1、在其中UserMapper.xm增加一对多的嵌套查询实现。写出测试代码2、在其中UserMapper.xm或OrdersMapper.xml增加多对多关联映射，把对应的产品(productList)找出来写出测试代码

在MyBatis中，实现一对一或多对多的嵌套查询通常涉及XML配置文件（如UserMapper.xml和OrdersMapper.xml）的修改以及编写测试代码。这里假设我们有一个User表和一个Orders表，它们通过用户ID(user_id)关联，每个订单可以有多个产品。

**1. 一对多嵌套查询实现（UserMapper.xml）:**

<mapper namespace="com.example.mapper.UserMapper">
...
<select id="getUserWithOrders" parameterType="int" resultType="com.example.entity.User">
    SELECT u.*
    FROM user u
    LEFT JOIN orders o ON u.user_id = o.user_id
    <choose>
        <when test="o.orderId != null">
            AND o.orderId IN
                <foreach item="item" index="index" collection="ordersIds" open="(" separator="," close=")">
                    #{ordersIds[index]}
                </foreach>
        </when>
        <otherwise>
            <!-- 如果orderId为空，则获取全部订单 -->
            AND o.user_id = u.user_id
        </otherwise>
    </choose>
</select>
...
</mapper>

**测试代码（JUnit示例）:**

import org.junit.Test;
import com.example.entity.User;
import com.example.mapper.UserMapper;
import org.springframework.beans.factory.annotation.Autowired;
public class UserMapperTest {
    @Autowired
    private UserMapper userMapper;

    @Test
    public void testGetUserWithOrders() {
        List<Integer> orderIdList = Arrays.asList(1, 2);
        User user = userMapper.getUserWithOrders(1);
        // 验证查询结果包含正确的订单信息
        assertEquals(orderIdList.size(), user.getOrders().size());
        for (Order order : user.getOrders()) {
            assertTrue(orderIdList.contains(order.getId()));
        }
    }
}

**2. 多对多关联映射（UserMapper.xml 和 OrdersMapper.xml）:**
对于多对多关联，我们需要额外创建一个中间表（例如user_product），并更新映射。假设Product表与User表通过user_product表连接：

<!-- UserMapper.xml -->
<association property="products" javaType="List<Product>" select="getProductsByUser">
    SELECT p FROM product p INNER JOIN user_product up ON p.product_id = up.product_id WHERE up.user_id = #{id}
</association>

<!-- OrdersMapper.xml -->
<select id="getProductsByUser" parameterType="int" resultType="Product">
    SELECT p FROM product p JOIN user_product up ON p.product_id = up.product_id WHERE up.user_id = #{userId} AND up.order_id IN (
        SELECT DISTINCT order_id FROM user_product WHERE user_id = #{userId}
    )
</select>

**测试代码（继续上面的例子）:**

@Test
public void testGetUserWithProducts() {
    int userId = 1;
    User user = userMapper.getUser(userId);
    // 验证查询结果包含用户的所有产品
    for (Order order : user.getOrders()) {
        for (Product product : order.getProducts()) {
            assertNotNull(product);
        }
    }
}