1. C2C mode (Consumer To Consumer platform mode)

User to user, the essence of this model is to resell their own traffic or users to video or live content providers, and make profits by selling content.

The platform model avoids very heavy content and services and expands rapidly, but in fact, this model also has defects. The development of online education in the past two years has devalued the content rapidly, making it difficult to bring more free users and traffic.

Representative website:

51cto http://edu.51cto.com/

Tencent classroom https://ke.qq.com/

2. B2C mode (Business To Customer member mode) is the mode used this time

Merchants to users, this mode is to make a large number of videos with their own copyright and put them on their own platform, so that users can pay monthly or annual fees. This model is simple and fast. It can develop rapidly as long as you concentrate on recording a large number of videos. It was hot because of lynda's sky high financing. However, in China, due to weak awareness of copyright protection, easy reproduction of educational content and many competitors with massive free resources, it is difficult to obtain decent cash flow.

 

Representative website:

lynda https://www.lynda.com/

Muke network https://www.imooc.com/

Grain College http://www.gulixueyuan.com/

3. B2B2C (merchant to merchant to user)

The platform links third-party educational institutions and users. Generally, the platform does not directly provide course content, but more undertakes the role of Internet carrier of education, providing all-round support and services for all links of the teaching process.

 

Representative website:

51cto http://edu.51cto.com/

Tencent classroom https://ke.qq.com/

4. Vertical field

This mode requires a combination of recording, broadcasting, live broadcasting, help services and other means to be responsible for students' learning a certain content. This model has high charges and strong barriers. Once this product forms a reputation, it will have a stable user base and income, but the product is very complex, difficult and high threshold. Even a single project will consume a lot of human and material resources, so the development speed is slow.

Representative website:

51cto micro position http://edu.51cto.com/

Micro specialty of Netease cloud classroom https://study.163.com/

5. Live broadcast and interaction

This model moves the feedback, interaction and Q & A in the traditional classroom online. It is easy for users to accept. As long as the service is considerate, users are willing to pay, so they have rich cash flow. However, the defect is that users can only be attracted through the platform, resulting in a low threshold for competition,    The model is the same, there are many competitors, and the revenue is always a large platform with traffic or users.

Representative website:

Special note:

The only supported data types are int, integer, long, long, date, timestamp and localdatetime

Integer type: newVersion = oldVersion + 1

newVersion will write back   entity   in

Only supported   updateById(id)   And   update(entity, wrapper)   method

stay   update(entity, wrapper)   Under the method,   wrapper   Cannot reuse!!!

(4) Register the Bean in MybatisPlusConfig and use the optimistic lock plug-in

@EnableTransactionManagement
@Configuration
@MapperScan("com.yy.mybatisplus.mapper")
public class MybatisPlusConfig {
    //Optimistic lock plug-in
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor() {
        return new OptimisticLockerInterceptor();
    }
}

(5) The test lock can be modified successfully

After the test, analyze the printed sql statement and add 1 to the value of version

   @Test
    void testOptimisticLocker(){
       //query
       User user = userMapper.selectById(1364080977348956166L);
        //Modify data
       user.setName("Helen Yao");
       user.setEmail("helen@qq.com");
        //Execute update
       userMapper.updateById(user);
   }

 ( 6) Test lock modification failed

	//Test lock modification failed
    @Test
    public void testOptimisticLockerFail() {
        //query
        User user = userMapper.selectById(1L);
        //Modify data
        user.setName("Helen Yao1");
        user.setEmail("helen@qq.com1");
        //After the simulation fetches the data, the actual version data in the database is larger than the fetched value, that is, the version has been modified and updated by other threads
        user.setVersion(user.getVersion() - 1);
        //Execute update
        userMapper.updateById(user);
    }

  3.select operation

1. Query records by id

@Test
void testSelectById(){
    User user = userMapper.selectById(1);
    System.out.println(user);
}

2. Batch query through multiple IDS

The foreach function of dynamic sql is completed

//Batch query of multiple IDS
@Test
void testSelectBatchIds(){
    //Batch query data through collection
    List<User> users = userMapper.selectBatchIds(Arrays.asList(1, 2, 3));
    users.forEach(System.out::println);
}

3. Simple conditional query

Encapsulate query criteria through map

Note: the key in the map corresponds to the column name in the database. For example, database user_id, and the entity class is userId. In this case, the key of map needs to be filled in user_id

