This article was originally posted on my blog.
Sometimes an array of data needs to be submitted in an HTML form. A form to send invites to a bunch of users for example. That'd just be a series of email fields; and in the controller; we'd want an array of the emails to iterate over and send invites.
Rails form helpers are set up to have a key and value for each field, so it's not immediately obvious how to send an array of data. But in Rails, there's always a way!
If we append
 to the
name of a field, it'll be parsed as an array! So for an array of emails to send invites; setting
invites on all the email fields and gives us an array in the controller.
To generate the form, we can use the following code:
<%= form_with(scope: :invites, url: invite_path) do |form| %> <% 3.times do %> <!-- id has to be nil to prevent clashes as all fields would have the same id --> <%= form.email_field nil, id: nil, placeholder: "Email Address" %> <% end %> <%= form.submit %> <% end %>
nil as the first argument to
email_field instead of a name gives us the
 we need for an array. The generated markup looks like:
<form action="/invite" accept-charset="UTF-8" data-remote="true" method="post"> <input type="hidden" name="authenticity_token" value="...."> <input placeholder="Email Address" type="email" name="invites"> <input placeholder="Email Address" type="email" name="invites"> <input placeholder="Email Address" type="email" name="invites"> <input type="submit" name="commit" value="Save Invites" data-disable-with="Save Invites"> </form>
On the controller, we can use the submitted data as:
def create invited_users = params.require(:invites) p invited_users # => ["firstname.lastname@example.org", "email@example.com", "firstname.lastname@example.org"] end
To permit an array parameter in a nested form field, we can use the following pattern:
It's a little unintuitive but submitting arrays from a form can be a useful tool in your toolbox!