SimpleForm: forms made easy

Sometime ago we were working on a project together with a designer, and that specific application was full of forms, each one having a different layout, but most of them sharing the same features: inline errors, hints, specific label markup for required fields, etc. To start prototyping the application faster, we used the markup the designer created with similar forms, duplicating the code. But we don’t like code duplication, we weren’t feeling comfortable with it. So we decided to move on and create a tool to help us, that should be flexible enough to let us define the markup that fits better for each application, or even no extra markup at all. Here is SimpleForm!

SimpleForm inputs

From the README:

Forms made easy (for Rails)!

SimpleForm aims to be as flexible as possible while helping you with powerful components to create your forms. The basic goal of simple form is to not touch your way of defining the layout, letting you find the better design for your eyes. Good part of the DSL was inherited from Formtastic, which we are thankful for and should make you feel right at home.

As the README says, SimpleForm is a tool to help you build forms easily in Rails. Let’s see some examples:

<%= simple_form_for @user do |f| %>
  <%= f.input :username, :label => 'Your username please' %>
  <%= f.input :password, :hint => 'No special characters.' %>
  <%= f.input :remember_me, :as => :boolean %>
  <%= f.button :submit %>
<% end -%>

There are plenty of things going on here: we create a form using simple_form_for helper, then we use the :input method to create input elements based on column type. For instance, :username will create a default text input, while :password attribute will render an input type password. For the :username attribute, we are specifying a label manually. For :password, the label will be taken from I18n, and we are adding a hint message to the field. For :remember_me, we are explicitly saying to render it as a checkbox, using the :as => :boolean option (that is the default for boolean attributes). Also, there is a button helper that simply delegates to Rails helpers, in this case submit.

The output for a new @user would be:

No special characters.

You may have noticed there is some additional css classes added to the markup, like string and required. They are added automatically by SimpleForm to help us style and plug some javascript in. There are specific css classes for each available input type. Also, pay some attention to the label: inside it there is an abbr tag with an asterisk (*) showing that the field is required. SimpleForm uses the new validations reflection API from Rails 3 to check if the attribute has the presence validator, and mark the field as required if so. And we are able to say that a field is required or disable the required mark, by passing the option :required => true|false.

Furthermore, there is the hint tag for the :password attribute that SimpleForm creates based on the :hint option we have defined. Also notice that the gem has automatically added a div wrapper to each input, with the same css classes. SimpleForm allows us to configure this wrapper as well, using for instance p instead of div. We are going to see more about configuration later.

SimpleForm is already prepared to generate some of the new HTML 5 input tags, such as email, url and number inputs:

<%= simple_form_for @user do |f| %>
  <%= f.input :website, :as => :url %>
  <%= f.input :email %>
  <%= f.input :age, :hint => "This defaults to 'number' input based on field type" %>
  <%= f.button :submit %>
<% end -%>

Based on the attribute name, SimpleForm will generate url or email input types, and we can always set a specific type with the :as option. Numeric attributes will always be rendered as input type number.

Working with associations

SimpleForm adds a custom and straightforward method to render select tags for associations, called association. For now, consider our User belongs to a Company, and has and belongs to many Roles. Let’s go straight to the example:

<%= simple_form_for @user do |f| %>
  <%= f.input :name %>
  <%= f.association :company %>
  <%= f.association :roles %>
  <%= f.button :submit %>
<% end -%>

It will detect the association type and render a select tag for choosing the company, listing all companies in the database, and another select for roles, with multiple option enabled.

SimpleForm also has some add-ons, letting us render associations as a collection of radios or check boxes. Using the same example:

  f.association :company, :as => :radio
  f.association :roles, :as => :check_boxes

Now we are rendering a collection of radios for choosing the Company, and another collection of check boxes for choosing Roles.

