Getting started with Mybatis 01

1. Mybatis introduction

Mybatis is a persistence layer framework that supports ordinary SQL queries, stored procedures and advanced mapping. It is a semi-automatic ORM persistence layer framework with high SQL flexibility, supports advanced mapping (one-to-one, one-to-many), dynamic SQL, lazy loading and caching features, but its database independence is low .

JDBC->dbutils->MyBatis->Hibernate

Hibernate is a fully automated framework

2. Mybatis Quick Start

First: add jar package

mysql，mybatis，lombok

Note: lombok: (The lombok plug-in of idea must be installed, which can generate get, set, parameterized and non-parameterized structures of entity classes)

<!--        mysql依赖-->
    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.40</version>
        </dependency>
<!--        mybatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>
<!--        lombok依赖-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.18</version>
        </dependency>

Second: Create a database and table

Facilitate the configuration of mybatis-config.xml

Third: add Mybatis configuration file mybatis-config.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">
<configuration>
    <environments default="development">
        <environment id="development">
         <!--  JDBC：代表使用的事务管理类型，默认打开事务，操作之后需要手动提交-->
            <transactionManager type="JDBC"/>   
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <!--  ppp代表连接数据库的表-->
                <property name="url" value="jdbc:mysql://localhost:3306/ppp"/>
                <!--  username代表数据库的用户名-->
                <property name="username" value="root"/>
                <!--  password代表数据库的密码-->
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

Fourth: Define the entity class corresponding to the table

//以下注解是Lombok中的注解
@Data  （包括get、set、toString）
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private int id;
    private String username;
    private String password;
}

Fifth: Define the CURD (add, delete, modify, and check) operation for operating the user table

sql mapping file UserMapper.xml

note:

resultType: The data type returned after the query statement is executed. The int type can be omitted, and other types cannot be omitted.

parameterType: indicates the type of the passed parameter, the attribute can not be added

namespace: namespace, give a unique name to the container that currently stores mybatis, which must match the full path of the interface

select: indicates the query label: the sql statement for the query can be placed in the label

id: the only sign, the name must be the same as the interface name;

 

<?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">
<!--   namespace必须和接口的全路径匹配-->
<mapper namespace="com.zz.dao.UserDao">
    <!--    id名字必须要跟接口名字一样-->
<!-- select 代表添加的sql   -->
    <select id="selectAll" resultType="com.zz.entity.User">
    select * from user
    </select>
<!-- insert 代表添加的sql   insertUser必须和映射dao接口的方法名一致 -->
    <insert id="insertUser">
        insert into user(username,password) values (#{param1},#{param2})
    </insert>
<!-- update 代表修改的sql   -->
    <update id="updateUser">
        update user set username=#{username},password=#{password} where id=#{id}
    </update>
<!-- delete 代表删除的sql   -->
    <delete id="deleteUser">
        delete from user where id=#{id}
    </delete>
</mapper>

Sixth: Register the userMapper.xml file in the conf.xml file

note:

• The tag of mappers should be placed in <configuration></configuration>
• resource="mapper path" For example: resource="mapper\UserMapper.xml"

 <mappers>
        <mapper resource="mapper\UserMapper.xml"/>
</mappers>

Seventh: Write test code:

Note: JDBC transaction management opens transactions by default. After adding, deleting and modifying operations, you need to commit the transaction. For example: session.commit();

Ordinary additions, deletions, corrections

For example: haha.selectById

haha: namespace="haha", the name of the mapper.xml namespace

selectById： id="selectById"

1. Inquire

Note: selectOne means only query one

selectList() indicates that the query is a list collection type.

 

  public static void main(String[] args) throws Exception {
//        查询
//加载 mybatis 的配置文件（它也加载关联的映射文件）
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
//构建 sqlSession 的工厂
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//创建能执行映射文件中 sql 的 sqlSession
        SqlSession session = sessionFactory.openSession();
//        执行sql   haha：命名空间的名字
        User user = session.selectOne("haha.selectById", 2);
        System.out.println(user);
    }

2. Add

insert means adding method

 

 

  //    添加
    @Test
    public void insert() throws Exception {
//        1.读取mybatis-config.xml
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
//        2.读取sqlSessionFaction
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//        3.获取sqlSession对象
        SqlSession session = sessionFactory.openSession();
//        4.执行sql
        int insert = session.insert("haha.insertUser", new User("峥峥", "111"));
//        增删改需要提交事务
        session.commit();
        System.out.println(insert);

