My colleague told me that the reason why his code is silky is that he uses Mybatis Plus?

1. Pain points of mybatis

We know that MyBatis is a persistence layer framework based on java. It encapsulates jdbc internally, which greatly improves our development efficiency.

However, there are many pain points in developing with Mybatis:

  1. Each Dao interface needs to define a bunch of addition, deletion, modification and query methods.
 * @Desc: UserDao Interface
 * @Author: Official account: know if the technology
 * @date: 7:43 PM 2022 / 5 / 7
public interface UserDao {
    // Get all user information
    List<User> getUserList();
    // Get user information based on id
    User getUserById(int id);
    // New user information
    boolean add(User user);
    // Update user information
    boolean update(User user);
    // Delete user information
    boolean delete(int id);
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2. Each Mapper file needs to write a pile of basic addition, deletion, modification and query statements.

3. If the query list needs paging, we also need to encapsulate the component page object for the query method.

You might say: can Mybatis still hurt? How convenient it is to use!

For small projects, it's OK to use it. However, in case of large projects, there are hundreds of Dao interfaces. If you have to manually define a pile of addition, deletion, modification and query methods and sql statements, it will also be a waste of time.

Is there such a framework:

1. It encapsulates Mybatis and comes with CRUD method. We don't need to define CRUD method ourselves.

2. Provide various query methods without writing some basic sql statements in the mapper file.

3. The paging function is encapsulated to make paging query extremely smooth.

Yes, MybatisPlus is on the stage.

2. Meet MybatisPlus

Official website:
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MybatisPlus is encapsulated based on the original functions of Mybatis. It does not change, but enhances the function of Mybatis.

We don't have to write map XML, directly calling its API can complete CRUD and various query operations.

And it comes with some advanced functions such as paging plug-in, which greatly improves our development efficiency.

3. Introductory cases

Development environment:

  • Development tool: IDEA
  • Build tool: Maven
  • Database: MySQL
  • Project framework: SpringBoot

1. Create a new SpringBoot project

2. Introduce dependency

<!-- mybatis-plus rely on-->
<!-- mysql drive -->
<!-- test -->
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3. Create database table

user table:

  `name` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT 'full name',
  `age` int DEFAULT NULL COMMENT 'Age',
) ENGINE=InnoDB AUTO_INCREMENT=1508421137384648706 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci ROW_FORMAT=DYNAMIC;
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4. Entity class

public class User {
    @TableId(value = "id", type = IdType.ASSIGN_ID)
    private Long id;
    private String name;
    private int age;

    public User(String name, int age) { = name;
        this.age = age;

    public Long getId() {
        return id;

    public void setId(Long id) { = id;

    public String getName() {
        return name;

    public void setName(String name) { = name;

    public int getAge() {
        return age;

    public void setAge(int age) {
        this.age = age;
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5. Modify application yml

  port: 8082
    context-path: /mybatisplus_demo
# Data source configuration
    username: root
    password: 12345678
    url: jdbc:mysql://localhost:3306/ssm?allowPublicKeyRetrieval=true&useSSL=false
    driver-class-name: com.mysql.cj.jdbc.Driver
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6. Create a new UserMapper interface


(1) Because mybatis stipulates: mapper The name of the XML file should be the same as that of the interface, so many people are used to naming the Dao interface xxmapper.

(2)BaseMapper is the built-in interface of MybatisPlus, which contains basic CRUD methods.

7. Add @ MapperScan annotation to the startup class

8. Test

public class MybatisPlusDemoApplicationTests {

    private UserMapper userMapper;

    void testMybatisPlus() {
        for (int i = 18; i < 20; i++) {
            User user = new User("Wang Xiaobo" + i, i);
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9. Summary

We found that as long as we inherit the BaseMapper of MybatisPlus, we can complete the basic addition, deletion, modification and query operations, which is very convenient.

