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Reform

Decouple your models from forms. Reform gives you a form object with validations and nested setup of models. It is completely framework-agnostic and doesn't care about your database.

Although reform can be used in any Ruby framework, it comes with Rails support, works with simple_form and other form gems, allows nesting forms to implement has_one and has_many relationships, can compose a form from multiple objects and gives you coercion.

![](https://raw.githubusercontent.com/apotonick/trailblazer/master/doc/trb.jpg)

Reform is part of the Trailblazer project. Please buy my book to support the development and learn everything about Reform. Currently the book discusses:

  • Form objects, the DSL and basic API (chapter 2 and 3)
  • Basic validations and rendering forms (chapter 3)
  • Nested forms, prepopulating and validation populating and pre-selecting values (chapter 5)

More chapters are coming!

Installation

Add this line to your Gemfile:

gem 'reform'

Nomenclature

Reform comes with two base classes.

  • Form is what made you come here - it gives you a form class to handle all validations, wrap models, allow rendering with Rails form helpers, simplifies saving of models, and more.
  • Contract gives you a sub-set of Form: this class is meant for API validation where already populated models get validated without having to maintain validations in the model classes.

Defining Forms

You're working at a famous record label and your job is archiving all the songs, albums and artists. You start with a form to populate your songs table.

class SongForm < Reform::Form
  property :title
  property :length

  validates :title, presence: true
  validates :length, numericality: true
end

Define your form's fields using ::property. Validations no longer go into the model, but into the form.

Luckily, this can be shortened as follows.

class SongForm < Reform::Form
  property :title, validates: {presence: true}
  property :length, validates: {numericality: true}
end

Use properties to bulk-specify fields.

class SongForm < Reform::Form
  properties :title, :length, validates: {presence: true} # both required!
  validates :length, numericality: true
end

After explicitely defining your fields, you're ready to use the form.

The API

Forms have a ridiculously simple API with only a handful of public methods.

  1. #initialize always requires a model that the form represents.
  2. #validate(params) updates the form's fields with the input data (only the form, not the model) and then runs all validations. The return value is the boolean result of the validations.
  3. #errors returns validation messages in a classy ActiveModel style.
  4. #sync writes form data back to the model. This will only use setter methods on the model(s).
  5. #save (optional) will call #save on the model and nested models. Note that this implies a #sync call.

In addition to the main API, forms expose accessors to the defined properties. This is used for rendering or manual operations.

Setup

In your controller you'd create a form instance and pass in the models you want to work on.

class SongsController
  def new
    @form = SongForm.new(Song.new)
  end

You can also setup the form for editing existing items.

class SongsController
  def edit
    @form = SongForm.new(Song.find(1))
  end

Reform will read property values from the model in setup. Given the following form class.

class SongForm < Reform::Form
  property :title

Internally, this form will call song.title to populate the title field.

If you, for whatever reasons, want to use a different public name, use :from.

class SongForm < Reform::Form
  property :name, from: :title

This will still call song.title but expose the attribute as name.

Rendering Forms

Your @form is now ready to be rendered, either do it yourself or use something like Rails' #form_for, simple_form or formtastic.

= form_for @form do |f|

  = f.input :name
  = f.input :title

Nested forms and collections can be easily rendered with fields_for, etc. Just use Reform as if it would be an ActiveModel instance in the view layer.

Note that you have a mechanism to prepopulate forms for rendering.

Validation

After a form submission, you want to validate the input.

class SongsController
  def create
    @form = SongForm.new(Song.new)

    #=> params: {song: {title: "Rio", length: "366"}}

    if @form.validate(params[:song])

The #validate method first updates the values of the form - the underlying model is still treated as immutuable and remains unchanged. It then runs all validations you provided in the form.

It's the only entry point for updating the form. This is per design, as separating writing and validation doesn't make sense for a form.

This allows rendering the form after validate with the data that has been submitted. However, don't get confused, the model's values are still the old, original values and are only changed after a #save or #sync operation.

Syncing Back

After validation, you have two choices: either call #save and let Reform sort out the rest. Or call #sync, which will write all the properties back to the model. In a nested form, this works recursively, of course.

