

@Configuration
@MapperScan("com.example.mapper")
public class MyBatisConfig {
    @Bean
    public SqlSessionFactoryBean sqlSessionFactoryBean() throws Exception {
        SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
        sessionFactory.setDataSource(dataSource());
        sessionFactory.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));
        return sessionFactory;
    }

    @Bean
    public DataSource dataSource() {
        // 配置数据源
    }

    @Bean
    public DataSourceTransactionManager transactionManager() {
        return new DataSourceTransactionManager(dataSource());
    }
}

这里我们使用了注解`@MapperScan`来扫描Mapper接口，并且手动配置了SqlSessionFactoryBean、DataSource和DataSourceTransactionManager。同时，我们需要在`application.properties`中配置数据库连接信息。