@Test
void testSelectByMap(){
    HashMap<String, Object> map = new HashMap<>();
    map.put("name","Tester");
    map.put("age",18);
    List<User> users = userMapper.selectByMap(map);
    users.forEach(System.out::println);
}

4. Pagination

MyBatis Plus comes with a paging plug-in, which can realize paging function with simple configuration

(1) Create configuration class

At this point, you can delete the @ MapperScan scan annotation in the main class

//Paging plug-in
@Bean
public PaginationInterceptor paginationInterceptor() {
    return new PaginationInterceptor();
}

(2) Test selectPage paging

Test: finally obtain relevant data through the page object

//Paging query
@Test
void testPage(){
    //1. Create page object
    //Incoming parameters: current page and number of records displayed per page
    Page<User> userPage = new Page<>(1,3);
    //Call mp paging query method
    //In the process of calling mp paging query, the bottom layer will encapsulate and sub load all paging data into the page object
    userMapper.selectPage(userPage,null);

    //Get data through page object
    userPage.getRecords().forEach(System.out::println);//Traverse the paged data of the query
    System.out.println(userPage.getCurrent());//Get current page
    System.out.println(userPage.getSize());//Number of records per page
    System.out.println(userPage.getTotal());//Total records
    System.out.println(userPage.getPages());//PageCount 

    System.out.println(userPage.hasNext());//Determine whether there is a next page
    System.out.println(userPage.hasPrevious());//Determine whether there is a previous page
}

(3) Test selectMapsPage paging: the result set is Map

Note: this line must use mapIPage to obtain the record list, otherwise there will be data type conversion errors

//Test selectMapsPage paging: the result set is Map
@Test
void testSelectMapsPage(){
    //1. Create page object
    //Incoming parameters: current page and number of records displayed per page
    Page<User> page = new Page<>(1,3);
    //Call mp paging query method
    //In the process of calling mp paging query, the bottom layer will encapsulate and sub load all paging data into the page object
    IPage<Map<String, Object>> mapIPage = userMapper.selectMapsPage(page, null);

    //Note: this line must use mapIPage to obtain the record list, otherwise there will be data type conversion errors
    mapIPage.getRecords().forEach(System.out::println);
    System.out.println(page.getCurrent());
    System.out.println(page.getPages());
    System.out.println(page.getSize());
    System.out.println(page.getTotal());
    System.out.println(page.hasNext());
    System.out.println(page.hasPrevious());
}

5.delete operation

1. Delete record by id

@Test
public void testDeleteById(){
    int result = userMapper.deleteById(1364080977348956166L);
    System.out.println(result);
}

2. Batch deletion

@Test
public void testDeleteBatchIds() {
    int result = userMapper.deleteBatchIds(Arrays.asList(8, 9, 10));
    System.out.println(result);
}

3. Simple conditional query deletion

@Test
public void testDeleteByMap() {
    HashMap<String, Object> map = new HashMap<>();
    map.put("name", "Helen");
    map.put("age", 18);
    int result = userMapper.deleteByMap(map);
    System.out.println(result);
}

4. Logical deletion

Physical delete: real delete, delete the corresponding data from the database, and then query the deleted data

Logical deletion: false deletion. Change the status of the field representing whether to be deleted in the corresponding data to deleted status. After that, you can still see this data record in the database

(1) Add deleted field to database

ALTER TABLE `user` ADD COLUMN `deleted` boolean

(2) Add deleted field to entity class
And add  @ TableLogic   Notes and  @ TableField(fill = FieldFill.INSERT)   annotation  

    @TableField(fill = FieldFill.INSERT_UPDATE)
    @TableLogic
    private Boolean isDeleted;

(3) Add the deleted insert default value to the meta object processor interface

@Override
public void insertFill(MetaObject metaObject) {
......
this.setFieldValByName("deleted", 0, metaObject);
}

(4) application.properties add configuration

mybatis-plus.global-config.db-config.logic-delete-value=1
mybatis-plus.global-config.db-config.logic-not-delete-value=0

(5) Register beans in MybatisPlusConfig

@Bean
public ISqlInjector sqlInjector() {
return new LogicSqlInjector();
}

(6) Test logical deletion

/**
* Test logical deletion
*/ 
@Test
public void testLogicDelete() {
int result = userMapper.deleteById(1L);
System.out.println(result);
}

(7) Query after test logic deletion

The query operation in MyBatis Plus will also automatically add the judgment of logically deleting fields

/**
* Query after test logic deletion:
* Records deleted logically are not included
*/
@Test
public void testLogicDeleteSelect() {
User user = new User();
List<User> users = userMapper.selectList(null);
users.forEach(System.out::println);
}

6. Performance analysis plug-in

Performance analysis interceptor, which is used to output each SQL statement and its execution time

SQL performance analysis is performed, the development environment is used, and it stops running after the specified time. Help identify problems

1. Configure plug-ins

1) Parameter description

Parameter: maxTime: the maximum SQL execution time, which exceeds the automatic stop, helps to find problems.

