Why a Rails form validation error renders the wrong URL and how to fix it
Last updated on December 20, 2021
Before I encountered the following problem, I didn't pay attention to render and redirect_to. I just assumed how they work and let Rails do its magic. But even though correct, the Rails magic confused me whenever I encountered this "bug". I decided to write a short article addressing the simple "cheat" I used.
The following problem is very obscure, but here it comes.
I have used edit/update actions for the following example, but you can apply the same technique to your exact situation.
For the sake of this article, I have a normal User controller with a show, edit and update actions.
1class UserController < ApplicationController2def show3@user = User.first # for testing purposes4end56def edit7@user = User.first # for testing purposes8end910def update11@user = User.first # for testing purposes1213if @user.update user_params14flash[:notice] = 'Details updated.'15redirect_to action: :show16else17flash[:notice] = 'Wrong details. Try again'18render :edit19end20end2122private23def user_params24params.require(:user).permit(:name, :email)25end26end
Routes.rb defines the user resource for these actions
1resources :user, only: [:show, :edit, :update]
which creates the following routes
1Prefix Verb URI Controller#Action2edit_user GET /user/:id/edit(.:format) user#edit3user GET /user/:id(.:format) user#show4PATCH /user/:id(.:format) user#update5PUT /user/:id(.:format)
Important! Notice that the paths for the show and update are the same, but the method verbs are different.
The purpose of the update action is to redirect to the show action if the update has been successful or render the edit form with the validation errors.
In order to test if it works, I go to /user/1/edit and I enter the false information so that the user update fails.
As intended, the form is rendered with the error information. But the new URL is /user/1.
The problem I had is that I refresh the page, I go to the show action - I don't stay in the edit action.
Whenever you press the Submit button of your form, you are being redirected to /user/1 with a PUT verb, which routes to the update action as instructed by our routes.rb file.
If the update action fails the validation, it renders the edit form again - it does not redirect!
Therefore, the URL remains unchanged -/user/1.
At first, we might think that we can change the render to redirect_to - but then we won't get the validation error. So this is not an option.
I decided to update the routes to the following
1resources :user, only: [:show, :edit]2put '/user/:id/edit', to: 'user#update', as: 'update_user'
This maps the PUT http method to /user/:id/edit, so even if the validation fails, I still redirect to the edit action.
If the user refreshes the page, it doesn't matter - the URL still is /user/:id/edit.
The URL of the form needs to be updated to the new URL. In this example, we need to change the form from
1<%= form_for @user, url: user_path(@user), method: :put do |f| %>
1<%= form_for @user, url: update_user_path(@user), method: :put do |f| %>
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