Preface

I was a little addicted to mapping Value Objects in MyBatis, so I organized them.

What you want to achieve

I want to map the result of SELECT to a Value Object in the object
I want to set the SELECT parameter to Value Object

environment

Spirng Boot
MyBatis
h2 DataBase

Implementation

Suppose you have a Value Object class called ʻUserName` like this:

package com.example.demo.domain.model;

public class UserName {
    private final String value;

    public UserName(String value) {
        this.value = value;
    }

    public String getValue() {
        return this.value;
    }
}

The ʻUser class holds the ʻUserName. It also holds the classes ʻUserName and RegisterDate`.

package com.example.demo.domain.model;

import lombok.Data;

@Data
public class User {
    private UserId userId;
    private UserName userName;
    private RegisterDate registerDate;
}

Write the DB definition in schema.sql.

CREATE TABLE users (
  id int NOT NULL
  , user_name VARCHAR(50)  
  , register_date DATE
);

Data.sql for inserting data for testing.

INSERT INTO users VALUES (1, 'Nocchi', '2020-02-01');
INSERT INTO users VALUES (2, 'Kashiyuka', '2020-02-02');
INSERT INTO users VALUES (3, 'A-Chan', '2020-02-03');

Define a method findById in ʻUserRepository to get ʻUser from the ID.

package com.example.demo.domain.repository;

import com.example.demo.domain.model.User;
import com.example.demo.domain.model.UserId;

import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.springframework.stereotype.Repository;

@Mapper
@Repository
public interface UserRepository {
    User findById(@Param("userId") UserId userId);
}

Mapper has the following contents.

<?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="com.example.demo.domain.repository.UserRepository">
  <select id="findById" resultMap="UserMap" parameterType="map">
    select id, user_name, register_date from users where id = #{userId.value}
  </select>

  <resultMap id="UserMap" type="com.example.demo.domain.model.User">
      <association property="userId" javaType="com.example.demo.domain.model.UserId">
        <constructor>
          <arg name="value" column="id"/>
        </constructor>
      </association>
      <association property="userName" javaType="com.example.demo.domain.model.UserName">
        <constructor>
          <arg name="value" column="user_name"/>
        </constructor>
      </association>
      <association property="registerDate" javaType="com.example.demo.domain.model.RegisterDate">
        <constructor>
          <arg name="value" column="register_date"/>
        </constructor>
      </association>
  </resultMap>

</mapper>

point

If you want to use Value Object for Parameter of select, add @Param annotation
When using @Param, addparameterType = "map"to the option of select

Without the above, the value of the Value Object could not be used in the select, such aswhere id = # {userId.value}.

Use ʻassociation` to create a Value Object instance in the SELECT result object
Use constructor to map a value to the Value Object's constructor
Specify the argument name with the option name of ʻarg`

The following part.

<association property="userId" javaType="com.example.demo.domain.model.UserId">
        <constructor>
          <arg name="value" column="id"/>
        </constructor>
</association>

result

The result of writing the test code and breaking it is as follows. An instance of the Value Object has also been created and the values have been mapped.

code

Published on GitHub.

Points when mapping Value Object in MyBatis