Beginning MyBatis 3 Part 2 : How to Handle One-to-Many and One-to-One Selects

One of the latest MyBatis feature is the ability to use Annotations or XML to do One-to-One or One-to-Many queries. Let’s start with an example, as usual im using PostgreSQL, Netbeans 6.9 and MyBatis 3.0.2.
First is a simple database with 2 different tables,

CREATE DATABASE test CREATE TABLE master     (         nama CHARACTER VARYING(30) NOT NULL,         usia SMALLINT,         CONSTRAINT idnama PRIMARY KEY (nama)     ) CREATE TABLE contoh     (         id INTEGER NOT NULL,         nama CHARACTER VARYING(30),         alamat CHARACTER VARYING(50),         CONSTRAINT id PRIMARY KEY (id)     ) ALTER TABLE     contoh ADD CONSTRAINT master FOREIGN KEY (nama) REFERENCES master (nama)     ON DELETE CASCADE     ON UPDATE CASCADE  insert into master (nama, usia) values ('pepe', 17); insert into master (nama, usia) values ('bubu', 19);  insert into contoh (id, nama, alamat) values (1, 'bubu', 'Tangerang'); insert into contoh (id, nama, alamat) values (2, 'pepe', 'Jakarta'); insert into contoh (id, nama, alamat) values (3, 'bubu', 'Singapore'); insert into contoh (id, nama, alamat) values (4, 'pepe', 'Kuburan'); 

My java bean, as my java object representation of my database tables,

package com.edw.bean;  import java.util.List;  public class Master {      private String nama;     private Short usia;     private List<Contoh> contohs;      // other setters and getters      @Override     public String toString() {         return "Master{" + "nama=" + nama + " usia=" + usia + " contohs=" + contohs + '}';     } } 

package com.edw.bean;  public class Contoh {      private Integer id;     private String nama;     private String alamat;     private Master master;      // other setters and getters      @Override     public String toString() {         return "Contoh{" + "id=" + id + " nama=" + nama + " alamat=" + alamat + " master=" + master + '}';     } } 

My XML files for table Contoh and Master queries, please take a look at association tags and collection tags. The association element deals with a has-onetype relationship. While collection deals with a has-lots-of type relationship.

<?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.edw.mapper.MasterMapper" >     <!--    result maps     -->     <resultMap id="ResultMap" type="com.edw.bean.Master" >         <id column="nama" property="nama"  />         <result column="usia" property="usia" />         <!--    collections of Contoh     -->         <collection property="contohs" ofType="com.edw.bean.Contoh"             column="nama" select="selectContohFromMaster" />     </resultMap>      <!--    one to many select  -->     <select id="selectUsingXML" resultMap="ResultMap" parameterType="java.lang.String" >         SELECT             master.nama,             master.usia         FROM             test.master         WHERE master.nama = #{nama}     </select>      <select id="selectContohFromMaster"           parameterType="java.lang.String"           resultType="com.edw.bean.Contoh">         SELECT             id,             nama,             alamat         FROM             test.contoh         WHERE             nama = #{nama}     </select> </mapper> 

<?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.edw.mapper.ContohMapper" >     <!--    result maps     -->     <resultMap id="BaseResultMap" type="com.edw.bean.Contoh" >         <id column="id" property="id" jdbcType="INTEGER" />         <result column="nama" property="nama" jdbcType="VARCHAR" />         <result column="alamat" property="alamat" jdbcType="VARCHAR" />          <!--        one to one     -->         <association property="master" column="nama" javaType="com.edw.bean.Master"             select="selectMasterFromContoh"/>     </resultMap>      <!-- one to one select  -->     <select id="selectUsingXML" resultMap="BaseResultMap" parameterType="java.lang.Integer" >     SELECT         contoh.id,         contoh.nama,         contoh.alamat     FROM         test.contoh     WHERE         id = #{id,jdbcType=INTEGER}     </select>      <select id="selectMasterFromContoh"           parameterType="java.lang.String"           resultType="com.edw.bean.Master">         SELECT             master.nama,             master.usia         FROM             test.master         WHERE             nama = #{nama}     </select> </mapper> 

This is my main xml configuration to handle my database connections,

<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration>     <environments default="development">         <environment id="development">             <transactionManager type="JDBC"/>             <dataSource type="UNPOOLED">                 <property name="driver" value="org.postgresql.Driver"/>                 <property name="url" value="jdbc:postgresql://localhost:5432/test"/>                 <property name="username" value="postgres"/>                 <property name="password" value="password"/>             </dataSource>         </environment>     </environments>     <mappers>         <mapper resource="com/edw/xml/ContohMapper.xml" />         <mapper resource="com/edw/xml/MasterMapper.xml" />     </mappers> </configuration> 

and a java class to load my XML files

package com.edw.config;  import java.io.Reader; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder;  public class MyBatisSqlSessionFactory {      protected static final SqlSessionFactory FACTORY;      static {         try {             Reader reader = Resources.getResourceAsReader("com/edw/xml/Configuration.xml");             FACTORY = new SqlSessionFactoryBuilder().build(reader);         } catch (Exception e){             throw new RuntimeException("Fatal Error.  Cause: " + e, e);         }     }      public static SqlSessionFactory getSqlSessionFactory() {         return FACTORY;     } } 

