mybatisplus如何进行多表关联查询？

MyBatis-Plus提供了多种方式来实现多表关联查询，以下是其中两种常用的方法：

方法一：使用@TableName注解和@JoinTable注解

// 创建一个VO类，用于接收多表关联查询的结果
@Data
public class ProductVo {
    private Integer category;
    private Integer count;
    private String description;
    private Integer userId;
    private String userName;
}

// 在对应的Mapper接口中定义多表关联查询的方法
@Select("SELECT p.category, p.count, p.description, u.id AS userId, u.name AS userName " +
        "FROM product p " +
        "LEFT JOIN user u ON p.user_id = u.id " +
        "WHERE p.id = #{productId}")
ProductVo selectProductVoById(@Param("productId") Integer productId);

方法二：使用Wrapper对象进行多表关联查询

// 在对应的Mapper接口中定义多表关联查询的方法
@Select("SELECT p.category, p.count, p.description, u.id AS userId, u.name AS userName " +
        "FROM product p " +
        "LEFT JOIN user u ON p.user_id = u.id " +
        "WHERE p.id = #{productId}")
@Results({
    @Result(column = "category", property = "category"),
    @Result(column = "count", property = "count"),
    @Result(column = "description", property = "description"),
    @Result(column = "userId", property = "userId"),
    @Result(column = "userName", property = "userName")
})
ProductVo selectProductVoById(@Param("productId") Integer productId);

以上两种方法都可以实现多表关联查询，根据具体的业务需求选择适合的方法即可。