    }

3. Modify

update means the method of modification

 

    //修改
    @Test
    public void update() throws Exception {
//添加mybatis-config.xml
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
//      获取sqlSessionFactory
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//        读取sqlSession对象
        SqlSession session = sessionFactory.openSession();
        int update = session.update("haha.updateUser", new User(3, "李四", "333"));
//执行sql
        session.commit();
        System.out.println(update);

    }

4. Delete

delete means delete method

 

//    删除
    @Test
    public void delete() throws Exception{
//      1.  添加mybatis-config.xml
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
//    2 获取·sqlSessionFactory
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//        3 读取sqlSession对象 执行sql语句
        SqlSession session = sessionFactory.openSession();
//        4.执行sql
        int delete = session.delete("haha.deleteUser", 2);
//        5 提交事务
        session.commit();
        System.out.println(delete);

    }

Operation in actual development:

Note: In actual development, the interface should be used in conjunction with the mapping file

1. The created interface userDao

 

public interface UserDao {
    /**
     * 查询所有的用户信息
     * @return返回所有的用户信息
     */
    List<User> selectAll();
/**
 * 添加用户信息
 */
    int insertUser(String username,String password);
    /**
     * 修改用户信息
     */
    int updateUser(User user);

    /**
     * 删除用户信息
     */
    int deleteUser(int id);
}

2. Create the mapped file

 

<?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">
<!--   namespace必须和接口的全路径匹配-->
<mapper namespace="com.zz.dao.UserDao">
    <!--    id名字必须要跟接口名字一样-->
    <select id="selectAll" resultType="com.zz.entity.User">
    select * from user
    </select>
    <insert id="insertUser">
        insert into user(username,password) values (#{param1},#{param2})
    </insert>
    <select id="selectByuserAndpwd" resultType="com.zz.entity.User">
        select * from user where username=#{username} and password=#{password}
    </select>
    <update id="updateUser">
        update user set username=#{username},password=#{password} where id=#{id}
    </update>
    <delete id="deleteUser">
        delete from user where id=#{id}
    </delete>
</mapper>

3. Adding, deleting and modifying operations in actual development

• Execute the defined select statement

  /**
     * 查询全部
     * @throws Exception
     */
    @Test
    public void select()throws Exception{
//        先读取mybatis-config.xml
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
//        获取sqlSessionFactory
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//        读取sqlSession对象
        SqlSession session = sessionFactory.openSession();
//      得到对应接口的实现类
        UserDao mapper = session.getMapper(UserDao.class);
        List<User> users = mapper.selectAll();
//        提交事务
        session.commit();
        System.out.println(users);
    }

• Execute the defined insert statement

 

 //    添加用户
    public static void main(String[] args) throws Exception{
//        1.先获取mybatis-config.xml
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
//    2.获取sqlSessionFactory
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//        3 读取sqlSession对象 执行sql语句
        SqlSession session = sessionFactory.openSession();
//        4.执行sql
        UserDao userDao = session.getMapper(UserDao.class);//获得对应接口的实现类
        int i = userDao.insertUser("峥11", "11111");
        session.commit();
        System.out.println(i);
    }

• Execute the defined update statement

   /**
     * 修改
     * @throws Exception
     */
    @Test
    public void update() throws Exception{
//        先读取mybatis-config.xml
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
//        获取sqlsessionFactory
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//        读取sqlSessiom对象
        SqlSession session = sessionFactory.openSession();
//        得到对应的实现类
        UserDao userDao = session.getMapper(UserDao.class);
        int i = userDao.updateUser(new User(4, "哈哈哈", "222"));
//        提交事务
        session.commit();
        System.out.println(i);
    }

• Execute the defined delete statement

/**
     * 删除
     * @throws Exception
     */
    @Test
    public void delete() throws Exception{
//        读取mybatis-config.xml
        Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
//        获取sqlSessionFaction
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//       获取到sqlSession对象
        SqlSession session = sessionFactory.openSession();
//        获取到接口对应的实现类
        UserDao mapper = session.getMapper(UserDao.class);
        int i = mapper.deleteUser(5);
        session.commit();
        System.out.println(i);
    }

Precautions

Mismatch may occur in the mapper.xml mapping to the dao layer

The first:

Adding @param to UserDao means to use the name of the parameter as the parameter name of the mapping file

UserMapper.xml: mapper.xml mapping

 

The second type:

UserMapper.xml: mapper.xml mapping

UserDao medium dao layers