Parameter: Format: whether to format SQL. The default is false.

2) Configuration in MybatisPlusConfig: used in development environment, not recommended online.

//Performance analysis plug-in
/**
 * SQL Execute performance analysis plug-in
 * It is not recommended to use the development environment online. maxTime refers to the maximum sql execution time
 */
@Bean
@Profile({"dev","test"})// Set dev test environment on
public PerformanceInterceptor performanceInterceptor() {
    PerformanceInterceptor performanceInterceptor = new PerformanceInterceptor();
    performanceInterceptor.setMaxTime(100);//ms. if the ms set here is exceeded, sql will not be executed
    performanceInterceptor.setFormat(true);
    return performanceInterceptor;
}

3) Set dev environment in Spring Boot

#Environment settings: dev, test, prod
spring.profiles.active=dev

You can create different profiles for each environment

Just configure the startup environment in application.yml, as in 3)

2. Testing

  1) Routine test

/**
* Test performance analysis plug-in
*/
@Test
public void testPerformance() {
User user = new User();
user.setName("I am Helen");
user.setEmail("helen@sina.com");
user.setAge(18);
userMapper.insert(user);
}

  2) Test again after reducing maxTime

performanceInterceptor.setMaxTime(5);//ms, if it exceeds the ms set here, it will not be executed 

If the execution time is too long, an exception will be thrown: The SQL execution time is too large,

7. Others  

If you want to query complex conditions, you need to use the condition constructor Wapper, which involves the following methods

1,delete

2,selectOne

3,selectCount

4,selectList

5,selectMaps

6,selectObjs

7,update

6, MyBatisPlus condition constructor [wapper]

1. Introduction to wapper

 

Wrapper: conditional construction abstract class, topmost parent class

AbstractWrapper: used to encapsulate query conditions and generate where conditions for sql. QueryWrapper: Entity object encapsulates operation class instead of lambda syntax UpdateWrapper: Update condition. It is used for Entity object Update operation

AbstractLambdaWrapper: Lambda syntax uses Wrapper to handle and parse Lambda to obtain column. LambdaQueryWrapper: it can be understood from the name. It is the query Wrapper used for Lambda syntax. Lambdaupdatewrapper: Lambda update Wrapper

2,AbstractWrapper

Note: the column s in the method input parameters of the following condition constructor represent database fields

1,ge,gt,le,lt,isNull,isNotNull

See the official website for details: https://mp.baomidou.com/guide/crud-interface.html#service-crud-%E6%8E%A5%E5%8F%A3

@Test
public void testDelete() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper
.isNull("name")
.ge("age", 12)
.isNotNull("email");
int result = userMapper.delete(queryWrapper);
System.out.println("delete return count = " + result);
}

UPDATE user SET deleted=1 WHERE deleted=0 AND name IS NULL AND age >= ? AND email IS NOT NULL

2,eq,ne

Note: seletOne returns an entity record. If there are multiple records, an error will be reported

@Test
public void testSelectOne() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.eq("name", "Tom");
    User user = userMapper.selectOne(queryWrapper);
    System.out.println(user);
}

The executed sql statement is

SELECT id,name,age,email,create_time,update_time,version,deleted FROM user WHERE deleted=0 AND name = ?

3,between,notBetween

Include size boundary

@Test
public void testSelectCount() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.between("age", 20, 30);
Integer count = userMapper.selectCount(queryWrapper);
System.out.println(count);
}

The executed sql statement is

SELECT COUNT(1) FROM user WHERE deleted=0 AND age BETWEEN ? AND ?

4,allEq

@Test
public void testSelectList() {
QueryWrapper<User> queryWrapper = new QueryWrapper<>();
Map<String, Object> map = new HashMap<>();
map.put("id", 2);
map.put("name", "Jack");
map.put("age", 20);
queryWrapper.allEq(map);
List<User> users = userMapper.selectList(queryWrapper);
users.forEach(System.out::println);
}

The executed sql statement is

SELECT id,name,age,email,create_time,update_time,version,deleted FROM user WHERE deleted=0 AND name = ? AND id = ? AND age = ?