These are my mapper interfaces, i put my annotation queries here. Please take a note at @Many and @One annotations. MyBatis use @One to map a single property value of a complex type, while @Many for mapping a collection property of a complex types.

package com.edw.mapper;  import com.edw.bean.Contoh; import com.edw.bean.Master; import java.util.List;  import org.apache.ibatis.annotations.Many; import org.apache.ibatis.annotations.Result; import org.apache.ibatis.annotations.Results; import org.apache.ibatis.annotations.Select;  public interface MasterMapper {      Master selectUsingXML(String nama);         /*      *  one to many Select.      */     @Select("SELECT master.nama, master.usia FROM test.master WHERE master.nama = #{nama}")     @Results(value = {                       @Result(property="nama", column="nama"),                       @Result(property="usia", column="usia"),                       @Result(property="contohs", javaType=List.class, column="nama",                              many=@Many(select="getContohs"))                       })     Master selectUsingAnnotations(String nama);      @Select("SELECT contoh.id, contoh.nama, contoh.alamat FROM test.contoh WHERE contoh.nama = #{nama}")     List<Contoh> getContohs(String nama); } 

package com.edw.mapper;  import com.edw.bean.Contoh; import com.edw.bean.Master; import org.apache.ibatis.annotations.One; import org.apache.ibatis.annotations.Result; import org.apache.ibatis.annotations.Results; import org.apache.ibatis.annotations.Select;  public interface ContohMapper {      Contoh selectUsingXML(Integer nama);      /*      *  one to one Select.      */     @Select("SELECT contoh.id, contoh.nama, contoh.alamat FROM test.contoh WHERE contoh.id = #{id}")     @Results(value = {         @Result(property = "nama", column = "nama"),         @Result(property = "alamat", column = "alamat"),         @Result(property = "master", column = "nama", one=@One(select = "getMaster"))     })     Contoh selectUsingAnnotations(Integer id);      @Select("SELECT master.nama, master.usia FROM test.master WHERE master.nama = #{nama}")     Master getMaster(String nama); } 

Here is my main java class

package com.edw.main;  import com.edw.bean.Contoh; import com.edw.bean.Master; import com.edw.config.MyBatisSqlSessionFactory; import com.edw.mapper.ContohMapper; import com.edw.mapper.MasterMapper; import java.util.List; import org.apache.ibatis.session.SqlSession; import org.apache.log4j.Logger;  public class Main {      private static Logger logger = Logger.getLogger(Main.class);      public Main() {     }      private void execute() throws Exception{        SqlSession session = MyBatisSqlSessionFactory.getSqlSessionFactory().openSession();         try {             MasterMapper masterMapper = session.getMapper(MasterMapper.class);              // using XML queries ------------------------------             Master master = masterMapper.selectUsingXML("pepe");             logger.debug(master);              List<Contoh> contohs = master.getContohs();             for (Contoh contoh : contohs) {                 logger.debug(contoh);             }              // using annotation queries ------------------------------             master = masterMapper.selectUsingAnnotations("pepe");             logger.debug(master);              List<Contoh> contohs2 = master.getContohs();             for (Contoh contoh : contohs2) {                 logger.debug(contoh);             }              // using XML queries ------------------------------             ContohMapper contohMapper = session.getMapper(ContohMapper.class);             Contoh contoh = contohMapper.selectUsingXML(1);             logger.debug(contoh.getMaster());              // using annotation queries ------------------------------             contoh = contohMapper.selectUsingAnnotations(1);             logger.debug(contoh);              session.commit();         } finally {             session.close();         }     }      public static void main(String[] args) throws Exception {         try {             Main main = new Main();             main.execute();         } catch (Exception exception) {             logger.error(exception.getMessage(), exception);         }     } } 

And this is what happen on my java console, im using log4j to do all the loggings.

