In-depth discussion of the implementation principle of MyBatis paging plug-in

MyBatis is an open source persistence layer framework that provides an elegant way to manage database access code. In most actual projects, we often use paging queries to perform fast data display when the amount of data is large. In order to facilitate paging queries in MyBatis, we can use the paging plug-in of MyBatis.

1. Introduction of MyBatis paging plug-in

First of all, we need to introduce the MyBatis paging plug-in into the project. You can add the corresponding dependency packages to the project through build tools such as Maven or Gradle:

<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper</artifactId>
    <version>5.1.11</version>
</dependency>

2. Configure the MyBatis paging plug-in

Configure the paging plug-in we introduced in the MyBatis configuration file:

<plugins>
    <plugin interceptor="com.github.pagehelper.PageInterceptor">
        <property name="helperDialect" value="mysql"/>
        <property name="reasonable" value="true"/>
    </plugin>
</plugins>

In the above configuration, we specified the dialect of the paging plug-in as MySQL, and set the reasonable attribute to true, which means that when pageNum is less than 1, the first page is automatically queried, and when it is greater than the total number of pages, the last page is automatically queried. Page.

3. Use the MyBatis paging plug-in

Next, we can declare the method of using the paging plug-in in our Mapper interface:

List<User> selectUsersByPage(int pageNum, int pageSize);

Implement this in the Mapper XML file Method:

<select id="selectUsersByPage" resultType="com.example.User">
    SELECT * FROM user
</select>

4. Call the paging query method in the Service layer

Finally, call the paging query method in the Service layer. The sample code is as follows:

@Service
public class UserService {

    @Autowired
    private UserMapper userMapper;

    public PageInfo<User> getUsersByPage(int pageNum, int pageSize) {
        PageHelper.startPage(pageNum, pageSize);
        List<User> userList = userMapper.selectUsersByPage(pageNum, pageSize);
        return new PageInfo<>(userList);
    }
}

In the above code , we use the PageHelper.startPage method to specify the number of pages for paging and the number of items per page, and then call the selectUsersByPage method in Mapper to perform paging queries, and encapsulate the results as PageInfo objects and return them.

Through the above steps, we have successfully implemented the function of using the paging plug-in for paging query in MyBatis. The paging plug-in can not only simplify the implementation of paging queries, but also improve query efficiency and reduce the pressure on the database. I hope this article can help everyone better understand the implementation principle of the MyBatis paging plug-in.

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