HTML Form Input

Start from basic docs for html input and forms The most important attribute is

  • name identify the input in data submitted with the form. If not provided, this input will not we included.
  • type to identify a input type that input element represents
  • value when specified, it is initial value. For unselected checkbox or radio it is not submitted. They have default value on

There is a lot of input types (like color which will popup color picker) but here we will focus on:

  • text single line text field (line breaks are automatically removed). In rails f.text_field :name, size: 2 or f.number_field :num, min: 1, max: 9 to use shorter width, f.time_field :t will generate type='time' but f.time_select :t will generate select options instead
  • checkbox allowing single value to be selected/deselected. f.check_box :name will submit '0' in case it is not selected, but check_box_tag :name will not.
  • hidden it is not displayed, but value is submitted
  • radio allowing a single value to be selected out of multiple choices, f.radio_button :overnight_rate, 1, label: 'Yes', inline: true, checked: f.object.overnight_rate
  • submit ie <input type='submit' acts like a button that submits the form. You can use <button>OK</button> (default is type='submit') instead (button that does not submit the form is <button type='button'>.

Now start with what Rails provides

Similar to nested forms, you can have select tag with multiple options (habtm relation) so we can update without ajax (it is created in one request). Since in html forms we can only send value or array

  • single value (html name='name') In rails text_field_tag :name and we got params[:name] # => 'Duke'
  • array (html name='ids[]') In rails text_field_tag 'ids[]' or f.text_field :ids, name: 'ids[]' and we got params[:ids] #=> [1,2] Note that you need to permit array params.permit(ids: []). When you remove all elements from DOM than nothing is send to server, so you need to add empty and reject empty values
    before_save :clear_unchecked_values
    def clear_unchecked_values
      self.custom_sign_up_labels = custom_sign_up_labels.reject(&:blank?)
  • hash is when you nest inside brackets and define specific key, for example name='user[name], in rails f.text_field :name (when f.object.class == User). Note that you need to permit each key.

    Hash values can also be string, array or another hash. For array (html name='user[ids][]) in rails you can use f.text_field :ids, name: 'user[ids][] (f.text_field :ids does not make sense since there are multiple input fields, so better is to use text_field_tag :name, but if you are using strong params, than you need to put inside model name, for example "#{}[ids][]") we got params[:user][:ids] #=> [1,2]. Hash with hash values rails use it for fields_for & accepts_nested_attributes_for html name='user[posts_attributes][0][id] and we got params[:user][:posts_attributes]["0"][:id]. Note that you need to permit each key params.require(:user).permit(posts_attributes: [:id,:name])

So for habtm or has_many through, we need to mark for destruction and than add params

# modal
class Book < ApplicationRecord
  has_many :book_topics
  has_many :topics, through: :book_topics
  accepts_nested_attributes_for :book_topics
class BookTopic < ApplicationRecord
  belongs_to :book
  belongs_to :topic

# html
      <%= :topic_ids, options_from_collection_for_select(Topic.all, :id, :topic_name, -> (topic) { topic }), {}, multiple: true %>

# controller
    @book.book_topics.each &:mark_for_destruction
    book_topics_params = {
      book_topics_attributes: params[:book][:topic_ids].map {|id| { topic_id: id } }
    if @book.update _book_params.merge book_topics_params

Nested forms If you want to use nested forms like question and answers, good approach is to create! on new action and redirect to edit. That way you have question_id. For new questions or delete questions, you can simply use ajax. So start with rails g scaffold questions title;rails g model answers question:references.

# models/question.rb
class Question < ActiveRecord::Base
  has_many :answers, dependent: :destroy
  accepts_nested_attributes_for :answers, allow_destroy: true

# questions/_form.html.erb
  <div id="answers">
    <% @question.answers.each do |answer| %>
      <%= render partial: 'answer', locals: { question_form: f, answer: answer } %>
    <% end %>
  <%= link_to "Create new answers", create_answer_question_path, remote: true,
  method: :post %>