Configuration

SimpleForm lets us do some customizations by running its install generator:

rails generate simple_form:install

# Output
  create  config/initializers/simple_form.rb
  create  config/locales/simple_form.en.yml
  create  lib/templates/erb/scaffold/_form.html.erb

As we can see, running this generator will copy an initializer file, responsible for configuring SimpleForm; a locale file, to let us change some I18n messages; and a form template inside our lib dir. This template will be used instead of the default Rails scaffold form template, so it will create our form already using SimpleForm. Easy, right?

Let’s take a look at some configuration options:

  • components: defines the components used by the form builder. We can remove any of them, change the order, or add new ones. Defaults to [ :label, :input, :hint, :error ].
  • hint_tag: tag used for hints, defaults to span.
  • error_tag: tag used for errors, defaults to span.
  • wrapper_tag: tag used as wrapper to all inputs, defaults to div
  • label_text: determines how the label text should be generated altogether with the required text. It must be a lambda/proc that receives both label and required texts. Defaults to "required label".

There are a lot more options available in the initializer file, such as default input size and priority countries for generating country selects. Also, the locale file lets us determine the required text and mark, or even the entire required html tag.

Internationalization

SimpleForm is ready for I18n, supporting labels and hints. In addition, it lets us set different content for each action, new and edit. Here is an example locale file:

  en:
    simple_form:
      labels:
        user:
          username: 'User name'
          password: 'Password'
          edit:
            username: 'Change user name'
            password: 'Change password'
      hints:
        user:
          username: 'User name to sign in.'
          password: 'No special characters, please.'

Simple, right? If it does not find any specific translation using I18n for the label, it will fallback to human_attribute_name.

Here we go!

SimpleForm has much more to offer. We would like to invite you to take a better look at the examples and possibilities. Remember, SimpleForm aims to be flexible and powerful to help you easily build forms, without saying how you should create your markup.

Also, feel free to explore the source code and extend SimpleForm even further. Since it’s based on components, creating a new component which moves the current hints to inside the input (using javascript or the new placehoder attribute in HTML 5), should be easy!

It’s worth saying SimpleForm is Rails 3 compatible in the master branch. If you are using Rails 2.3.x, there is a v1.0 branch and version that you might want to take a look.

SimpleForm has been helping us a lot so far, we hope you enjoy it. Moreover, we would like to enjoy other tools that help your productivity day by day, please leave a comment and let us know, we would appreciate a lot!

  • adam

    ok..nice… but why use this instead of formtastic?

  • adam

    ok..nice… but why use this instead of formtastic?

  • Gavin

    Great work guys! I’m using this on project already and love it.

  • Gavin

    Great work guys! I’m using this on project already and love it.

  • José Valim

    @adam, one of the most important features in Formtastic is that it’s quite opinionated about your markup. Sometimes, we get the design straight from our client and we are not supposed to redesign the form markup, meaning we cannot use Formtastic (as said in the beginning of the text). So, if you need a more flexible solution, not opinionated on markup, I recommend you to use SimpleForm. But, if you are free to choose your markup and love Formtastic one, stick with it!

  • José Valim

    @adam, one of the most important features in Formtastic is that it’s quite opinionated about your markup. Sometimes, we get the design straight from our client and we are not supposed to redesign the form markup, meaning we cannot use Formtastic (as said in the beginning of the text). So, if you need a more flexible solution, not opinionated on markup, I recommend you to use SimpleForm. But, if you are free to choose your markup and love Formtastic one, stick with it!

  • http://raphaelcosta.net Raphael Costa

    Nice Plugin… good bye formtastic…

  • http://raphaelcosta.net Raphael Costa

    Nice Plugin… good bye formtastic…

  • http://xilinus.com seb

    @adam, I switched from Formtastic to SImpleForm for the markup reason that José said. But also because you can extend easily SimpleForm, it was rails 3 compatible a long time ago and I prefer the code. Reading the code is always a good thing to do before using a gem/plugin.

