Using MyBatis-Plus for CRUD processing in Java API development

As the scale of websites continues to expand, Java developers increasingly need to handle a large number of database operations. Faced with this situation, if you use traditional SQL statements for development, it is easy to have duplicate and redundant code. If you use a framework for development, you can avoid these problems. Among them, MyBatis-Plus is a very popular framework that can be used for CRUD processing in Java API development.

In this article, we will explain in detail how to use MyBatis-Plus for CRUD processing. Specifically, we will discuss how to use MyBatis-Plus for single-table CRUD and multi-table CRUD processing.

Single table CRUD

In single table CRUD processing, we need to first create an entity class, and then map the entity class to the database table. Next, we can use the methods provided by MyBatis-Plus for CRUD processing.

Create entity class

First, we need to create an entity class to save the data we need to operate. In this entity class, it usually contains some basic attributes and some getter and setter methods. The following is an example:

@Data
@TableName("user")
public class User {
    @TableId(type = IdType.AUTO)
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

In this entity class, we use MyBatis-Plus annotations to map table names and primary keys. Among them, the @TableName("user") annotation indicates that the table name corresponding to this entity class is user, and the @TableId(type = IdType.AUTO) annotation Represents the auto-increment type of the primary key.

Use MyBatis-Plus for CRUD processing

Next, we can use the DAO interface provided by MyBatis-Plus for CRUD processing. MyBatis-Plus provides some commonly used CRUD methods, such as insert(), updateById(), selectById() and so on.

@Repository
public interface UserDao extends BaseMapper<User> {
}

In the above example, we only need to inherit the BaseMapper interface to use the CRUD method. Specifically, we can use the insert() method to insert a piece of data:

@Autowired
private UserDao userDao;

public void insertUser(User user) {
    userDao.insert(user);
}

Use the updateById() method to update a piece of data:

public void updateUser(User user) {
    userDao.updateById(user);
}

Use the selectById() method to query a piece of data:

public User selectUserById(Long id) {
    return userDao.selectById(id);
}

Use the deleteById() method to delete a piece of data:

public void deleteUserById(Long id) {
    userDao.deleteById(id);
}

Multi-table CRUD

In addition to single-table CRUD processing, MyBatis-Plus also supports multi-table CRU processing. In multi-table operations, we usually obtain the required data through joint table queries.

Creating entity classes

Different from single-table CRUD, multi-table operations require creating multiple entity classes and establishing relationships between them. Here is an example:

@Data
public class ArticleVO {
    private Long id;
    private String title;
    private String content;
    private List<CommentVO> comments;
}

@Data
public class CommentVO {
    private Long id;
    private String content;
    private Long articleId;
}

In this example, we create two entity classes: ArticleVO and CommentVO. ArticleVO The entity class contains an attribute of type List<CommentVO>, which indicates that one article corresponds to multiple comments.

Use MyBatis-Plus for CRUD processing

In multi-table CRUD processing, we need to use the joint table query method provided by MyBatis-Plus to obtain the required data. MyBatis-Plus provides a selectJoin() method to perform joint table queries.

@Repository
public interface ArticleDao extends BaseMapper<Article> {
    @Select("SELECT a.*, c.id AS comment_id, c.content AS comment_content FROM article a LEFT JOIN comment c ON a.id = c.article_id WHERE a.id = #{id}")
    ArticleVO selectArticleWithCommentsById(Long id);
}

In the above code, we implement the joint table query between ArticleVO and CommentVO through LEFT JOIN. This SQL statement queries all comments corresponding to an article and stores their information in two entity classes: ArticleVO and CommentVO.

Summary

In this article, we explain in detail how to use MyBatis-Plus for single-table CRUD and multi-table CRUD processing. Through the encapsulation of MyBatis-Plus, we can achieve more concise, easy-to-read, and easy-to-maintain code. MyBatis-Plus also has many other features and functions that can help us develop database-related applications more efficiently.

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