Resolving ActiveRecord::ConnectionNotEstablished Error in Rails 6 API

Описание: Learn how to fix the `ActiveRecord::ConnectionNotEstablished (No connection pool with 'primary' found.)` error in your Rails 6 API with a simple adjustment in your controller.
---
This video is based on the question https://stackoverflow.com/q/63893998/ asked by the user 'LT_Chen' ( https://stackoverflow.com/u/1456629/ ) and on the answer https://stackoverflow.com/a/63930430/ provided by the user 'LT_Chen' ( https://stackoverflow.com/u/1456629/ ) 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: ActiveRecord::ConnectionNotEstablished (No connection pool with 'primary' found.) when rendering results

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.
---
Resolving ActiveRecord::ConnectionNotEstablished Error in Rails 6 API

In the world of Rails development, particularly when working with APIs, developers occasionally encounter mysterious errors that can be quite frustrating. One such error is the dreaded ActiveRecord::ConnectionNotEstablished (No connection pool with 'primary' found.). In this guide, we will explore what causes this issue and how to resolve it efficiently.

Understanding the Problem

While working on an API using Rails 6.0, you might find that certain models connect to a secondary database. The example provided showcases a typical database.yml setup for both test and development environments. It seems straightforward: you have a primary database and a secondary database, but an error arises when attempting to render results.

Error Context

The error occurs when the controller attempts to render user details retrieved from the Appuser model. Here’s a breakdown of the related code:

The Appuser model is connected to a secondary database through the TrBase class.

When querying the user details, everything seems to work fine, but the render operation throws the error, indicating that Rails is looking for a connection pool associated with the primary database which isn't established.

Solution to the Problem

The good news is that fixing this error is relatively simple! Here’s how to resolve it step-by-step:

Step 1: Adjust the Render Method

To overcome the connection issue, you need to specify an additional option in your render method. Specifically, by adding each_serializer: nil, you inform Rails not to look for a serializer associated with the primary database.

Here’s the modified show method in your controller:

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

Explanation of the Change

By adding each_serializer: nil, you're effectively bypassing Rails’ expectation of finding a serializer in the primary database. This adjustment acknowledges that your endpoint is solely interacting with the :trmain database, ensuring that the rendering process aligns with the current database context.

Summary of the Update

What Changed? You added each_serializer: nil to the render method.

Why This Works? It prevents Rails from searching for a serializer tied to the 'primary' database, thus eliminating the connection error.

Conclusion

Working with multiple databases in a Rails API can introduce complexities, but understanding how to configure your connections properly can alleviate many issues. The ActiveRecord::ConnectionNotEstablished error, particularly when dealing with secondary databases, can be easily rectified by a simple change in your controller's render method.

Next time you encounter this error, remember this straightforward solution, and you’ll be back on track in no time!

If you have any further questions or additional tips on handling multi-database setups in Rails, feel free to share in the comments below!