    Opinionated response of course :)

  • http://xilinus.com seb

    @adam, I switched from Formtastic to SImpleForm for the markup reason that José said. But also because you can extend easily SimpleForm, it was rails 3 compatible a long time ago and I prefer the code. Reading the code is always a good thing to do before using a gem/plugin.

    Opinionated response of course :)

  • http://www.bitcetera.com/en/techblog Svoop

    Nice work! If you want to make it distinct from Formtastic though, I suggest you integrate show_form_for so the same partial could be used for both show and edit actions. Two obvious places to add it to the DSL would be either “” or “”, but I’m sure you’d come up with a better solution.

  • http://www.bitcetera.com/en/techblog Svoop

    Nice work! If you want to make it distinct from Formtastic though, I suggest you integrate show_form_for so the same partial could be used for both show and edit actions. Two obvious places to add it to the DSL would be either “” or “”, but I’m sure you’d come up with a better solution.

  • http://www.bitcetera.com/en/techblog Svoop

    Oops, the ERB got stripped, here’s the content of the empty “” above: “simple_form_for @user, false do |f|” or “f.show true”.

  • http://www.bitcetera.com/en/techblog Svoop

    Oops, the ERB got stripped, here’s the content of the empty “” above: “simple_form_for @user, false do |f|” or “f.show true”.

  • http://carlosantoniodasilva.wordpress.com Carlos Antonio

    @svoop if I remember this was already requested, but is not an easy deal. Actually I’m not sure how good it’d be, to put SimpleForm and ShowFor talking together, mostly because they have different options in the majority of their components.
    If we integrate both libs, chances are people will need some sort of configuration to setup a specific option just for ShowFor or SimpleForm in that specific case, and it might turn them a bit harder to maintain.
    Anyway, I haven’t tried that but if you have a small forms that are just :inputs or :associations, without any specific option, you could easily separate into a partial, as SimpleForm uses :attribute as an alias for :input, making the DSL pretty similar to ShowFor.

  • http://carlosantoniodasilva.wordpress.com Carlos Antônio

    @svoop if I remember this was already requested, but is not an easy deal. Actually I’m not sure how good it’d be, to put SimpleForm and ShowFor talking together, mostly because they have different options in the majority of their components.
    If we integrate both libs, chances are people will need some sort of configuration to setup a specific option just for ShowFor or SimpleForm in that specific case, and it might turn them a bit harder to maintain.
    Anyway, I haven’t tried that but if you have a small forms that are just :inputs or :associations, without any specific option, you could easily separate into a partial, as SimpleForm uses :attribute as an alias for :input, making the DSL pretty similar to ShowFor.

  • cncardoso

    Great work! Its nice to have flexible markup.

    One question:
    How SimpleForm deals with nested forms and ‘has many’ associations?

  • cncardoso

    Great work! Its nice to have flexible markup.

    One question:
    How SimpleForm deals with nested forms and ‘has many’ associations?

  • Juanma

    Great work guys!

    I wish I had a google group for discussing and learning to use this plugin.
    I have a question, that I have tried to resolve with no luck:
    How can I inject a “” tag after the label as the rails scaffold do.
    I would like to have the same markup.

  • Juanma

    Great work guys!

    I wish I had a google group for discussing and learning to use this plugin.
    I have a question, that I have tried to resolve with no luck:
    How can I inject a “” tag after the label as the rails scaffold do.
    I would like to have the same markup.

  • Juanma


    How can I inject a “br” tag after the label as the rails scaffold do?

    Sorry, The html tag was stripped in the prior message.

  • Juanma


    How can I inject a “br” tag after the label as the rails scaffold do?

    Sorry, The html tag was stripped in the prior message.

  • José Valim

    Juanma, this is documented in the generated file. Just check this file.

    You just need to give a proc with the behavior you wish. :)

  • José Valim

    Juanma, this is documented in the generated file. Just check this file.

