Error messages and display in Ruby on Rails

Introduction

Error messages help users know what went wrong when they fill out forms or use your app. Showing these messages clearly makes your app easier and friendlier to use.

When a user submits a form with missing or wrong information

When saving data fails because of validation rules

When you want to guide users to fix mistakes in their input

When you want to show success or failure feedback after an action

When debugging or logging errors during development

Syntax

Ruby on Rails

if @model.errors.any?
  @model.errors.full_messages.each do |message|
    # display message
  end
end

@model.errors.any? checks if there are any errors on the model.

@model.errors.full_messages gives a list of readable error messages.

Examples

This example shows how to display all error messages for a user in a list inside a view.

Ruby on Rails

<% if @user.errors.any? %>
  <div class="error-messages">
    <h2><%= pluralize(@user.errors.count, "error") %> prevented this user from saving:</h2>
    <ul>
      <% @user.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
    </ul>
  </div>
<% end %>

This example shows how to display an error message next to a specific form field (using a helper method).

Ruby on Rails

<%= form_with model: @post do |form| %>
  <%= form.label :title %>
  <%= form.text_field :title %>
  <%= form.error_message_on :title %>
  <%= form.submit %>
<% end %>

Sample Program

This example shows a simple Rails form for creating a user. If the user submits invalid data, error messages appear above the form. The form fields have ARIA attributes for accessibility.

Ruby on Rails

# app/controllers/users_controller.rb
class UsersController < ApplicationController
  def new
    @user = User.new
  end

  def create
    @user = User.new(user_params)
    if @user.save
      redirect_to root_path, notice: "User created successfully"
    else
      render :new
    end
  end

  private

  def user_params
    params.require(:user).permit(:name, :email)
  end
end

# app/views/users/new.html.erb
<h1>New User</h1>
<% if @user.errors.any? %>
  <div aria-live="polite" role="alert" class="error-messages">
    <h2><%= pluralize(@user.errors.count, "error") %> prevented this user from saving:</h2>
    <ul>
      <% @user.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
    </ul>
  </div>
<% end %>

<%= form_with model: @user do |form| %>
  <div>
    <%= form.label :name %><br>
    <%= form.text_field :name, aria: { describedby: 'name_error' } %>
  </div>
  <div>
    <%= form.label :email %><br>
    <%= form.email_field :email, aria: { describedby: 'email_error' } %>
  </div>
  <div>
    <%= form.submit "Create User" %>
  </div>
<% end %>

Important Notes

Always use aria-live="polite" and role="alert" on error message containers for screen readers.

Use pluralize helper to show correct singular/plural wording.

Place error messages near the related form fields for better user guidance.

Summary

Error messages tell users what went wrong and how to fix it.

Use @model.errors.full_messages to get readable messages.

Show errors clearly and accessibly in your views.