MyBatis columns mapping

Question

I am using MyBatis 3.0.3 and have problem: some columns in database have names with underscores and these columns should be mapped to the entity properties (that are of course in camelCase)

class User {
  private String first_name;
  ...
}

public interface UserDao {
  @Select("SELECT * FROM users")
  List<User> findAllUsers();
}

Unfortunately I can't see any way to solve that declaretively (like it is done in JPA - @Column(name = "first_name")). I could make aliases in select-clause for such columns (sush as first_name as firstName and etc.), but that also looks lame.

Any ideas? Thanks.

Answer 1

Thanks to DwB. That helped:

    @Select("SELECT * FROM users")
    @Results({
        @Result(property = "firstName", column = "first_name"),
        @Result(property = "lastName", column = "last_name")
    })
    List<User> findUsers();

ps But in case of multiple queries I need to boilerplate @Results/@Result code for each method where entity User is returned. In my case there will be a very few places so it isn't a problem, but in general I would still like to find more general solution.

Answer 2

Eduardo Macarron has suggested this feature on the following issue:

https://code.google.com/p/mybatis/issues/detail?id=43

According to the documentation of MyBatis 3, now is possible through a setting described in:

http://mybatis.github.io/mybatis-3/configuration.html#settings

Basically you must configure:

<setting name="mapUnderscoreToCamelCase" value="true"/>

Which means:

Enables automatic mapping from classic database column names A_COLUMN to camel case classic Java property names aColumn.

Answer 3

Define a ResultMap in the UserMapper.xml file, and add these lines:

<resultMap id="BaseResultMap" type="package.for.User">
  <result column="user_name" jdbcType="VARCHAR" property="userName" />
  <!--  other columns -->
</resultMap>

In your Java code, add@ResultMap annotation:

public interface UserDao {
  @Select("SELECT * FROM users")
  @ResultMap("BaseResultMap")
  List<User> findAllUsers();
}

You can use MyBatis Generator to generate these base codes automatically.

Answer 4

If there is not so much columns you can do it this way and avoid ResultMap.

@Select("SELECT first_name as firstName, last_name as lastName FROM users")
List<User> findUsers();

to make it more readable you can use array of strings, which MyBatis concanate with extra space

@Select({
     "SELECT",
     "  first_name as firstName,",
     "  last_name as lastName",
     "FROM users"})
List<User> findUsers();

Answer 5

In spring annotation-based configuration underscore to camel case mapping can be enabled through a customizable SqlSessionFactory, like that:

@Bean
@Primary
public SqlSessionFactory sqlSessionFactory() throws Exception {
    SqlSessionFactory factory = sessionFactoryBuilder().build();
    factory.getConfiguration().setMapUnderscoreToCamelCase(true);
    // other configurations
    return factory;
}

Answer 6

use MyBatis's Auto-mapping in your config file (sth like application.properties or application.yml), here like:

mybatis.configuration.map-underscore-to-camel-case=true

Reference: http://www.mybatis.org/mybatis-3/sqlmap-xml.html#Auto-mapping

Chinese Reference: http://www.mybatis.org/mybatis-3/zh/sqlmap-xml.html#Auto-mapping