# questions/_answer.html.erb
  question_form - we need this because we don't want to generate <form> tags
                - we need just fields
  answer - target answer

  we hard code "answers_attributes[]" because
  when we use fields_for :answer, than when we use ajax `new` twice we got same
  name for different records
  question[answers_attributes][0][id] (value 111)
  question[answers_attributes][0][id] (value 222)
  and only latest will be considered
  it is because uniq number is reset for each fields_for
  this sequential "0", "1" is used so you can show `fields_for :answers` for
  existing and new answers (which does not have id) so they are all separated
  with hard coded `answers_attributes[]` it is
  question[answers_attributes][111][id] (value 111)
  question[answers_attributes][222][id] (value 222)
  but for unsaved objects it will be
  question[answers_attributes][][id] (value nil)
  so there are two solutions:
    * always create objects and than render form
    * add fake id (used for key), but not provide a hidden input field 'id'
<%= question_form.fields_for "answers_attributes[]", answer do |ff| %>
  <div class="field">
    <%= ff.hidden_field :id %>
    <%= ff.text_field :content, placeholder: "Answer" %>
    <%= ff.number_field :score, placeholder: 'Score' %>
    <%= ff.number_field :position, placeholder: 'Position' %>
    <%= link_to "Destroy", destroy_answer_question_path(answer.question, answer_id:, remote: true, method: :delete %>
<% end %>

# questions/create_answer.js.erb
<% output = nil %>
<% form_for(@question) do |f| %>
  <% output = j render partial: 'answer', locals: { question_form: f, answer:
  @answer } %>
  <% end %>
$('#answers').append('<%= output %>');

# config/routes.rb
  resources :questions do
    member do
      post :create_answer
      delete :destroy_answer

# controllers/questions_controller.js
  def create_answer
    @answer = @question.answers.create!

  def destroy_answer
    @answer = @question.answers.find(params[:answer_id])

    def question_params
        :title, :time_limit,
        answers_attributes: [:id, :score, :content, :_destroy]

You can try cocoon gem and use link_to_add_association tutorial post

has_many :ip_addresses, inverse_of: :subscriber is needed when you have validation errors for accepts_nested_attributes_for Validation of uniqueness does not work for bulk update with _attributes since it check only what is in db (not in params), so one solution is to add inverse_of and to add validation

  # this works when we create one record (not for batch update with
  # ip_address_attributes)
  validates :fix_ip_address, presence: true, uniqueness: { scope: :parent_location_id }
  # so we need to validate that also
  validate :uniqueness_for_batch_update
  def uniqueness_for_batch_update
    ips =
    errors.add(:fix_ip_address, 'already exists') if ips.size != ips.uniq.size

Note that callback in nested model, like

class Answer
  before_save :check_something_on_answer

will not be called when answers are updated as answers_attributes

Multiple form submit buttons for different actions

you can use rails builder to show two buttons

  <%= f.submit "Some label" %>
  <%= f.submit "Some other label" %>

will generate

  <input type="submit" name="commit" value="Some label">
  <input type="submit" name="commit" value="Some other label">

so you can check on server

  if params[:commit] == "Some label"

When you are not using f.submit but plain <button>Some label</button> than you need to add hidden_field_tag :commit, "Some label"

Sometimes there is a problem when automatic translator on the page change button labels and inputs so commit param is different… There are two solutions for that: Instead of commit you can use formaction So you do not need to parse commits but you need different action methods to handle.

  <%= form_for('url') do |f| %>
      <%= f.submit 'Create' %>
      <%= f.submit 'Special Action', formaction: special_action_path %>
  <% end %>

Another solution to translations I18 of input submit is to use buttons with value as the same as the text inside button tag.

  <%= form_for('url') do |f| %>
    <%# instead of <input> we use <button> with value (which could be the same as inner text) so automatic page translators do not change that value %>
    <%= f.button 'Create', value: 'Create' %>
    <%= f.button 'Special Action', value: 'Special Action' %>
  <% end %>

this will generate

  <form action="url">
    <button name="button" type="submit" value="Create">Create</button>
    <button name="button" type="submit" value="Special Action">Special Action</button>

so you can grab params[:button] == 'Create'

If you want to disable utf-8 and authenticity hidden fields, remove hidden input name='commit' for submit buttons button_tag 'OK', name: nil and use plain param name instead of in brackets f.hidden_field :name generate name='[name]' (but f.text_field :name generate name='name'), than use hidden_field_tag :name

