Rails Forms

To me, forms in web applications feel antiquated. There are better ways to get data from a user, such as getting access to a user’s other accounts (like Twitter or Facebook) via OAuth and populating data from there, but that’s not always an option. For now, we still have to input data manually and that means we need to use forms.

Forms are obnoxious. You have to pick out which input types are best for your scenario (text, radio buttons, dropdown lists, etc.). You need to style it with CSS so it looks presentable You need to define a route for the form to submit data to the back end. You have to deal with data validations and handle scenarios where users input unacceptable data. And you have to deal with a host of other miscellaneous issues that come with such complex interaction.

Here’s a sample HTML form:

<form action="users" method="post" accept-charset="UTF-8">
  <fieldset>
    First name:<br>
    <input type="text" name="firstname"><br>
    Last name:<br>
    <input type="text" name="lastname"><br><br>
    <input type="submit" value="Submit">
  </fieldset>
</form>

Fortunately, Rails can help you generate forms using a few different tools which we’ll look at here.

form_tag

form_tag is a Rails form helper used to help you build a basic form.

Here’s a sample form_tag form:

<%= form_tag("/users") do %>
  Name: <%= text_field_tag "name" %><br>
  Email: <%= text_field_tag "email" %>
  <%= submit_tag "Create User" %>
<% end %>

The actual HTML that’s produced will look like this:

<form action="/users" accept-charset="UTF-8" method="post">
 <input name="utf8" type="hidden" value="&#x2713;" />
 <input type="hidden" name="authenticity_token" value="TKTzvQF+atT/XHG/7h48xKVdXvILdiPj83XQhn2mWBNNhvv0Oh5YfAl2LM3DlHsQjbMOFVsYEyOwj+rPaSk3Bw==" />
 Name: <input type="text" name="name" id="name" /><br />
 Email: <input type="text" name="email" id="email" />
 <input type="submit" name="commit" value="Create User" />
</form>

Just with a few simple lines of ERB, we’re able to create a fully realized form. It has an action and method already defined, as well as an authenticity token which is used to help prevent cross-site request forgeries.

However, form_tag is limited, specifically when it comes to dealing with forms directly related to back end models. If you want a different action method (such as wanting to reuse the same form for creating and editing a model), you have to specify it manually. It also won’t populate the form with data that’s already there. That’s where form_for comes in.

form_for

form_for is like form_tag in that it helps you generate a form with ERB tags in a view template. However, form_for directly connects with a model in your Rails application and makes it easy to allow the creation of new model instances in your database.

Here’s a sample form_for form:

<%= form_for @post do |f| %>
 <%= f.text_field :title %>
 <%= f.text_area :content %>
 <%= f.submit %>
<% end %>

This creates the following HTML:

<form class="edit_post" id="edit_post" action="/posts/1" accept-charset="UTF-8" method="post">
 <input name="utf8" type="hidden" value="&#x2713;" />
 <input type="hidden" name="_method" value="patch" />
 <input type="hidden" name="authenticity_token" value="nRPP2OqVKB00/Cr+8EvHfYrb5sAkZRtr8f6dzBaJAI+cMceR0fUatcLWd4zdwYCpojW2J3QLK6uyBKeFAgZvmw==" />
 <input type="text" name="post[title]" id="post_title" value="Existing Post Title"/>
 <textarea name="post[content]" id="post_content">Existing Post Content</textarea>
 <input type="submit" name="commit" value="Update Post" />
</form>

This is something that we can reuse for a create and an edit form, and it will populate data in the form automatically if there’s data there. The thing to remember here is that form_for needs an instance of the model to use which has to be provided from the controller. So for example:

def new
  @post = Post.new
end

Of course now we need to wire these forms up with controllers in the back end to actually process the data, but that’s a topic for another day.

You can read more about Rails forms in the Rails Guides.