4. Basic addition, deletion, modification and query

1. NEW

User user = new User("Wang Xiaobo", 19);
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2. Editing

Update data according to id

int rows = userMapper.updateById(user);
    System.out.println("Update successful"); 
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3. Delete

Delete information according to primary key

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Delete information according to map conditions

Map<String, Object> param = new HashMap<>();
param.put("age", 18);
int rows = userMapper.deleteByMap(param);
if (rows > 0) {
    System.out.println("Delete succeeded!");
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Batch deletion based on id set

List<Integer> ids = Stream.of(110, 112, 113, 115).collect(Collectors.toList());
int rows = userMapper.deleteBatchIds(ids);
if (rows > 0) {
  System.out.println("Delete succeeded!");
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4. Query

Query by id

User user = userMapper.selectById(152382374);
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Query according to map criteria

Map<String, Object> param = new HashMap<>();
param.put("age", 18);
List<User> userList = userMapper.selectByMap(param);
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Batch query based on id set

List<Integer> ids = Stream.of(110, 112, 113, 115).collect(Collectors.toList());
List<User> userList = userMapper.selectBatchIds(ids);
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5. Constructor

MybatisPlus provides a query constructor and an update constructor to generate sql statements with where conditions.

(1) Constructor encapsulating query criteria:

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Common query criteria:

Equal to: eq

QueryWrapper<User> userWrapper = new QueryWrapper<>();
// Query the user whose name is Zhang San
userWrapper.eq("name","Zhang San");
List<User> userList = userMapper.selectList(userWrapper);
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Not equal to: ne

QueryWrapper<User> userWrapper = new QueryWrapper<>();"name","Zhang San");
// User whose query name is not Zhang San
List<User> userList = userMapper.selectList(userWrapper);
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Fuzzy query: like

QueryWrapper<User> userWrapper = new QueryWrapper<>();
// Fuzzy query"name","Zhang");
List<User> userList = userMapper.selectList(userWrapper);
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Descending order: orderByDesc

QueryWrapper<User> userWrapper = new QueryWrapper<>();
// Fuzzy query and reverse order according to number"name","Zhang").orderByDesc("number");
List<User> userList = userMapper.selectList(userWrapper);
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Ascending order: orderByAsc

QueryWrapper<User> userWrapper = new QueryWrapper<>();
// Fuzzy query and descending order according to number"name","Zhang").orderByAsc("number");
List<User> userList = userMapper.selectList(userWrapper);
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For other common conditions, you can check the relevant documents on the official website, which will not be repeated here:
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(2) Constructor that encapsulates the update condition:

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The where condition of UpdateWrapper is the same as that of QueryWrapper, except that the set value is required.

UpdateWrapper<User> userWrapper = new UpdateWrapper<>();
userWrapper.set("name","Wang Xiaobo").set("age",22)
    .eq("name","Zhang San");
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6. General Service

MybatisPlus has a general interface Iservice and implementation class, which encapsulates common operations such as addition, deletion, modification and query.

1. Create a new service and implementation class


 * @Desc:
 * @Author: Official account: know if the technology
 * @date: 9:57 PM 2022 / 5 / 11
public interface UserService extends IService<User> {

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 * @Desc:
 * @Author: Official account: know if the technology
 * @date: 9:57 PM 2022 / 5 / 11
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {

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2. Test

We found that the IService interface encapsulates some common methods, which greatly improves our development efficiency.

7. Common notes


MybatisPlus will take the id in the entity class as the primary key by default.

@TableId refers to the generation strategy of id. there are two commonly used methods:

(1) Self increment strategy based on Database

(2) Random generation using snowflake algorithm strategy


If the table names of the entity class and the database are inconsistent, you can use this annotation for mapping

For example:


When the table attribute and the attribute name in the entity class are inconsistent, you can use this annotation for mapping:

8. Pagination

The paging plug-in is encapsulated in MybatisPlus, and the paging function can be realized only by simple configuration.