    <%= bootstrap_form_tag url: @atom_payment.atom_server_link, layout: :horizontal, enforce_utf8: false, authenticity_token: false do |f| %>
      <% @atom_payment.atom_params.each do |atom_param| %>
        <%= hidden_field_tag atom_param[:name], atom_param[:value] %>
      <% end %>
      <%= button_tag "Pay Now", name: nil, class: 'btn btn-primary btn-block', 'data-disable-with': 'Processing...' %>
    <% end %>
  • if you want to access hash keys by symbol or string you can instantiate with params = name: 'Duke' so you can use params[:name] or params["name"].

Here is a rails app, and here is a gist

Rails and Forms

Input outside of a form

<input> can be outside of a <form>, all it needs is form='id_of_a_form'

Dialog element

There is native html tag for modals <dialog>. When you call dialogEl.showModal() there will be backgrop and autofocus is triggered (if there is autofocus attribute).

Fieldset & Legend

Use <fieldset> to group several input fields into one section and set caption label on this part with <legend>.

    My section
  My content

When it is disabled, all nested input fields can not be used, as they were disabled. In Rails 6 I submitted a bug when using remote: true, all nested input fields are submitted so in this case you need to disable manually each input field. But it is fixed now

Another problem with f.fields_for :venue is that if model persists, this will add some hidden venue_attributes[:id] = id

You can set caption also on figure

  <img src="/wp-content/uploads/flamingo.jpg" alt="flamingo">
  <figcaption><i>fig. 1</i> A pink flamingo.</figcaption>

Input Attributes


Pure html autoselect suggestions (but not required from list) can be done using datalist and <input list='id_of_datalist'> attribute.


Autocomplete can be enabled with specific value or disabled because off security (even disabled, browser can ask for auto save password, it will populate them)

Firefox has soft refresh which persist input values and disabled attribute on refresh the page This can be disabled by hard refresh or autocomplete off

But it is advisable to enable autocomplete so user get suggestions on phone

<input id="user-text-field" type="email" autocomplete="username"/>
<input id="password-text-field" type="password" autocomplete="current-password"/>

<%= f.text_field :login, autofocus: true, autocomplete: "email", placeholder: 'Enter Mobile No. / Email ID', skip_label: true, autocapitalize: "off" %>
<%= form.label :mobile, 'What is your Mobile?', class: 'labeltext', autocomplete: "tel" %>
<%= form.text_field :otp_attempt, class: 'form-control', placeholder: 'Enter OTP', autofocus: true, required: true, autocomplete: "one-time-code" %>
<%= :year, options_for_select(year_options, selected: form.object.year), {}, class: 'form-control', id: :year, autocomplete: "bday-year" %>
<%= form.text_field :zip, class: 'form-control', placeholder: 'Enter Your Zipcode', autofocus: true, required: true, autocomplete: "postal-code" %>
<%= form.password_field :password, class: 'form-control', placeholder: "Enter Password (min #{User.password_length.min} chars)", autocomplete: "new-password" %>
<%= form.password_field :password_confirmation, class: 'form-control', placeholder: 'Confirm Password', autocomplete: "new-password" %>


Auto focus input fields on page load (or dialog show). If you need to show focus on input with existing value than you can use callback onfocus

  <%= f.search_field :s, autofocus: true, onfocus: 'this.selectionStart = this.selectionEnd = this.value.length;' %>

or another solution

<%= form.text_field :mobile, class: 'form-control', placeholder: 'Enter Mobile', value: || '+1', autofocus: true, onfocus: 'var temp = this.value; this.value = ""; this.value = temp' %>


Disabled inputs do not receive click event, and they are not submitted with the form. This can be used to preventDefault on click event for other data- event listeners.


required is boolean attribute, when is present, user myst specify a value. On all except (color, hidden, range, submit, image, reset, button). When it is on checkbox than user have to select it before procceeding. Required inputs has pseudoclass :required.


tabindex should be 0 so it is reachable by sequential keyboard navigation.


There are three ways of providing more info about form field, but the best way is using label and to avoid placeholders.

