Fetching multiple embedded objects mybatis - mybatis

Question

Class User{
private String employeeId;
private Country assignedCountry;
private Region employeeRegion;
//getter & setter
}
Class Country{
private String countryCode;
private Region countryRegion;
//getter & setter methods
}
Class Region{
private String regionCode;
}
<resultMap type="User" id="userResultMap">
<id column="employee_id" property="employeeId" />
<association property="assignedCountry" resultMap="countryResultMap"/>
<association property="employeeRegion" resultMap="regionResultMap"/>
</resultMap>
<resultMap type="Country" id="countryResultMap">
<id column="country_cd" property="countryCode" />
<association property="countryRegion" resultMap="regionResultMap"/>
</resultMap>
<resultMap type="Region" id="regionResultMap">
<id column="region_cd" property="regionCode" />
<id column="region_nm" property="regionName" />
</resultMap>
Employee is assigned to a country and also belongs to a region.
Country belongs to a region, which may or may not be the same as the employee's region.
The query will fetch the users assigned country and region.
select U.*, C.*, R.* from
User U left outer join Country C
on U.assigned_country_cd = C.country_cd
left outer join Region R
on U.employee_region_cd = R.region_cd
When I execute the query via mybatis and check the user object, I can see that the user region is set properly.
But I can also see that the Region object within the User's country is also set to the user's region. Which shouldn't be the case.
(I understand that I am not fetching the country region here. But if so, this object should not be set at all, rather than setting employee region to the country region)
Can some one please help me on how to map the Country's region within the country object?
I am very new to mybatis and ORM. Any help to shed some light into this would be appreciated.

Answer 1

In your query, you are joining the Region table, not with Country table, but with User table, which ultimately returns the region of the employee (and the countryRegion property of the Country object as well).
In your ResultMap, regionResultMap maps as follows:
region_cd -> regionCode
region_nm -> regionName
You are mapping region_cd column, both to the user.assignedCountry.countryRegion.regionCode and to the user.employeeRegion.regionCode in the same time that basically sets the same columns to same properties in different objects.
What you can do is to differentiate User's region and Country's region in your SQL and map in MyBatis accordingly:
Add another join to connect region with the country:
select U.*, C.*, R.*, CR.region_cd AS C_region_cd, CR.region_nm as C_region_nm from
User U left outer join Country C
on U.assigned_country_cd = C.country_cd
left outer join Region R
on U.employee_region_cd = R.region_cd
left outer join Region CR
on CR.belongsTo = C.country_cd
And, you need to change your ResultMap as follows in order to use the same ResultMap with a different column name. Here, belongsTo is the column in your Region table that shows which Country it belongs to :
<resultMap type="User" id="userResultMap">
<id column="employee_id" property="employeeId" />
<association property="assignedCountry" resultMap="countryResultMap"/>
<association property="employeeRegion" resultMap="regionResultMap"/>
</resultMap>
<resultMap type="Country" id="countryResultMap">
<id column="country_cd" property="countryCode" />
<association columnPrefix="C_" property="countryRegion" resultMap="regionResultMap"/>
</resultMap>
<resultMap type="Region" id="regionResultMap">
<id column="region_cd" property="regionCode" />
<id column="region_nm" property="regionName" />
</resultMap>