Common Scenarios

The implementation of dropdown lists in Simple Form leverages the collection feature. Here are the changes that I made in my related model, controller and view


class Stuff < ApplicationRecord
  belongs_to :user, required: false
  has_one :category


  # GET /stuffs/new
  def new
    @stuff =
    @categories = Category.all


<%= f.input :category_id, as: :select, collection: @categories %>

Overriding the default id

There are two common ways of overriding the default css id in Simple Form. The first way is just to assign it to an id

<%= f.input :category_name, id: 'category_name' %>

The other way is to override it with input_html

<%= f.input :bunch, collection: @bunches, input_html: { id: 'my_bunches_dropdown'} %>

Collection of checkboxes

Let's say you have a model of Posts that has a "has many" relationship with a model of comments and you wanted to create a form with checkboxes associated with those comments. Here's how you'd set it up

<%= simple_form_for(@post) do |f| %>

  <table class="table">
  <%= f.collection_check_boxes :commentss_list, @post.comments, :id, :name do |builder| %>
      <td><%= builder.check_box %></td>
      <td><%= builder.label %></td>
  <% end %>
<% end %>

You can also customize the id of the checkboxes by doing the following:

<td><%= builder.check_box id: "comment_#{}_checkbox" %></td>

Nested models inside of a form

Nested Models let you build forms that update an object and its associated objects all in one shot.

Models are setup the following way

class Person < ApplicationRecord
  has_many :person_contracts
  has_many :contracts, through: :person_contracts

class PersonContract < ApplicationRecord
  belongs_to :person
  belongs_to :contract
  accepts_nested_attributes_for :contract

class Contract < ApplicationRecord
  has_many :person_contracts

Controllers are setup the following way

def new
  @person_contract =

View is setup this way

<%= simple_form_for(@person_contract) do |f| %>
<%= f.error_notification %>
<%= f.error_notification message: f.object.errors[:base].to_sentence if f.object.errors[:base].present? %>

<%= f.input :name %> <%= f.input :description %>

Contract Information

<%= f.simple_fields_for :contracts do |contract_form| %> <%= f.input :contract_value %> <% end %>

<%= f.button :submit, action_name, id: "#{proper_selector_name(action_name, 'id')}_button", class: 'btn btn-primary' %>

<% end %>

Simple Form