What is the principle behind Mybatis PageHelper paginat…

MyBatis PageHelper is an open-source pagination plugin that intercepts SQL statements and automatically adds pagination-related SQL statements based on the original SQL statement, achieving physical pagination in the database.

The principle of PageHelper can be briefly summarized in the following steps:

1. Before executing the SQL statement, PageHelper will first call the intercept method of the PageInterceptor interceptor.
2. In the intercept method, PageInterceptor will parse the pagination parameters in the current thread context, including the page number and the number of records displayed per page.
3. PageInterceptor calculates the pagination information, such as the starting row number and ending row number, based on the parsed pagination parameters.
4. Then, PageInterceptor will call different dialect classes (such as MySQLDialect, OracleDialect, etc.) based on the type of database to generate the corresponding pagination SQL statement.
5. The generated pagination SQL statement will be concatenated to the original SQL statement to form a complete pagination query SQL statement.
6. Finally, the PageInterceptor returns the complete paginated SQL query to MyBatis’s executor, which sends it to the database for execution and returns the paginated results.

By following the above steps, PageHelper has implemented the automatic addition of pagination without modifying the original SQL statement. This allows developers to easily implement pagination queries without manually writing complex pagination logic. Additionally, PageHelper also provides some auxiliary methods such as obtaining the current page number, number of records displayed per page, etc., facilitating developers to perform pagination-related operations.