Active Storage & Form Errors: Preventing Lost File Uploads in Rails · Daniela Baron

Rails' Active Storage is a powerful, built-in solution for handling file uploads, providing integration with cloud storage and automatic attachment management. It works out of the box, making it easy to associate files with models. However, when a form includes an attachment and a validation errors occur, the uploaded file is lost when the form re-renders to display the validation errors, forcing users to select their file again. This happens because Active Storage only associates a file with a model after a successful save. If the model fails validation, the attachment is not persisted, and the file selection is lost. This post will walk through a solution using direct uploads, hidden signed IDs, and a custom file input with Stimulus. By the end, you'll have a robust way to ensure users don't lose their file uploads due to form validation errors. The complete working solution is also available on GitHub.