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This article introduces the relevant knowledge of "Mybatis uses collection paging for example analysis". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Reason

The reason for this problem is that when we use the nested result mapping of the ResultMap collection to process the result set queried through join and mapped to the Java entity type, it will cause the master data to be folded by the mapping and less than the data obtained from the database, resulting in less mapping data than per page size of data.

Option one

Instead of using the nested result mapping of the collection, use the nested select query of the collection to solve. Using this scheme requires attention to performance issues, which can lead to "Number1 query problems".

Although this approach is simple, it does not perform well on large datasets or large data tables. This problem is known as the "Number1 query problem". In a nutshell, the Number1 query problem looks like this:

You execute a separate SQL statement to get a list of results (that is, "+ 1"). For each record returned by the list, you execute a select query to load the details (that is, "N") for each record.

This problem can cause hundreds of SQL statements to be executed. Sometimes we don't want to have such consequences.

The good news is that MyBatis can delay loading such queries, so it can spread out the overhead of running a large number of statements at the same time. However, if you iterate through the list of records to get nested data immediately after loading the list, all delayed loading queries will be triggered, and performance may become poor.

Option 2

Remove the collection configuration and process it in the business logic. First, the data participating in paging is obtained, and then the data associated with the paging data is obtained in the business code as needed. Bloggers prefer this solution to solve the collection paging problem in mybatis.

Expansion

There are two ways to load one-to-many relationships in Mybatis:

1. Nested Select queries for collections

A total of two SQL statements are generated, one to query the main data and the other to query the associated data. As follows:

SELECT * FROM BLOG WHERE ID = # {id} SELECT * FROM POST WHERE BLOG_ID = # {id} 2. Nested result mapping of sets

Only one SQL statement is produced, and master data and associated data are configured to map to the properties of their respective objects in the form of aliases. As shown in the play:

This is the end of the content of "example Analysis of Mybatis paging using collection". Thank you for your reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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