1. MybatisPlus

As always, the most important official documents are out first!
Official documents

1. Import dependency

       <!--mysql-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.17</version>
        </dependency>

        <!--lombok-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <!--mybatis plus-->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.0.5</version>
        </dependency>

2. Configuration yml file

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/niit_test?characterEncoding=utf-8&serverTimezone=GMT
    username: root
    password: yts520..

Note the version of MySQL here.

3. Write corresponding layer code

3.1 User entity class

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {

    private int id;
    private String username;
    private String pwd;
    private String url;
}

3.2 dao

@Mapper
public interface UserMapper extends BaseMapper<User> {
}

Here we directly inherit BaseMapper. There are already basic and commonly used CRUD methods in it. We don't need to write them again.

3.3 startup

@MapperScan("com.niit.mybatisplus.dao")

Add the annotation MapperScan. Note that the scanning path cannot be wrong.

3.4 test

@SpringBootTest
class MybatisplusApplicationTests {

    @Autowired
    private UserMapper userMapper;

    @Test
    void getUsers() {
        List<User> users = userMapper.selectList(null);
        users.forEach(System.out::println);
    }

}

4. Configure log

Easy to view code

Add in the yml file:

#Log configuration
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

5. CRUD extension

5.1 insertion

class MybatisplusApplicationTests {

    @Autowired
    private UserMapper userMapper;
    //insert
    @Test
    public void insterUser(){
        User user = new User();
        user.setUsername("Yu Tiansong");
        user.setPwd("123321");
        user.setUrl("www.baidu.com");
        user.setTencentcondition(1);

        int insert = userMapper.insert(user);
        System.out.println(insert);
        System.out.println(user);
    }

The ID is automatically generated

5.2 primary key generation strategy

Globally unique ID of distributed system:

Snowflake (snowflake algorithm) scheme

Primary key auto increment

1. You need to add @ TableId(type = IdType.AUTO) to the entity class field
2. The primary key id in the database must be self incremented

AUTO(0),NONE(1),INPUT(2),ID_WORKER(3),UUID(4),ID_WORKER_STR(5);

5.3 update

    //Update @ test public void updateuser() {usermapper. Updatebyid (new user (3L, "peach");}

Mybatis plus automatically configures dynamic SQL.

5.4 automatic filling

Creation time and modification time! These operations are completed automatically. We don't want to update them manually!
Alibaba Development Manual: all database tables: gmt_create, gmt_modified almost all tables should be configured! And need automation!

Database (not recommended)

1. Add field create_time, update_time

   Default CURRENT_TIMESTAMP

2. Add attributes to the corresponding entity class

code implementation

Add padding to fields

@TableField(fill = FieldFill.INSERT)private Date createTime;@TableField(fill = FieldFill.INSERT_UPDATE)private Date upDateTime;

5.5 optimistic lock and pessimistic lock

Optimistic lock:

As the name suggests, it is very optimistic. It always thinks that there will be no problems, so it won't lock it. If a problem occurs, update the test again.

Pessimistic lock: hence the name Siyi is very pessimistic. It always thinks that there is always a problem and it will lock no matter what it does! Do it again!

Test:

1. Add the optimistic lock version field to the database

2. The default is 1

3. Add the corresponding attribute in the entity class

4. Register components

   @MapperScan("com.niit.mybatisplus.dao")@EnableTransactionManagement //Automatic management of things @ Configuration / / Configuration class public class MybatisPlusConfig {/ / register optimistic lock plug-in @ bean public optimizationlockerinterceptor optimizationlockerinceptor() {return new optimizationlockerinceptor();}}
   

   UPDATE user SET username=?, pwd=?, url=?, tencentcondition=?, version=?, create_time=?, update_time=? WHERE id=? AND version=? 
   

5. test

       //Optimistic lock - success case @ test public void versiondemo() {user user = usermapper.selectbyid (4); user.setusername ("optimistic lock test 2"); usermapper.updatebyid (user);}
   

       //Optimistic lock - failure case @ test public void versiondemo2() {/ / normal thread user user = usermapper.selectbyid (4); user.setusername ("optimistic lock test - normal"); / / queue cutting thread user user2 = usermapper.selectbyid (4); user2.setusername ("optimistic lock test - queue cutting"); userMapper.updateById(user2);        userMapper.updateById(user);// If there is no optimistic lock, the updated value of queue jumping thread lock will be overwritten}
   

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5.6 query

    //Query @ test void getusers() {list < user > users = usermapper. Selectlist (null); users. Foreach (system. Out:: println);}

Paging query:

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5.7 deletion

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Logical deletion

Physical delete: delete directly from the database

Logical deletion: it is not deleted in the database, but invalidated by a variable!

Logical deletion prevents data loss, similar to putting it in the recycle bin of the computer.

How to use (steps from official documents):

# Step 1: configure com baomidou. mybatisplus. core. config. GlobalConfig$DbConfig

• Example: application yml

mybatis-plus:  global-config:    db-config:      logic-delete-field: flag  # Global logically deleted entity field name(since 3.3.0,Step 2 can be ignored after configuration)      logic-delete-value: 1 # Logical deleted value(The default is 1)      logic-not-delete-value: 0 # Logical undeleted value (0 by default)

# Step 2: add @ TableLogic annotation to the entity class field

@TableLogicprivate Integer deleted;

Execute delete statement

//Delete @ testvoid deleteuser() {usermapper. Deletebyid (4);}

You can see:

==> Preparing: UPDATE user SET deleted=1 WHERE id=? AND deleted=0
> Parameters: 4(Integer)
< Updates: 1

It essentially executes an update statement!!

The data in the database is not deleted, but the deleted value is updated. 1 indicates that it has been deleted logically!

Now let's execute the query statement to see if we can query the data with id 4:

You can see that there is no data with id 4 in the query result!

5.8 performance analysis plug-in

Slow sql encountered. MP also provides a method to stop the query beyond the set time.

Remember to configure the environment in SpringBoot as dev or test environment!

5.9 conditional constructor

official: https://mp.baomidou.com/guide/wrapper.html#abstractwrapper

6. Code generator

I haven't done it yet. It's updated separately

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