Handling Forms and User Input in Rails

1. Introduction

In this tutorial, we are going to explore how to handle user input through forms in a Rails application. We will capture and process form data to perform CRUD operations (Create, Read, Update, Delete).

By the end of this tutorial, you will be able to:

• Understand how forms work in Rails
• Create a form to accept user input
• Validate the data received from a form
• Save the data to a database

Prerequisites:
- Basic understanding of Ruby and Rails
- Rails installed on your machine
- Basic knowledge of HTML

2. Step-by-Step Guide

Rails provide several helpers to work with forms. The most common one is form_with.

form_with

form_with is a form builder provided by Rails. It's a method that accepts a block of code, which describes the contents of the form.

<%= form_with do |form| %>
  ...
<% end %>

Inside the block, you can use other form helpers to create fields. For example, form.text_field creates a text field, form.label creates a label, and form.submit creates a submit button.

<%= form_with do |form| %>
  <%= form.label :name, 'Your Name:' %>
  <%= form.text_field :name %>
  <%= form.submit 'Submit' %>
<% end %>

Form Data Processing

When the form is submitted, the data is sent to the server. In Rails, you typically define a route, a controller, and an action to handle the form data.

# routes.rb
resources :users, only: [:new, :create]

# users_controller.rb
def create
  @user = User.new(user_params)
  if @user.save
    redirect_to @user
  else
    render 'new'
  end
end

private

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

3. Code Examples

Let's create a form for a User model. Our User model has a name and email.

# app/models/user.rb
class User < ApplicationRecord
  validates :name, presence: true
  validates :email, presence: true
end

Now, let's create a new view with a form to create a new user.

# app/views/users/new.html.erb
<%= form_with model: @user do |form| %>
  <%= form.label :name %>
  <%= form.text_field :name %>

  <%= form.label :email %>
  <%= form.text_field :email %>

  <%= form.submit %>
<% end %>

Finally, let's create the new and create actions in UsersController.

# 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 @user
    else
      render 'new'
    end
  end

  private

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

4. Summary

In this tutorial, we learned how to handle forms in Rails. We learned about the form_with helper, how to create different form fields, and how to process form data in a controller.

To further your learning, practice creating forms for different models, and try using different form helpers.

Some useful resources:
- Rails Guide: Form Helpers
- Rails API Documentation: form_with

5. Practice Exercises

1. Create a form for a Product model with name, description, and price fields.
2. Add validation to the Product model. name and price should be required, and price should be a number greater than 0.
3. In the ProductsController, create new and create actions to handle the form data.

For further practice, try creating a form to update an existing record, and an action in the controller to handle the update request.