DEBUG java.sql.Connection:27 - ooo Connection Opened DEBUG java.sql.PreparedStatement:27 - ==>  Executing: SELECT master.nama, master.usia FROM test.master WHERE master.nama = ? DEBUG java.sql.PreparedStatement:27 - ==> Parameters: pepe(String) DEBUG java.sql.ResultSet:27 - <==    Columns: nama, usia DEBUG java.sql.ResultSet:27 - <==        Row: pepe, 17 DEBUG java.sql.PreparedStatement:27 - ==>  Executing: SELECT id, nama, alamat FROM test.contoh WHERE nama = ? DEBUG java.sql.PreparedStatement:27 - ==> Parameters: pepe(String) DEBUG java.sql.ResultSet:27 - <==    Columns: id, nama, alamat DEBUG java.sql.ResultSet:27 - <==        Row: 2, pepe, Jakarta DEBUG java.sql.ResultSet:27 - <==        Row: 4, pepe, Kuburan DEBUG com.edw.main.Main:32 - Master{nama=pepe usia=17 contohs=[Contoh{id=2 nama=pepe alamat=Jakarta master=null}, Contoh{id=4 nama=pepe alamat=Kuburan master=null}]} DEBUG com.edw.main.Main:36 - Contoh{id=2 nama=pepe alamat=Jakarta master=null} DEBUG com.edw.main.Main:36 - Contoh{id=4 nama=pepe alamat=Kuburan master=null} DEBUG java.sql.PreparedStatement:27 - ==>  Executing: SELECT master.nama, master.usia FROM test.master WHERE master.nama = ? DEBUG java.sql.PreparedStatement:27 - ==> Parameters: pepe(String) DEBUG java.sql.ResultSet:27 - <==    Columns: nama, usia DEBUG java.sql.ResultSet:27 - <==        Row: pepe, 17 DEBUG java.sql.PreparedStatement:27 - ==>  Executing: SELECT contoh.id, contoh.nama, contoh.alamat FROM test.contoh WHERE contoh.nama = ? DEBUG java.sql.PreparedStatement:27 - ==> Parameters: pepe(String) DEBUG java.sql.ResultSet:27 - <==    Columns: id, nama, alamat DEBUG java.sql.ResultSet:27 - <==        Row: 2, pepe, Jakarta DEBUG java.sql.ResultSet:27 - <==        Row: 4, pepe, Kuburan DEBUG com.edw.main.Main:41 - Master{nama=pepe usia=17 contohs=[Contoh{id=2 nama=pepe alamat=Jakarta master=null}, Contoh{id=4 nama=pepe alamat=Kuburan master=null}]} DEBUG com.edw.main.Main:45 - Contoh{id=2 nama=pepe alamat=Jakarta master=null} DEBUG com.edw.main.Main:45 - Contoh{id=4 nama=pepe alamat=Kuburan master=null} DEBUG java.sql.PreparedStatement:27 - ==>  Executing: SELECT contoh.id, contoh.nama, contoh.alamat FROM test.contoh WHERE id = ? DEBUG java.sql.PreparedStatement:27 - ==> Parameters: 1(Integer) DEBUG java.sql.ResultSet:27 - <==    Columns: id, nama, alamat DEBUG java.sql.ResultSet:27 - <==        Row: 1, bubu, Tangerang DEBUG java.sql.PreparedStatement:27 - ==>  Executing: SELECT master.nama, master.usia FROM test.master WHERE nama = ? DEBUG java.sql.PreparedStatement:27 - ==> Parameters: bubu(String) DEBUG java.sql.ResultSet:27 - <==    Columns: nama, usia DEBUG java.sql.ResultSet:27 - <==        Row: bubu, 19 DEBUG com.edw.main.Main:51 - Master{nama=bubu usia=19 contohs=null} DEBUG java.sql.PreparedStatement:27 - ==>  Executing: SELECT contoh.id, contoh.nama, contoh.alamat FROM test.contoh WHERE contoh.id = ? DEBUG java.sql.PreparedStatement:27 - ==> Parameters: 1(Integer) DEBUG java.sql.ResultSet:27 - <==    Columns: id, nama, alamat DEBUG java.sql.ResultSet:27 - <==        Row: 1, bubu, Tangerang DEBUG java.sql.PreparedStatement:27 - ==>  Executing: SELECT master.nama, master.usia FROM test.master WHERE master.nama = ? DEBUG java.sql.PreparedStatement:27 - ==> Parameters: bubu(String) DEBUG java.sql.ResultSet:27 - <==    Columns: nama, usia DEBUG java.sql.ResultSet:27 - <==        Row: bubu, 19 DEBUG com.edw.main.Main:55 - Contoh{id=1 nama=bubu alamat=Tangerang master=Master{nama=bubu usia=19 contohs=null}} DEBUG java.sql.Connection:27 - xxx Connection Closed 

my log4j.properties

# Global logging configuration log4j.rootLogger=DEBUG,stdout  # Console output... log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.layout=org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern=%-5p %c:%L - %m%n 

And finally, this is my netbeans project structure

Well despite lack of documentations, im still enjoy using MyBatis.