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  • MyBatis series summary: MyBatis series

preface

  • MyBatis is an excellent persistence layer framework

  • MyBatis eliminates almost all of the JDBC code and manual setting of parameters and retrieving result sets.

  • Official documentation: Documentation

  • Making: making

  • Persistence:

    • That is, data is permanently saved to a storage device, such as a disk.
    • JDBC is also a persistence mechanism. The same goes for file IO.

  • Why is persistence needed?

    • Because memory breakpoints are lost, some data must not be lost, such as bank accounts. But there is no guarantee that the power will never go out.
    • Memory is expensive and maintenance costs are high because it needs to be powered consistently.
    • So we usually persist data in external storage.

First, start the pre-preparation of MyBatis

1.1. Establishment of experimental database
  • Simple experiment, just a few simple fields.

1.2. Import MyBatis related JAR packages
		<dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
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1.3. Write the core configuration file of MyBatis

      
<! DOCTYPEconfiguration
        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.jdbc.Driver"/>
                <property name="url" value="JDBC: mysql: / / IP address: 3306 / mybatis? useSSL=true"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/dbright/mapper/xml/userMapper.xml"/>
    </mappers>
</configuration>
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  • There’s nothing to explain. They’re all fixed templates, similar to SpringBoot’s configuration, but not as simple as SpringBoot’s
  • The only thing to watch out for might be,mappersIn theresourceThis must be consistent with the XML path of the project to map to!

The first MyBatis program

  • With the above preconditions complete, you are ready to start development
2.1. Create an entity class
import lombok.Data;
@Data
public class User {
    private Integer id;
    private String name;
    private Integer age;
    private String like;
}
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2.2, mapper
  • mapper
public interface UserMapper {
    List<User> getUserInfo(a);
}
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  • mapper.xml

      
<! DOCTYPEmapper
        PUBLIC "- / / mybatis.org//DTD Mapper / 3.0 / EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dbright.mapper.UserMapper">
    <select id="getUserInfo" resultType="com.dbright.pojo.User">
        select * from user
    </select>
</mapper>
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2.3 MyBatis tool class
public class MybatisUtils {

   private static SqlSessionFactory sqlSessionFactory;

   static {
       try {
           String resource = "ContextAplication.xml";
           InputStream inputStream = Resources.getResourceAsStream(resource);
           sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
      } catch(IOException e) { e.printStackTrace(); }}// Obtain the SqlSession connection
   public static SqlSession getSession(a){
       returnsqlSessionFactory.openSession(); }}Copy the code
2.4 Junit test class
  • pom
	<! -- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.1</version>
            <scope>test</scope>
        </dependency>
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  • The test class
public class MyTest {
   @Test
   public void selectUser(a) {
       SqlSession session = MybatisUtils.getSession();
       UserMapper mapper = session.getMapper(UserMapper.class);
       List<User> users = mapper.getUserInfo();
       for(User map: users){ System.out.println(map); } session.close(); }}Copy the code
2.5. Execution result

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