Object‑Oriented Join Queries in MyBatis‑Plus Using the mybatis‑plus‑join Library

In MyBatis, developers often write raw SQL for join queries, but the author prefers an object‑oriented solution.

Because MyBatis‑Plus does not directly support such joins, the mybatis-plus-join library can be used. Add the following Maven dependency to the project:

<dependency>
    <groupId>com.github.yulichang</groupId>
    <artifactId>mybatis-plus-join</artifactId>
    <version>...</version>
</dependency>

After adding the dependency, write Java code that builds a query with MPJQueryWrapper , selects fields, and performs a left join without writing raw SQL:

class Test {
    @Resource
    private UserMapper userMapper;

    void testJoin() {
        MPJQueryWrapper<UserDO> wrapper = new MPJQueryWrapper<UserDO>()
            .selectAll(UserDO.class)
            .select(UserAddrDO::getTel, UserAddrDO::getAddress)
            .leftJoin(UserDO.class, UserDO::getId, UserAddrDO::getUserId)
            .eq(UserAddrDO::getTel, "18888888888");
        // Execute query
        List<UserDTO> list = userMapper.selectJoinList(UserDTO.class, wrapper);
    }
}

This approach keeps the code structure clear, avoids typographical errors common in hand‑written SQL, and showcases the benefits of an object‑oriented query style.