MyBatis introduction

 MyBatis is a Java persistence framework that couples objects with stored procedures or SQL statements using an XML descriptor or annotations.

MyBatis is free software that is distributed under the Apache License 2.0.

MyBatis is a fork of iBATIS 3.0 and is maintained by a team that includes the original creators of iBATIS. 

MyBatis is a first class persistence framework with support for custom SQL, stored procedures and advanced mappings. MyBatis eliminates almost all of the JDBC code and manual setting of parameters and retrieval of results. MyBatis can use simple XML or Annotations for configuration and map primitives, Map interfaces and Java POJOs (Plain Old Java Objects) to database records

Feature summary

Unlike ORM frameworks, MyBatis does not map Java objects to database tables but Java methods to SQL statements.

MyBatis lets you use all your database functionality like stored procedures, views, queries of any complexity and vendor proprietary features. It is often a good choice for legacy or de-normalized databases or to obtain full control of SQL execution.

It simplifies coding compared to JDBC. SQL statements are executed with a single line.

MyBatis provides a mapping engine that maps SQL results to object trees in a declarative way.

SQL statements can be built dynamically by using a built-in language with XML-like syntax or with Apache Velocity using the Velocity integration plugin.

MyBatis integrates with Spring Framework and Google Guice. This feature allows one to build business code free of dependencies.

MyBatis supports declarative data caching. A statement can be marked as cacheable so any data retrieved from the database will be stored in a cache and future executions of that statement will retrieve the cached data instead hitting the database. MyBatis provides a default cache implementation based on a Java HashMap and default connectors for integrating with: OSCache, Ehcache, Hazelcast and Memcached. It provides an API to plug other cache implementations. 

Usage

Theare are two ways to use MyBatis: SQL statements are stored in XML files or annotations. Below depicts a MyBatis mapper, that consists of a Java interface with some MyBatis annotations:

package org.mybatis.example;

public interface BlogMapper {
    @Select("select * from Blog where id = #{id}")
    Blog selectBlog(int id);
}

The sentence is executed as follows.

BlogMapper mapper = session.getMapper(BlogMapper.class);
Blog blog = mapper.selectBlog(101);

SQL statements and mappings can also be externalized to an XML file as follows.

<?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="org.mybatis.example.BlogMapper">
    <select id="selectBlog" parameterType="int" resultType="Blog">
        select * from Blog where id = #{id}
    </select>
</mapper>

Statements can also be executed using the MyBatis API.

Blog blog = session.selectOne("org.mybatis.example.BlogMapper.selectBlog", 101);

For details, please refer to the User Guide available at MyBatis site. See external links. 

Spring integration

MyBatis integrates with Spring Framework. This module allows MyBatis to participate in Spring transactions. It will also build MyBatis mappers and sessions and inject them into other beans.

The following sample shows a basic XML configuration that sets up a mapper and injects it into a "BlogService" bean.

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
</bean>

<bean id="blogMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
    <property name="sqlSessionFactory" ref="sqlSessionFactory" />
    <property name="mapperInterface" value="org.mybatis.example.BlogMapper" />
</bean>

<bean id="blogService" class="org.mybatis.example.BlogServiceImpl">
    <property name="blogMapper" ref="blogMapper" />
</bean>

Calling MyBatis is now just calling a bean:

public class BlogServiceImpl implements BlogService {

    private BlogMapper blogMapper;

    public void setBlogMapper(BlogMapper blogMapper) {
        this.blogMapper = blogMapper;
    }

    public void doSomethingWithABlog(int blogId) {
        Blog blog = blogMapper.selectBlog(blogId);
        ...
    }
}

MyBatis Generator

MyBatis provides a code generator. MyBatis Generator will introspect a database table (or many tables) and generate MyBatis artifacts needed to perform CRUD operations (Create, Retrieve, Update, Delete).

An Eclipse plugin is available.

It will preserve any custom code in case of regeneration but only if you use the Eclipse plugin. 

MyBatis is also used in IntelliJ IDEA.

Link guide: http://mybatis.org/generator/

MyBatis-Spring

MyBatis-Spring integrates MyBatis seamlessly with Spring. This library allows MyBatis to participate in Spring transactions, takes care of building MyBatis mappers and SqlSessions and inject them into other beans, translates MyBatis exceptions into Spring DataAccessExceptions, and finally, it lets you build your application code free of dependencies on MyBatis, Spring or MyBatis-Spring.

MyBatis-Spring requires following versions:

MyBatis-Spring	MyBatis	Spring Framework	Spring Batch	Java
2.0	3.5+	5.0+	4.0+	Java 8+
1.3	3.4+	3.2.2+	2.1+	Java 6+

Reference documents

https://en.wikipedia.org/wiki/MyBatis

https://blog.mybatis.org/

https://www.baeldung.com/spring-mybatis

https://www.fatalerrors.org/a/spring-summary-learning-08-integrating-mybatis.html

https://www.youtube.com/watch?v=JyythoOXdbU

https://programmer.ink/think/mybatis-spring-source-analysis.html

https://programmer.help/blogs/implementation-principle-of-mybatis-spring.html

https://programming.vip/keywords/mybatis

https://terasolunaorg.github.io/guideline/5.0.2.RELEASE/en/ArchitectureInDetail/DataAccessMyBatis3.html