MyBatis Tutorial

Introduction to MyBatis

MyBatis is a popular Java persistence framework that simplifies database interactions by mapping SQL statements to Java methods. Unlike JPA/Hibernate, MyBatis focuses on SQL, allowing developers to write optimized queries while still benefiting from object mapping.

Setting Up MyBatis

1. Add Dependencies

To use MyBatis in a Maven project, add the following dependencies to pom.xml:

<dependencies>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.11</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.33</version>
    </dependency>
</dependencies>

2. Configure MyBatis

Create a mybatis-config.xml file to define settings:

<?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="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/testdb"/>
                <property name="username" value="root"/>
                <property name="password" value="password"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

Creating the Data Model

Define a simple Java class to represent a User entity:

public class User {
    private int id;
    private String name;
    private String email;

    // Getters and Setters
}

Creating a Mapper

Define a mapper XML file UserMapper.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="com.example.mapper.UserMapper">
    <select id="getUserById" resultType="User">
        SELECT * FROM users WHERE id = #{id};
    </select>
    <insert id="insertUser">
        INSERT INTO users (name, email) VALUES (#{name}, #{email});
    </insert>
    <update id="updateUser">
        UPDATE users SET name=#{name}, email=#{email} WHERE id=#{id};
    </update>
    <delete id="deleteUser">
        DELETE FROM users WHERE id=#{id};
    </delete>
</mapper>

Creating the Mapper Interface

Define an interface to match the mapper:

public interface UserMapper {
    User getUserById(int id);
    void insertUser(User user);
    void updateUser(User user);
    void deleteUser(int id);
}

Using MyBatis in Java Code

1. Load MyBatis Configuration

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;

public class MyBatisUtil {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try (InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml")) {
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static SqlSession getSession() {
        return sqlSessionFactory.openSession();
    }
}

2. Perform Database Operations

public class Main {
    public static void main(String[] args) {
        try (SqlSession session = MyBatisUtil.getSession()) {
            UserMapper userMapper = session.getMapper(UserMapper.class);

            // Insert a new user
            User newUser = new User();
            newUser.setName("Alice");
            newUser.setEmail("alice@example.com");
            userMapper.insertUser(newUser);
            session.commit();

            // Retrieve user
            User user = userMapper.getUserById(1);
            System.out.println("User: " + user.getName() + ", " + user.getEmail());
        }
    }
}

Advanced Features

1. Dynamic SQL

MyBatis supports dynamic SQL using <if>, <choose>, and <foreach>:

<select id="searchUsers" resultType="User">
    SELECT * FROM users WHERE 1=1
    <if test="name != null">
        AND name = #{name}
    </if>
    <if test="email != null">
        AND email = #{email}
    </if>
</select>

2. One-to-Many Mapping

Define a relationship where a user has multiple orders:

<resultMap id="UserResultMap" type="User">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="email" column="email"/>
    <collection property="orders" ofType="Order">
        <id property="id" column="order_id"/>
        <result property="amount" column="amount"/>
    </collection>
</resultMap>

<select id="getUserWithOrders" resultMap="UserResultMap">
    SELECT u.*, o.id as order_id, o.amount FROM users u
    LEFT JOIN orders o ON u.id = o.user_id WHERE u.id = #{id};
</select>

Conclusion

MyBatis provides a flexible and powerful way to interact with databases using SQL while still benefiting from object mapping. It is an excellent choice for projects requiring fine-tuned query optimization while maintaining clean, maintainable code.

References

• MyBatis Official Website
• tutorialspoint.com