  • label element is outside of a input
  • placeholder text that is shown when field is empty. So when is not empty, no show. Also browsers translators does not work on placeholders since it is attribute (not a value or a text object).
  • adjacent elements (google sign in use this)


form select can accept as 2th param (choices) two variant:

  • flat collection [['name', 123],...]
  • if you need manual tags <select><option></option></select> than you can use <%= select tag "statuses[]", options_for_select([[]], selected: 1) %>
  • nested collection grouped_options_for_select() (also exists f.grouped_collection_select)

    Preselected value can be defined as second param in options_for_select([], selected: f.object.user_id, or as 4th param in options_from_collection_for_select(User.all, :id, :email, selected: f.object.user_id). Note that it can be value or hash selected: value.

as 3th param (options):

Sometimes when options do not include value that you want to set and you use prompt to be shown, please preform check { prompt: 'Select package' }.merge( options.present? ? { selected: } : {} ). If target selected value is not in options, that first option will be used, or prompt is shown when options is empty.

  • disabled: [values] to disable some options
  • label: 'My label'
  • prompt: 'Please select' this is shown only if not already have some value
  • include_blank: 'Please select' this is shown always (even already have value) I found usefull only with select2 where we use custom placeholder and blank option is not selectable <%= :customer_name_and_username, options_from_collection_for_select(current_location.customers, 'id', 'name_and_username'), { include_blank: true, label: 'Customer' }, 'data-select2': true, placeholder: 'Search by Customer Name or Username' %>

as 4th params (html options)

  • multiple: true so it is multi_select (instead of dropdown). Multi select will be shown with its own scrollbar (use size: 5 to limit the size). In controller you need to allow arrays

    def event_params
        :title, skills: []
  • Form array can be set on any input, use square brackets name='user_ids[]'. In view you can set array of hidden fields

     <% @isp_push_packages.isp_package_ids.each do |isp_package_id| %>
       <%= f.hidden_field 'isp_package_ids[]', value: isp_package_id %>
     <% end %>

    or using select multiple: true (it will automatically add [] to the name)

      <%= isp_package_ids, options, {}, multiple: true %>

    Note that you can replace dropdown select input with checkboxes, for example

      <% ApplicationRecord.split_and_convert_to_hash(LANGUAGES).values.each do |language| %>
     <%= f.check_box 'languages_spoken_at_home', { multiple: true, label: language}, language, nil %>
      <% end %>

You can also nest in two dimensions ie it will be a hash with array values name='user_ids[#{}][]. In this case you need to permit hash (Rails 5.2) or whitelist in before Rails 5.2

  params.require(:post).permit(reseller_location_ids: {}) # Rails 5.2
  permit(files: params[:post][:files].key # before Rails 5.2

  <%= select_tag 'reseller_location_ids[#{}]', options, multiple: true %>
  # do not know how to use since can not have method with a name

Note that if it is not required and nothing is selected than nothing will be sent, you should use hidden field or default value {}

  <%= hidden_field_tag 'reseller_location_ids[0][]' %>
  # or
  location_ids = (params[:reseller_location_ids] || {})[params[:reseller_operator_id]] || []
  • And in model you need to clean empty strings [""] when nothing is selected
      before_validation :clean_empty_skills
      def clean_empty_skills
     self.skills = &:present?

examples TODO

instead of polymorhic, we could use separate columns isp_id, operator_id, location_id. it is hard to search by that colum

for specific form inputs to ask, you can use fieldset and disable those which are not necessary.

Single line oneliner form in one line is using button_to with params: label, url, form class

<%= button_to 'Email bounce', superadmin_user_path(@user, user: { email_bounce: true }), method: :patch, class: 'btn btn-danger', form_class: 'd-inline' %>

<%= link_to "Fair usage policy", expire_subscriber_path(@subscriber, button: 'fair_usage_policy'), method: :patch, class: 'btn btn-primary' %>

Default is using POST, but you can change and add params

  • in rails <%= form_with ..., class: 'my-class' you can use class attribute directly, but other attributes are not passed, so you need to use html like <%= form_with ..., html: { class: 'my-class' } %>
  • optional permit params that allows empty
    def _my_form_params
      params[:my_from] = {name: ""} unless params.keys.include? "my_from"