MyBatis-study notes 01 [01. Mybatis course introduction and environment construction]

• Summary of Java back-end learning route notes [Dark horse programmers]

1. MyBatis-study notes 01 [01. Mybatis course introduction and environment construction] [day01]
2. MyBatis-study notes 02 [02. Mybatis entry case]
3. MyBatis-study notes 03 [03. Customize Mybatis framework]
4. MyBatis-study notes 04 [04. Custom Mybatis framework based on annotation development]
5. MyBatis-study notes 05 [05. Use Mybatis to complete CRUD]
6. ​​​​​​​MyBatis-study notes 06 [06. Use Mybatis to complete the development of the DAO layer]
7. ​​​​​​​MyBatis-study notes 07 [07.Mybatis connection pool and transaction]
8. ​​​​​​​MyBatis-study notes 08 [08. Dynamic SQL]
9. ​​​​​​​MyBatis-study notes 09【09.Multi-table operation of Mybatis】
10. ​​​​​​​MyBatis-study notes 10 [10. JNDI extended knowledge]
11. ​​​​​​​MyBatis-study notes 11 [11. Mybatis cache]
12. ​​​​​​​MyBatis-study notes 12 [12. Mybatis annotation development]

table of Contents

01.mybatis course introduction

02. Correspondence between the three-tier architecture and the ssm framework

03.Analysis of the problem of jdbc operating database

04.mybatis overview

05.mybatis environment construction-preliminary preparation

Create Maven project

Create database table

mybatis coordinates

pom.xml

06.Mybatis environment construction

Write User entity class

Write the persistence layer interface IUserDao

Create a new SqlMapConfig.xml file in the resources folder

Write IUserDao.xml

Summary of steps to build mybatis environment

07. Precautions for environmental construction

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01.mybatis course introduction

Mybatis framework
A total of four days. The
first day: Mybatis introduction
    Mybatis overview
    Mybatis environment to build
    mybatis entry case
    Custom mybatis framework (the main purpose is to let everyone understand the execution details in
mybatis ) Second day: Mybatis basically uses
    the single table of mybatis crud operating
    parameters and return values mybatis
    dao mybatis written
    details mybatis configured
        to use several tags
Day: mybatis in-depth and multi-table
    mybatis connection pooling
    transaction control method and design of mybatis of
    multi-table queries mybatis
        one pair Many (many-to-one)
        many-to-many
Day 4: Mybatis cache and annotation development
    Mybatis loading timing (query timing)
    Mybatis first level cache and second level cache
    Mybatis annotation development
        single-table CRUD
        multi-table query

02. Correspondence between the three-tier architecture and the ssm framework

1. What is a framework?
    It is a set of solutions in our software development, and different frameworks solve different problems.
    The benefits of using the framework: the
        framework encapsulates a lot of details, so that developers can use a minimalist way to achieve functions. Greatly improve development efficiency.
2. Three-tier architecture
    presentation layer:
        the
    business layer for displaying data : the     persistence layer
        for processing business requirements
: it
        interacts with the database

01 three-tier architecture

03.Analysis of the problem of jdbc operating database

3. Persistence layer technology solution
    JDBC technology:
        Connection
        PreparedStatement
        ResultSet
    Spring's JdbcTemplate:
        Simple encapsulation of jdbc in Spring
    Apache's DBUtils:
        It is very similar to Spring's JdbcTemplate, and it is also a simple encapsulation of Jdbc

    These are not frameworks.
        JDBC is a standard
        Spring’s JdbcTemplate and Apache’s DBUtils are just tools.

04.mybatis overview

4. Overview of
    mybatis Mybatis is a persistence layer framework, written in java.
    It encapsulates many details of jdbc operation, so that developers only need to pay attention to the sql statement itself, without having to pay attention to the complicated process of registering drivers, creating connections and so on.
    It uses ORM ideas to achieve the encapsulation of result sets.