5,like,notLike,likeLeft,likeRight

selectMaps returns a list of Map collections

@Test
public void testSelectMaps() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper
        .notLike("name", "e")
        .likeRight("email", "t");
    List<Map<String, Object>> maps = userMapper.selectMaps(queryWrapper);//The return value is the Map list
    maps.forEach(System.out::println);
}

The executed sql statement is

SELECT id,name,age,email,create_time,update_time,version,deleted FROM user WHERE deleted=0 AND name NOT LIKE ? AND email LIKE ?

6,in,notIn,inSql,notinSql,exists,notExists

in,notIn:

notIn("age",{1,2,3})—>age not in (1,2,3)

notIn("age", 1, 2, 3)—>age not in (1,2,3)

inSql, notinSql: sub query can be implemented

Example: inSql("age", "1,2,3,4,5,6") - > age in (1,2,3,4,5,6)

Example: inSql("Id", "select id from table where id < 3") - > ID in (select id from table where id < 3)
 

@Test
public void testSelectObjs() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    //queryWrapper.in("id", 1, 2, 3);
    queryWrapper.inSql("id", "select id from user where id < 3");
    List<Object> objects = userMapper.selectObjs(queryWrapper);//The return value is the Object list
    objects.forEach(System.out::println);
}

The sql is:

SELECT id,name,age,email,create_time,update_time,version,deleted FROM user WHERE deleted=0 AND id IN (select id from user where id < 3)

7,or,and

Note: the UpdateWrapper is used here

If you do not call or, and is used by default

@Test
public void testUpdate1() {
    //Modify value
    User user = new User();
    user.setAge(99);
    user.setName("Andy");
    //modify condition
    UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
    userUpdateWrapper
    .like("name", "h")
    .or()
    .between("age", 20, 30);
    int result = userMapper.update(user, userUpdateWrapper);
    System.out.println(result);
}

sql statement:

UPDATE user SET name=?, age=?, update_time=? WHERE deleted=0 AND name LIKE ? OR age BETWEEN ? AND ?

8. Nested or, nested and

lambda expressions are used here, and the expressions in or are finally translated into sql with parentheses

@Test
public void testUpdate2() {
    //Modify value
    User user = new User();
    user.setAge(99);
    user.setName("Andy");
    //modify condition
    UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
    userUpdateWrapper
        .like("name", "h")
        .or(i -> i.eq("name", "Li Bai").ne("age", 20));
    int result = userMapper.update(user, userUpdateWrapper);
    System.out.println(result);
}

sql statement:

UPDATE user SET name=?, age=?, update_time=? WHERE deleted=0 AND name LIKE ? OR ( name = ? AND age <> ? )

9,orderBy,orderByDesc,orderByAsc

@Test
public void testSelectListOrderBy() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.orderByDesc("id");
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);
}

sql:

SELECT id,name,age,email,create_time,update_time,version,deleted FROM user WHERE deleted=0 ORDER BY id DESC

10,last

Directly spliced to the end of sql

Note: it can only be called once. The last call shall prevail. There is a risk of sql injection. Please use it with caution

@Test
public void testSelectListLast() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.last("limit 1");
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);
}

sql:

SELECT id,name,age,email,create_time,update_time,version,deleted FROM user WHERE deleted=0 limit 1

11. Specify the columns to query

@Test
public void testSelectListColumn() {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.select("id", "name", "age");
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);
}

sql:

SELECT id,name,age FROM user WHERE deleted=0

12,set,setSql

The final sql will merge the fields in user.setAge(), userUpdateWrapper.set() and setSql()

@Test
public void testUpdateSet() {
    //Modify value
    User user = new User();
    user.setAge(99);
    //modify condition
    UpdateWrapper<User> userUpdateWrapper = new UpdateWrapper<>();
    userUpdateWrapper
    .like("name", "h")
    .set("name", "Lao Li Tou")//In addition to querying, you can also use set to set the modified fields
    .setSql(" email = '123@qq.com'");//Can have subqueries
    int result = userMapper.update(user, userUpdateWrapper);
}

sql:

UPDATE user SET age=?, update_time=?, name=?, email = '123@qq.com' WHERE deleted=0 AND name LIKE ?