How to Resolve undefined method asset_url in Ruby on Rails
Ruby on Rails is a great framework for quickly spinning up and managing back-end or full-stack applications. Its motto, “Convention over Configuration,” ensures that if you use the built-in objects and methods as intended, you will get consistent and reliable results. Sometimes you may need to break convention to get the functionality you desire. To do this you must understand what the Rails built-in helpers do and if you have to explicitly include them in the model, class, view, or helper you are working in. This is an issue I had to address when trying to use asset_path and asset_url in a Controller.
What are the asset_path and asset_url Methods?
The asset_path and asset_url methods are both methods defined in ActionView::Helpers::AssetUrlHelper. They allow users to create relative paths to an asset in the public directory (asset_path) or full URLs for an asset in the public directory (asset_url).
These methods are useful as they dynamically create the links to the specific asset, making your code more concise and less brittle. They are intended to be used in ERB files, as those are the files that work with ActionView objects. However, if you know how to rework Rails’ method use conventions, you can use them outside of ActionView modules.
How to Solve Undefined Method Errors for asset_path and asset_url
Now that we know the difference between asset_url and asset_path, we can address how to use them outside their conventional bounds. As we discussed above, both of these methods are part of the ActionView object. This means that they are not implicitly understood by the controller, model, or helper modules. If we want to solve an error like `undefined method `asset_url` for #<DirName::MyController:0x00008ghd9sh70>` we must tell Rails where to look for the method.
In my case, I was trying to call asset_url inside a helper module called by a controller. Because the method is not inherited by ActionController, I had to explicitly include it by adding the line of code `include ActionView::Helpers::AssetUrlHelper` at the top of my Helper file. Once I made this change, Rails found the asset_url method, fixing my code.
