Adding MyBatis-Plus Dependency

Include the starter in your Maven project, ensuring version compatibility with your Spring Boot and MyBatis release:

<dependency>
  <groupId>com.baomidou</groupId>
  <artifactId>mybatis-plus-boot-starter</artifactId>
  <version>3.4.1</version>
</dependency>

Defining Entities and Maping Rules

Create a domain class and use Lombok to reduce boilerplate. The framework automatically applies camel‑case to underscore conversion for table and column names. You can enforce this with the following YAML setting:

mybatis-plus:
  configuration:
    map-underscore-to-camel-case: true

Annotation Overrides

• @TableName specifies the database table name.
• @TableField maps a property to a column (value), marks it as non‑persistent (exist = false), or excludes it from SELECT queries (select = false).
• @TableId designates the primary key.

Example:

@Data
@TableName("employee")
public class Employee {
    @TableId
    private Long id;
    private String loginName;
    @TableField("pwd_hash")
    private String passwordHash;
    private Integer experience;
    private String contactEmail;
    @TableField(exist = false)
    private boolean workingRemotely;
}

Here Employee maps to table employee, loginName becomes login_name, and passwordHash maps to the explicit column pwd_hash. The workingRemotely field is ignored during persistence.

Mapper Interface and Base Methods

Define a mapper by extending BaseMapper:

@Mapper
public interface EmployeeDao extends BaseMapper<Employee> {}

This gives you ready‑to‑use CRUD operations:

• int insert(T entity) — inserts a record; nullable properties become null in the database.
• int updateById(T entity) — updates by primary key.
• T selectById(Serializable id) — retrieves a single record.
• List<T> selectBatchIds(Collection<? extends Serializable> ids) — batch fetch by IDs.
• List<T> selectByMap(Map<String, Object> map) — query by column-value pairs.
• List<T> selectList(Wrapper<T> wrapper) — conditional query.
• Integer selectCount(Wrapper<T> wrapper) — count records.
• IPage<T> selectPage(IPage<T> page, Wrapper<T> wrapper) — paginated query.
• List<Map<String, Object>> selectMaps(Wrapper<T> wrapper) — returns result as maps.

Configuring Logging and Banner

Enable SQL statement logging in application.yml:

mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  global-config:
    banner: false

To suppress excessive logging from other components, place an empty logback.xml in src/main/resources:

<?xml version="1.0" encoding="UTF-8"?>
<configuration></configuration>

Building Queries with Wrappers

QueryWrapper

Use equality, range, and pattern-matching methods:

QueryWrapper<Employee> qw = new QueryWrapper<>();
qw.eq("experience", 5)
  .like("contact_email", "@company.com");
List<Employee> result = employeeDao.selectList(qw);

LambdaQueryWrapper

Avoid string‑based column names for type safety:

LambdaQueryWrapper<Employee> lqw = new LambdaQueryWrapper<>();
lqw.ge(Employee::getExperience, 3)
   .le(Employee::getExperience, 10)
   .eq(Employee::getWorkingRemotely, true);
List<Employee> employees = employeeDao.selectList(lqw);

Multiple conditions are combined with AND by default. Use or() to switch to OR:

lqw.lt(Employee::getExperience, 2)
   .or()
   .gt(Employee::getExperience, 12);

Ordering can be added with orderByAsc / orderByDesc. For pagination, pass a Page object together with a wrapper to selectPage.