    You just need to give a proc with the behavior you wish. :)

  • Elliot Winkler

    Dudes… this is awesome. I tried Formtastic for a while and really didn’t like it ’cause it was so restricting. This makes a lot more sense. Definitely have to give this a try in my next app.

  • Elliot Winkler

    Dudes… this is awesome. I tried Formtastic for a while and really didn’t like it ’cause it was so restricting. This makes a lot more sense. Definitely have to give this a try in my next app.

  • szimek

    Why do you use inline hints instead of “placeholder” attribute? Formtastic uses the same approach, so I guess there must be some reasoning behind this… :)

  • szimek

    Why do you use inline hints instead of “placeholder” attribute? Formtastic uses the same approach, so I guess there must be some reasoning behind this… :)

  • José Valim

    Szymon, unfortunately not all browsers support placeholder yet, so we would need to depend on Javascript which I think is something we don’t want to do by default. In any case, changing SimpleForm to use placeholder instead of hint in your app should be piece of cake! :)

  • José Valim

    Szymon, unfortunately not all browsers support placeholder yet, so we would need to depend on Javascript which I think is something we don’t want to do by default. In any case, changing SimpleForm to use placeholder instead of hint in your app should be piece of cake! :)

  • cncardoso

    I’m gonna try to use SimpleForm in my next project. How do I declare nested forms to deal with ‘has many’ associations with multiple fields?
    Formtastic uses ‘semantic_fields_for’. Is there a similar option?

  • cncardoso

    I’m gonna try to use SimpleForm in my next project. How do I declare nested forms to deal with ‘has many’ associations with multiple fields?
    Formtastic uses ‘semantic_fields_for’. Is there a similar option?

  • http://carlosantoniodasilva.wordpress.com Carlos Antonio

    @cncardoso yes, you can use simple_fields_for as well.

  • http://carlosantoniodasilva.wordpress.com Carlos Antônio

    @cncardoso yes, you can use simple_fields_for as well.

  • http://www.lightweb.pl mican

    How to translate submit label in simple_form yml?

  • http://www.lightweb.pl mican

    How to translate submit label in simple_form yml?

  • http://carlosantoniodasilva.wordpress.com Carlos Antonio

    @mican if you’re using SimpleForm in a Rails 3 app, the submit button has already been internationalized, so you can take a look there. For Rails 2.3.x apps, you can use the keys :create, :update and :submit under simple_form.buttons.

  • http://carlosantoniodasilva.wordpress.com Carlos Antônio

    @mican if you’re using SimpleForm in a Rails 3 app, the submit button has already been internationalized, so you can take a look there. For Rails 2.3.x apps, you can use the keys :create, :update and :submit under simple_form.buttons.

  • Anonymous

    testando disqus

  • http://blog.plataformatec.com.br/ josevalim

    Juanma, this is documented in the generated file. Just check this file.

    You just need to give a proc with the behavior you wish. :)

  • http://blog.plataformatec.com.br/ josevalim

    Szymon, unfortunately not all browsers support placeholder yet, so we would need to depend on Javascript which I think is something we don't want to do by default. In any case, changing SimpleForm to use placeholder instead of hint in your app should be piece of cake! :)

  • http://blog.plataformatec.com.br/ josevalim

    @adam, one of the most important features in Formtastic is that it's quite opinionated about your markup. Sometimes, we get the design straight from our client and we are not supposed to redesign the form markup, meaning we cannot use Formtastic (as said in the beginning of the text). So, if you need a more flexible solution, not opinionated on markup, I recommend you to use SimpleForm. But, if you are free to choose your markup and love Formtastic one, stick with it!

  • http://welcometonewnepal.com Millisami

    How to use it with Haml?

  • Erik Dahlstrand

    This gem is really a gem! Thank you and keep up the good work :)

  • Anonymous

    ok a newbe question – How do I create the controller for something like a simple website contact form?

  • tspore

    In text_area how do I change cols = “40” -