MyBatis-Plus Tutorial: Creating User Table, Entity, Mapper, and Query Methods

This guide shows how to use MyBatis‑Plus for basic CRUD operations in a Java backend project.

1. Create the User table

The table schema is defined with the following SQL script:

DROP TABLE IF EXISTS user;
CREATE TABLE user (
    id BIGINT(20) NOT NULL COMMENT '主键ID',
    name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
    age INT(11) NULL DEFAULT NULL COMMENT '年龄',
    email VARCHAR(50) NULL DEFAULT NULL COMMENT '邮箱',
    PRIMARY KEY (id)
);

Sample data is inserted with:

DELETE FROM user;
INSERT INTO user (id, name, age, email) VALUES
(1, 'Jone', 18, '[email protected]'),
(2, 'Jack', 20, '[email protected]'),
(3, 'Tom', 28, '[email protected]'),
(4, 'Sandy', 21, '[email protected]'),
(5, 'Billie', 24, '[email protected]');

2. Create the Java entity

package com.example.demo.entity;

import lombok.Data;

@Data
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

3. Create the mapper interface

package com.example.demo.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.demo.entity.User;

public interface UserMapper extends BaseMapper<User> {
}

4. Query methods

4.1 selectList – retrieve all records

@Test
public void testSelect() {
    System.out.println("----- 单表查询所有记录------");
    List<User> userList = userMapper.selectList(null);
    Assert.assertEquals(6, userList.size());
    userList.forEach(System.out::println);
}

Generated SQL:

SELECT id,name,age,email FROM user

4.2 selectById – retrieve a single record by primary key

@Test
public void testSelectById() {
    System.out.println("----- 单表根据主键id查询单条记录 ------");
    User user = userMapper.selectById(2);
    System.out.println(user);
}

Generated SQL:

SELECT id,name,age,email FROM user WHERE id=?

4.3 selectBatchIds – batch query by a list of IDs

@Test
public void testSelectByIds() {
    System.out.println("----- 单表根据 id list 批量查询 ------");
    List<Long> idsList = Arrays.asList(2L,4L,6L);
    List<User> userList = userMapper.selectBatchIds(idsList);
    userList.forEach(System.out::println);
}

Generated SQL:

SELECT id,name,age,email FROM user WHERE id IN ( ?, ?, ? )

4.4 selectByMap – conditional query

@Test
public void testSelectByMap() {
    System.out.println("----- 单表根据条件查询 ------");
    Map<String, Object> conditions = new HashMap<>();
    conditions.put("name", "Jack");
    conditions.put("age", 20);
    List<User> userList = userMapper.selectByMap(conditions);
    userList.forEach(System.out::println);
}

Generated SQL:

SELECT id,name,age,email FROM user WHERE name = ? AND age = ?

The article also includes screenshots, links to related tutorials, and a brief author note, but the core instructional content focuses on setting up the database schema, Java entity, mapper, and demonstrating the four basic query methods provided by MyBatis‑Plus.