Mybatis-plus IPage paging common problems (pit)

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The IDEA version used in this article is ultimate 2019.1, and the JDK version is 1.8.0_141.

1.TooManyResultsException

Recently, when using the IPage plug-in of Mybatis-plus for paging, the following inexplicable error occurred

Resolved [org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.TooManyResultsException: Expected one result (or null) to be returned by selectOne(), but found: 6]

Then I checked the Controller, Service, Mapper, Mapper.xml I wrote, and the result was nothing. The following are my Mapper and Mapper.xml (the content is roughly the same)

Mapper

public interface ExampleMapper {
    
    
    IPage<EntityDto> selectEntityAndPage(@Param("param") Entity param, Page<Entity> page);
}

The select part of Mapper.xml

  <select id="selectEntityAndPage" parameterType="cn.com.example.enetity.Entity " resultType="cn.com.example.dto.EntityDto">
    select id, name from table
  </select>

Baidu discovered this deep pit after a while

The page parameter in mybatis-plus is not in the first position, and the returned result set receiving object is not considered a collection, but it is no problem in the first position.

So I rewritten the order of Mapper parameters

IPage<EntityDto> selectEntityAndPage(Page<Entity> page, @Param("param") Entity param);

problem solved.