MyBatis(3.2.3) - One-to-one mapping using nested Select

We can get Student along with the Address details using a nested Select query as follows:

<resultMap type="Address" id="AddressResult">
    <id property="addrId" column="addr_id"/>
    <result property="street" column="street"/>
    <result property="city" column="city"/>
    <result property="state" column="state"/>
    <result property="zip" column="zip"/>
    <result property="country" column="country"/>
</resultMap>
<select id="findAddressById" parameterType="int" resultMap="AddressResult">
    SELECT * FROM ADDRESSES WHERE ADDR_ID = #{id}
</select>

<resultMap type="Student" id="StudentWithAddressResult">
    <id property="studId" column="stud_id"/>
    <result property="name" column="name"/>
    <result property="email" column="email"/>
    <association property="address" column="addr_id" select="findAddressById"/>
</resultMap>
<select id="findStudentWithAddress" parameterType="int" resultMap="StudentWithAddressResult">
    SELECT * FROM STUDENTS WHERE STUD_ID = #{Id}
</select>

In this approach, the <association> element's select attribute is set to the statement id findAddressById. Here, two separate SQL statements will be executed against the database, the first one called findStudentById to load student details and the second one called findAddressById to load its address details.

The addr_id column value will be passed as input to the selectAddressById statement.

We can invoke the findStudentWithAddress mapped statement as follows:

StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
Student student = mapper.selectStudentWithAddress(studId);
System.out.println(student);
System.out.println(student.getAddress());