Having trouble understanding how my Spring DTO works

Question

I'm currently working on a legacy project built by a third-party contractor. It's a Java server which uses Spring and MyBatis and talks to a MySQL server.

I'm trying to refactor some ugly method names in my DTO getters/setters which contain both CamelCase and underscores. I'll use the method getCommon_name() as an example. When I rename it to getCommonName()), the database lookup for that method stops working. I've tried doing a text search to find occurrences in the code where the method is called, but it seems to exist only within the DTO definition. It's possible that there's some automatic mapping to the database that I'm not understanding properly, because that method looks up a table called common_name, but I can't be certain.

Is anyone able to shed some light on what might be happening? This is my first time using Spring/MyBatis.

Edit with more details:

The answers so far have been asking about how my mapping is set up. It looks something like this:

mybatis-config.xml

<configuration>
  <typeAliases>
    <typeAlias type="com.example.dto.SpeciesDTO" alias="species" />
    <!--aliases for other DTOs-->
  </typeAliases>

  <mappers>
    <mapper resource="com/example/dao/species/speciesSQL.xml" />
    <!--aliases for other DAOs-->
  </mappers>
</configuration>

mybatis-context.xml

<beans>
  <bean id="SpeciesDao" class="org.mybatis.spring.mapper.MapperFactoryBean">
    <property name="mapperInterface"
        value="com.example.dao.species.SpeciesDAO" />
    <property name="sqlSessionFactory" ref="sqlSessionFactory" />
  </bean>
  <!--beans for other DAOs-->
</beans>

Also, DAO files all have associated .xml files that look something like this:

<mapper namespace="com.example.species.speciesDAO">
  <select id="getSpecies" parameterType="String" resultType="species">
    SELECT * FROM SPECIES
  </select>
  <!--other methods executing SQL-->
</mapper>

I haven't seen anything that explicitly maps DTO getters/setters the way DAO methods are. For example, if I search for the method getCommon_name(), the only occurrences are the definition in the DTO itself and a call to that method in one of my services (I made sure to edit both occurrences when renaming the method). All the method does is return a property called common_name.

Answer 1

Is there an mybatis-config.xml or other xml mapping file that is setting the convention of names? For example, from here:

<mapper namespace="org.podcastpedia.dao.PodcastDao">
<!--    result maps     -->
<resultMap id="podcastsMap" type="Podcast" >
    <id column="podcast_id" property="podcastId"  />
    <result column="url" property="url" />
    <result column="rating" property="rating" />
    <result column="numberRatings" property="number_ratings" />
    <result column="number_visitors" property="numberOfVisitors" />
    <result column="DESCRIPTION" property="description" />
    <result column="PODCAST_IMAGE_URL" property="urlOfImageToDisplay" />
    <result column="TITLE" property="title" />
    <result column="last_episode_url" property="lastEpisodeMediaUrl" />
    <result column="title_in_url" property="titleInUrl" />
    <result column="publication_date" property="publicationDate"/>
</resultMap>

Answer 2

Like Hibernate, MyBatis is a persistence framework that uses XML files to define which classes and fields map to which database tables.

When you renamed that method in Java, you broke the mapping defined in the XML file. For example, this mapping file defines a SQL select:

<?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="org.mybatis.example.BlogMapper">
  <select id="selectBlog" resultType="Blog">
    select * from Blog where id = #{id}
  </select>
</mapper>

Then the Java implementation to call this:

Blog blog = session.selectOne("org.mybatis.example.BlogMapper.selectBlog", 101);

If, in the Java code, you renamed selectBlog to selectMyBlog and didn't update the map, you'll likely get a NoClassDefFoundError. Make sure that your text search is including all .java files as well as non-Java files such as .xml.

Also, you didn't say which IDE you're using (if any) but I know Hibernate offers plugins for both IDEA and Eclipse. There might be a MyBatis plugin as well that makes this mapping much easier to deal with.