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Discover how to fetch associated records in Rails using ActiveRecord without merging arrays. Learn to create efficient queries for your models.
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This video is based on the question https://stackoverflow.com/q/66971058/ asked by the user 'Mark Denn' ( https://stackoverflow.com/u/339067/ ) and on the answer https://stackoverflow.com/a/66972041/ provided by the user 'Ben Trewern' ( https://stackoverflow.com/u/887947/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Join Two Associations in Rails Without Using Merge

When working with Ruby on Rails, you might commonly encounter scenarios where you need to fetch related records from multiple associations. However, the usual method of merging records may lead to an array, which can complicate further operations like filtering and pagination. In this guide, we'll explore how to join two associations directly in a single ActiveRecord query without resorting to merging, allowing for more efficient data handling in your Rails applications.

The Problem

Imagine you're building a Rails 5.2 application that handles Project objects. Each project can have many Events and Meetings, and both events and meetings have associated CalendarItems. The goal is to retrieve all CalendarItems for a specific Project efficiently as an ActiveRecord relation.

To illustrate, here’s a simplified breakdown of your models:

Project

has many events

has many meetings

Event

has many calendar_items

Meeting

has many calendar_items

CalendarItem

belongs to event

belongs to meeting

When you initially tried obtaining all calendar items with:

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

You ended up with an array. Although it gets the job done, an array prevents you from utilizing further ActiveRecord querying features like filtering and pagination.

The Solution

Instead of merging queries, you can utilize ActiveRecord's joins method to create a more efficient, direct query. This approach will allow you to get an ActiveRecord relation that can be filtered further.

Step-by-Step Breakdown

Understanding the SQL Equivalent: To visualize your desired database query, think about it in SQL terms:

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

Implementing the ActiveRecord Query: You can translate the SQL into an ActiveRecord query within the Project model. Here’s how:

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

In this code:

joins(:event, :meeting) joins the CalendarItems table with both associated events and meetings.

where conditions filter results based on the current project's ID.

Considerations:

This implementation might not have been tested in your particular environment, so it's crucial to perform checks and ensure it behaves as expected.

Ensure your database schema and relationships are correctly set up so that the joins function properly.

Conclusion

Joining associations in Rails without manually merging arrays can enhance the efficiency and usability of your code. By utilizing ActiveRecord’s joins method, you create a dynamic querying capability that allows for further manipulation of the resulting dataset, such as filtering and pagination.

Feel free to adapt the provided solution to fit the specifics of your application, and happy coding!