MyBatis | Mapping Query Results to Arbitrary Java Objects | Specifying a Prefix for Column Names

Data tables

foo_table

id	bar_id
1	3
2	2
3	1

bar_table

id
1
2
3

Source code

Foo.java

package sample.mybatis;

public class Foo {
    private int id;
    private Bar bar;

    @Override
    public String toString() {
        return "Foo [id=" + id + ", bar=" + bar + "]";
    }
}

Bar.java

package sample.mybatis;

public class Bar {
    private int id;

    @Override
    public String toString() {
        return "Bar [id=" + id + "]";
    }
}

sample_mapper.xml

<?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="sample.mybatis">

  <resultMap type="sample.mybatis.Foo" id="fooResultMap">
    <id property="id" column="id" />
    <!-- Specify the shared prefix with columnPrefix. -->
    <association property="bar" columnPrefix="bar_" resultMap="barResultMap" />
  </resultMap>

  <resultMap type="sample.mybatis.Bar" id="barResultMap">
    <id property="id" column="id" />
  </resultMap>

  <select id="selectFoo" resultMap="fooResultMap">
    select foo.id
          ,bar.id bar_id -- Specify "bar_" as the prefix.
      from foo_table foo
          ,bar_table bar
     where bar.id = foo.bar_id
  order by foo.id asc
  </select>
</mapper>

Execution result of selectFoo

Foo [id=1, bar=Bar [id=3]]
Foo [id=2, bar=Bar [id=2]]
Foo [id=3, bar=Bar [id=1]]

Explanation

When performing a JOIN, you will usually add a prefix such as bar_ to distinguish columns with the same name in different tables.
MyBatis provides the columnPrefix attribute so that resultMap can also be used in such cases.
When columnPrefix is specified, mapping is performed using names that add the prefix to the column settings.