How to Use form_with in Rails: Syntax and Examples

Use form_with in Rails to create forms by passing a model or URL and options. It automatically handles form submission and generates HTML form tags with proper attributes. Use the block form to add form fields inside the form.

Syntax

The basic syntax of form_with uses a model or URL and a block to define form fields. You can pass options like local: true to disable AJAX submission.

• model: The Active Record object the form is for.
• url: The path where the form submits.
• local: When true, submits with normal HTTP instead of AJAX.
• block: The form fields inside the form.

ruby

form_with(model: @article, local: true) do |form|
  # form fields here
end

Example

This example shows a form for a new Article model with fields for title and body. It uses form_with with local: true to submit normally.

ruby

class ArticlesController < ApplicationController
  def new
    @article = Article.new
  end

  def create
    @article = Article.new(article_params)
    if @article.save
      redirect_to @article
    else
      render :new
    end
  end

  private

  def article_params
    params.require(:article).permit(:title, :body)
  end
end

# In app/views/articles/new.html.erb
<%= form_with(model: @article, local: true) do |form| %>
  <div>
    <%= form.label :title %><br>
    <%= form.text_field :title %>
  </div>
  <div>
    <%= form.label :body %><br>
    <%= form.text_area :body %>
  </div>
  <div>
    <%= form.submit "Create Article" %>
  </div>
<% end %>

Output

<form action="/articles" accept-charset="UTF-8" method="post">
  <div>
    <label for="article_title">Title</label><br>
    <input type="text" name="article[title]" id="article_title">
  </div>
  <div>
    <label for="article_body">Body</label><br>
    <textarea name="article[body]" id="article_body"></textarea>
  </div>
  <div>
    <input type="submit" name="commit" value="Create Article" data-disable-with="Create Article">
  </div>
</form>

Common Pitfalls

Common mistakes when using form_with include:

• Not setting local: true when you want a normal form submit, which causes AJAX submission by default.
• Forgetting to pass a model or URL, which leads to errors.
• Using form_for or form_tag instead of form_with in new Rails versions.

Example of wrong and right usage:

erb

<!-- Wrong: AJAX submit when you want normal submit -->
<%= form_with(model: @article) do |form| %>
  <!-- fields -->
<% end %>

<!-- Right: normal submit -->
<%= form_with(model: @article, local: true) do |form| %>
  <!-- fields -->
<% end %>

Quick Reference

Summary tips for using form_with:

• Use model: for forms tied to Active Record objects.
• Use url: for forms not tied to models.
• Set local: true to disable AJAX if you want normal form submission.
• Use the block parameter to access form helpers like text_field, text_area, and submit.
• Rails 5.1+ prefers form_with over form_for and form_tag.

Key Takeaways

Use form_with with a model or URL and a block to create forms in Rails.

Set local: true to disable AJAX and submit forms normally.

Use form_with helpers inside the block to add input fields and buttons.

Avoid using deprecated form_for or form_tag in new Rails apps.

Always pass either a model or a URL to form_with to avoid errors.