Decrypting the MyBatis operation process: in-depth discussion of the key principles of the ORM framework

ORM (Object-Relational Mapping) is a technology for mapping between object models and relational databases. It allows us to operate the database in an object-oriented manner and avoid cumbersome work. Writing SQL statements improves development efficiency. MyBatis is an excellent ORM framework that is widely used in Java development. This article will delve into the execution process of MyBatis, reveal its core mechanism, and combine it with specific code examples to better understand its operating principles.

1. Introduction to MyBatis

MyBatis is an excellent persistence layer framework that simplifies interaction with the database, decouples SQL statements from Java code, and provides flexible mapping relationship configuration. , can meet various complex needs. The core idea of ​​MyBatis is to map SQL statements and Java objects, and realize the mapping relationship between SQL statements and Java objects through configuration files.

2. MyBatis execution process

The execution process of MyBatis can be simply divided into four steps: configuration file parsing, SQL statement parsing, parameter processing and result mapping. Next, the execution process of each step will be explained in detail.

2.1 Configuration file analysis

The configuration file of MyBatis is usually mybatis-config.xml, which contains the configuration of the data source, the configuration of the mapping file, etc. MyBatis will read and parse this configuration file when it starts, and load the configuration information into memory for subsequent use.

<?xml version="1.0" encoding="UTF-8" ?>
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/example/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

2.2 SQL statement parsing

MyBatis will read the mapping file (usually ending with Mapper.xml), parse the SQL statement in it, and based on the configured parameter type Perform type conversion with the result type. The following is a simple example:

<?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" parameterType="int" resultType="User">
        SELECT * FROM user WHERE id = #{id}
    </select>
</mapper>

2.3 Parameter processing

Before executing the SQL statement, MyBatis will process the incoming parameters and compare the parameters with the placeholders in the SQL statement. Match and replace with specific values. Parameter processing is one of the key steps for MyBatis to execute SQL, ensuring the correctness of the SQL statement.

public User getUserById(int id) {
    SqlSession sqlSession = sqlSessionFactory.openSession();
    User user = sqlSession.selectOne("com.example.mapper.UserMapper.getUserById", id);
    sqlSession.close();
    return user;
}

2.4 Result mapping

After executing the SQL statement, MyBatis will convert the result set returned by the database into a Java object and return it to the caller. Specify the type of result mapping through resultType in the configuration file, and MyBatis will automatically perform type conversion.

public class User {
    private int id;
    private String name;
    // 省略getter和setter方法
}

3. Summary

MyBatis is an excellent ORM framework, and its execution process includes configuration file parsing, SQL statement parsing, parameter processing, and result mapping. An in-depth understanding of the execution process and core mechanism of MyBatis will help you better utilize MyBatis for development work. I hope the content of this article can be helpful to readers.

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