Скачать или смотреть Efficiently Select MIN and MAX in One SQL Query with ActiveRecord Scopes

Learn how to select minimum and maximum values from an ActiveRecord scope in a single SQL query, improving efficiency in your Ruby on Rails applications.
---
This video is based on the question https://stackoverflow.com/q/66382558/ asked by the user 'ggsp' ( https://stackoverflow.com/u/2514714/ ) and on the answer https://stackoverflow.com/a/66383591/ provided by the user 'eux' ( https://stackoverflow.com/u/15097028/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Selecting MIN and MAX for a collection, based on an ActiveRecord scope, in one SQL query

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Streamlining SQL Queries in Ruby on Rails: Selecting MIN and MAX Values

If you are a Ruby on Rails developer working with ActiveRecord, you may have encountered scenarios where you need to fetch MIN and MAX values from a database. A common challenge arises when attempting to combine these queries with custom scopes while still keeping your code clean and efficient. This post addresses that specific problem and provides a solution that allows you to utilize chainable scopes without excessive SQL calls or complicated interpolations.

The Challenge

Consider a situation where you want to calculate the minimum and maximum page counts of Book records filtered by certain authors and publishers. Typically, you might write a raw SQL query or run two separate ActiveRecord queries to achieve this, but both methods have drawbacks:

Raw SQL Queries: Tend to lead to messy code with complex interpolations and make maintaining your codebase harder.

Separate Queries: While cleaner, running two separate SQL queries can be less efficient, especially in larger databases or when performance is key.

What You Aim to Achieve

The goal is to fetch the minimum and maximum page counts of books in one SQL query while utilizing the powerful chainability of ActiveRecord scopes. This way, you keep your code elegant and your database queries efficient.

The Solution

To solve this challenge, you can define a class method in your Book model that leverages ActiveRecord's query interface to fetch the desired values. Here’s how you can effectively implement this solution:

Step 1: Define the Class Method

You will create a class method called minmax_page_count in the Book model. This method will use ActiveRecord's select with window functions to calculate the minimum and maximum page counts simultaneously. Here’s the code you will need:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Chain Your Scopes

You can now call this new method after filtering your books with the desired scopes. Instead of writing complex queries or dealing with interpolations, simply do the following:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Interpret the Results

When you run the above code, it will return an array containing the minimum and maximum page counts for the selected books, efficiently executing your query in a single SQL call:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Utilizing the minmax_page_count method in your Book model allows you to seamlessly integrate an efficient solution into your Rails application without sacrificing code quality. You keep the chainable scope feature of ActiveRecord while also minimizing the number of database calls, all in an elegant and maintainable manner.

By following the steps outlined in this post, you can achieve optimal performance and cleaner code in your Ruby on Rails applications. Happy coding!