    ORM:
        Object Relational Mappging
        Simply put: it
            is to associate the database table with the entity class and the attribute of the entity class
            so that we can operate the database table by operating the entity class.

            user User
            id userId
            user_name userName
    Today we need to
        keep the attributes in the entity class consistent with the field names of the database table.
            user data table User entity class
            id id
            user_name user_name

05.mybatis environment construction-preliminary preparation

Create Maven project

If checked, select ordinary java project

 

Create database table

Database: eesy_mybatis

DROP TABLE IF EXISTS `user`;

CREATE TABLE `user` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(32) NOT NULL COMMENT '用户名称',
  `birthday` datetime default NULL COMMENT '生日',
  `sex` char(1) default NULL COMMENT '性别',
  `address` varchar(256) default NULL COMMENT '地址',
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert into `user`(`id`,`username`,`birthday`,`sex`,`address`) values ​​(41,'Old King','2018-02-27 17:47:08','Male ','Beijing'),(42,'Little Second King','2018-03-02 15:09:37','Female','Beijing Golden Yanlong'),(43,'Little Second King','2018 -03-04 11:34:34','female','Beijing Jinyanlong'),(45,'Chuanzhi Podcast','2018-03-04 12:04:06','male','Beijing Jinyanlong '),(46,'Lao Wang','2018-03-07 17:37:26','Male','Beijing'),(48,'Little Pony','2018-03-08 11:44 :00','Female','Beijing Correction');

mybatis coordinates

mybatis official website: https://mybatis.org/mybatis-3/zh/index.html

​​​​​​​

<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>x.x.x</version>
</dependency>

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.itheima</groupId>
    <artifactId>day01_easy_01mybatis</artifactId>
    <version>1.0-SNAPSHOT</version>
    
    <packaging>jar</packaging><!--打包方式：jar包-->

    <!--导入mybatis坐标-->
    <dependencies><!--依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.6</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.12</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>
</project>

06.Mybatis environment construction

Write User entity class

package com.itheima.domain;

import java.io.Serializable;
import java.util.Date;

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", birthday=" + birthday +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

Write the persistence layer interface IUserDao

package com.itheima.dao;

import com.itheima.domain.User;

import java.util.List;

/**
 * 用户的持久层接口
 */
public interface IUserDao {
    /**
     * 查询所有用户
     *
     * @return
     */
    List<User> findAll();
}

Create a new SqlMapConfig.xml file in the resources folder

SqlMapConfig.xml: The file name is generally written as SqlMapConfig.xml.

<?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">
<!-- mybatis的主配置文件 -->
<configuration>
    <!-- 配置环境 -->
    <environments default="mysql">
        <!-- 配置mysql的环境-->
        <environment id="mysql">
            <!-- 配置事务的类型-->
            <transactionManager type="JDBC"></transactionManager>
            <!-- 配置数据源（连接池） -->
            <dataSource type="POOLED">
                <!-- 配置连接数据库的4个基本信息 -->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/eesy_mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <!-- 指定映射配置文件的位置，映射配置文件指的是每个dao独立的配置文件 -->
    <mappers>
        <mapper resource="com/itheima/dao/IUserDao.xml"/>
    </mappers>
</configuration>

Write IUserDao.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.itheima.dao.IUserDao">
    <!--配置查询所有-->
    <select id="findAll" resultType="com.itheima.domain.User">
        select * from user
    </select>
</mapper>

Summary of steps to build mybatis environment

07. Precautions for environmental construction

Precautions for setting up the environment: The
        first one: when creating IUserDao.xml and IUserDao.java, the names are to be consistent with our previous knowledge.
            In Mybatis, it also calls the operation interface name and mapping file of the persistence layer: Mapper,
            so: IUserDao and IUserMapper are the same. (Mapper==Dao)
        Second: When creating a directory in idea, it is different from a
            package. When the package is created: com.itheima.dao, it is a three-level structure
            directory. When created: com.itheima.dao It is the
        third level of the first-level directory : the location of the mapping configuration file of mybatis must be the same as the package structure of the dao interface. The
        fourth: the value of the namespace attribute of the mapper tag of the mapping configuration file must be the fully qualified class name of the dao interface. The
        fifth: The operation configuration of the mapping configuration file (select), the value of the id attribute must be the method name of the dao interface

        When we comply with the third, fourth, and fifth points, we no longer need to write dao implementation classes in development.