Day14 (3) Mybatis implements CRUD operations based on the agent Dao

Preface

The general implementation interface is to write the implementation class by yourself

public interface MyDao{
    
    
    public void save();
}

//编写实现类文件
public class MyDaoClass implements MyDao{
    
    
    public void save(){
    
    
         System.out.println("Hello");
    }
}

You can also use dynamic agents to help you generate implementation classes in the memory when the program is running.
For example, the **getMapper()** method can help us generate the implementation class.

1. Preparation

1. Write the persistence layer interface: UserDao interface
src\main\java\cn\cyl\dao\UserDao.java

public interface UserDao {
    
    
}

2. Write the mapping configuration of the persistence layer interface: UserDao.xml
src\main\resources\cn\cyl\dao\UserDao.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!--mapper的约束文件-->
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace要求写接口的全类名：包名+类名=全类名-->
<mapper namespace="cn.cyl.dao.UserDao">

</mapper>

3. Configure the mapping in the core configuration file SqlMapConfg.xml file
src\main\resources\SqlMapConfig.xml

<!--配置多个映射文件，告知mybatis映射配置的位置-->
<mappers>
    <mapper resource="UserMapper.xml"/>
    <mapper resource="cn/cyl/dao/UserDao.xml"/>
</mappers>

4. User entity class, user table
src\main\java\cn\cyl\bean\User.java

public class User {
    
    
    private int id;
    private String username;
    private Date birthday;
    private int sex;
    private String address;
    //省略get set toString方法
    }

note:

1. The mapping configuration of the persistence layer interface and the persistence layer interface must be in the same package
   
2. The value of the namespace attribute of the mapper tag in the persistence layer mapping configuration must be the fully qualified class of the persistence layer interface .
3. The id attribute of the configuration tags <select>,<insert>,<delete>,<update> of the SQL statement must be the same as the method name of the persistence layer interface .

Second, query by id

1. Add a method to the UserDao interface

public interface UserDao {
    
    
    User findById(int i);
}

2. UserDao.xml mapping file configuration <select> tag

<mapper namespace="cn.cyl.dao.UserDao">
    <!--使用代理以后，id必须是方法名-->
    <select id="findById" parameterType="int" resultType="cn.cyl.bean.User">
        select * from user where id = #{id};
    </select>
</mapper>

3. Add query test method

@Test
public void selectTest01(){
    
    
    //创建SqlSession对象
    SqlSession sqlSession = MySessionUtils.getSession();
    //getMapper()方法：对你编写的接口使用动态代理技术实现，直接返回实现类对象，即代理对象
        //代理对象的方法内部就是查询sql，并且执行jdbc代码
    //参数：class<T> aClass   
    UserDao dao = sqlSession.getMapper(UserDao.class);
    //定义变量接收
    User user = dao.findById(1);
    //打印结果
    System.out.println(user);
    //释放资源
    sqlSession.close();
}

4. Console output

3. Fuzzy query based on user name

1. Add a method to the UserDao interface

List<User> findByKeyword(String s);

2. UserDao.xml mapping file configuration <select> tag

<select id="findByKeyword" parameterType="string" resultType="User">
    select * from user where username like #{keyword}
</select>

3. Add query test method

@Test
public void selectTest02(){
    
    
    //创建SqlSession对象
    SqlSession sqlSession = MySessionUtils.getSession();
    //返回接口的实现类对象
    UserDao dao = sqlSession.getMapper(UserDao.class);
    //搜索姓张的人
    List<User> list = dao.findByKeyword("张%");
    for (User user:list){
    
    
        System.out.println(user);
    }
    sqlSession.close();
}

4. Console output

Fourth, save users

1. Add a method to the UserDao interface

void saveUser(User user);

2. UserDao.xml mapping file configuration <insert> tag

<insert id="saveUser" parameterType="user">
    insert into user values(null,#{username},#{birthday},#{sex},#{address})
</insert>

3. Add the inserted test method

@Test
    public void insertTest04(){
    
    
        //创建SqlSession对象
        SqlSession sqlSession = MySessionUtils.getSession();
        
        UserDao dao = sqlSession.getMapper(UserDao.class);
        //定义接口
        User user = new User();
//      user.setId(101);
        user.setUsername("jack");
        user.setAddress("北京");
        user.setBirthday(new Date());
	//执行存储方法
        dao.saveUser(user);
	//提交事务
        sqlSession.commit();
        //释放资源
        sqlSession.close();
    }

4. Console output

Five, delete users based on id

1. Add a method to the UserDao interface

void deleteById(int i);

2. UserDao.xml mapping file configuration <delete> tag

<delete id="deleteById" parameterType="int">
    delete from user where id = #{id}
</delete>

3. Add and delete test methods

@Test
public void deleteTest03(){
    
    
    //创建SqlSession对象
    SqlSession sqlSession = MySessionUtils.getSession();
    //返回接口的实现类对象
    UserDao dao = sqlSession.getMapper(UserDao.class);
    //删除id为104的用户
    dao.deleteById(104);
    //提交事务
    sqlSession.commit();
    //释放资源
    sqlSession.close();
}

4. Console output