1. Configuration class

 * @Desc:
 * @Author: Official account: know if the technology
 * @date: 9:31 PM 2022 / 5 / 11
public class MybatisPlusConfig {

    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        return interceptor;
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2. Test

void testMybatisPlus() {
    int current = 1;
    int size = 10;
    Page<User> userPage = new Page<>(current, size);
    //Get paging data
    List<User> list = userPage.getRecords();
    Page<User> page = userMapper.selectPage(userPage, null);
    System.out.println("Current page:" + page.getCurrent());
    System.out.println("Number of entries per page:" + page.getSize());
    System.out.println("Total records:" + page.getTotal());
    System.out.println("PageCount :" + page.getPages());
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9. Code generator

MybatisPlus can help us automatically generate controller, service, dao, model and mapper XML and other files, which greatly improves our development efficiency.

1. Introduce dependency

<!-- Code generator  -->
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2. Code generator tool class

public class CodeGenerator {
public static void main(String[] args) {
// Connect database
FastAutoGenerator.create("jdbc:mysql://localhost:3306/ssm?allowPublicKeyRetrieval=true&useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC", "root", "123456")
    .globalConfig(builder -> {"Know technology") // Set author
                .fileOverride() // Overwrite generated files
                // Set date and time
                .outputDir("D:\\WorkSpace\\idea\\mybatisplus_demo\\src\\main\\java"); // Specify output directory
    .packageConfig(builder -> {
        builder.parent("com.zhifou") // Set parent package name
                .pathInfo(Collections.singletonMap(OutputFile.mapperXml, "D:\\WorkSpace\\idea\\mybatisplus_demo\\src\\main\\resources\\mapper")); // Set mapperXml generation path
    .strategyConfig(builder -> {
        builder.addInclude("t_user") // Set the table name to be generated
                .addTablePrefix("t_"); // Before setting filter table

        // Add new data and automatically assign a value to the creation time
        IFill createFill = new Column("created_date", FieldFill.INSERT);
        IFill updateFill = new Column("updated_date", FieldFill.UPDATE);
                // Set id type
                // Open Lombok
                // Turn on continuous setting mode
                // Hump naming mode
                // Automatically assign values to creation time and modification time
                // Delete field logically

        // Restful style
        // Remove Service prefix I
        // mapper settings
    // fixed
    .templateEngine(new FreemarkerTemplateEngine()) // Freemarker engine template is used. The default is Velocity engine template
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Key points:

(1) Configure database connection information.

Automatic code generation requires connection to the database

(2) Specify the output directory. Set the directory of your project directly here. There is no need to assign and paste at that time.

(3) Set the parent package name.

(4) Set table name

Then right-click to run, and the code will be generated automatically.

10. application.yml configuration

# MybatisPlus
      column-underline: true # Hump form
      logic-delete-field: isDeleted # Global logically deleted entity field name
      logic-delete-value: 1 # Logical deleted value (default = 1)
      logic-not-delete-value: 0 # Logical undeleted value (default is 0)
      db-type: mysql
      id-type: assign_id # id policy
      table-prefix: t_ # Default prefix for configuration table 
  mapper-locations: classpath*:/mapper/**Mapper.xml # mapper file location
  type-aliases-package: com.zhifou.entity # Entity class alias
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl # Log: print sql statements
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11. Complete code

Extraction code: 9un7 
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12. Pit encountered

1. When the parameter passed is 0, the query statement is invalid.

For example, if the age passed is 0, the query will become invalid

<select id="getUser" resultType="user">
    select id,name,age,sex from user
        <if test="age != null and age !='' ">
            age = #{age}
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Reason: judge whether int is empty= Null is OK. If you add type! = '', 0 will be made null.

2.MybatisPlus failed to update the field to null

terms of settlement:

@TableField(updateStrategy = FieldStrategy.IGNORED)
private String name;
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This annotation will ignore the judgment that is empty,

Tags: Java Spring Boot Interview Spring Cloud programming language

Posted by greenber on Sun, 15 May 2022 00:18:14 +0300