It's then up to you what to do with the updated models - they're still unsaved.

Saving Forms

The easiest way to save the data is to call #save on the form.

    @form.save  #=> populates song with incoming data
                #   by calling @form.song.title= and @form.song.length=.

This will sync the data to the model and then call song.save.

Sometimes, you need to do stuff manually.

Saving Forms Manually

Calling #save with a block doesn't do anything but providing you a nested hash with all the validated input. This allows you to implement the saving yourself.

The block parameter is a nested hash of the form input.

  @form.save do |hash|
    hash      #=> {title: "Rio", length: "366"}

    Song.create(hash)
  end

You can always access the form's model. This is helpful when you were using populators to set up objects when validating.

  @form.save do |nested|
    album = @form.model

    album.update_attributes(nested[:album])
  end

If the form wraps multiple models, via composition, you can access them like this:

  @form.save do |nested|
    song = @form.model[:song]
    label = @form.model[:label]
  end

Note that you can call #sync and then call #save { |hsh| } to save models yourself.

Contracts

Contracts give you a sub-set of the Form API.

  1. #initialize accepts an already populated model.
  2. #validate will run defined validations (without accepting a params hash as in Form).

Contracts can be used to completely remove validation logic from your model classes. Validation should happen in a separate layer - a Contract.

Defining Contracts

A contract looks like a form.

class AlbumContract < Reform::Contract
  property :title
  validates :title, length: {minimum: 9}

  collection :songs do
    property :title
    validates :title, presence: true
  end

It defines the validations and the object graph to be inspected.

In future versions and with the upcoming Trailblazer framework, contracts can be inherited from forms, representers, and cells, and vice-versa. Actually this already works with representer inheritance - let me know if you need help.

Using Contracts

Applying a contract is simple, all you need is a populated object (e.g. an album after #assign_attributes).

album.assign_attributes(..)

contract = AlbumContract.new(album)

if contract.validate
  album.save
else
  raise contract.errors.messages.inspect
end

Contracts help you to make your data layer a dumb persistance tier. My upcoming book discusses that in detail.

Nesting Forms: 1-1 Relations

Songs have artists to compose them. Let's say your Song model would implement that as follows.

class Song < ActiveRecord::Base
  has_one :artist
end

The edit form should allow changing data for artist and song.

class SongForm < Reform::Form
  property :title
  property :length

  property :artist do
    property :name

    validates :name, presence: true
  end

  #validates :title, ...
end

See how simple nesting forms is? By passing a block to ::property you can define another form nested into your main form.

has_one: Setup

This setup's only requirement is having a working Song#artist reader.

class SongsController
  def edit
    song = Song.find(1)
    song.artist #=> <0x999#Artist title="Duran Duran">

    @form = SongForm.new(song)
  end

has_one: Rendering

When rendering this form you could use the form's accessors manually.

= text_field :title,         @form.title
= text_field "artist[name]", @form.artist.name

Or use something like #fields_for in a Rails environment.

= form_for @form do |f|
  = f.text_field :title
  = f.text_field :length

  = f.fields_for :artist do |a|
    = a.text_field :name

has_one: Processing

The block form of #save would give you the following data.

@form.save do |nested|

  nested #=> {title:  "Hungry Like The Wolf",
         #    artist: {name: "Duran Duran"}}
end

Supposed you use reform's automatic save without a block, the following assignments would be made.

form.song.title       = "Hungry Like The Wolf"
form.song.artist.name = "Duran Duran"
form.song.save

Nesting Forms: 1-n Relations

Reform also gives you nested collections.

Let's have Albums with songs!

class Album < ActiveRecord::Base
  has_many :songs
end

The form might look like this.

class AlbumForm < Reform::Form
  property :title

  collection :songs do
    property :title

    validates :title, presence: true
  end
end

This basically works like a nested property that iterates over a collection of songs.

has_many: Rendering

Reform will expose the collection using the #songs method.

= text_field :title,         @form.title
= text_field "songs[0][title]", @form.songs[0].title

However, #fields_for works just fine, again.

= form_for @form do |f|
  = f.text_field :title

  = f.fields_for :songs do |s|
    = s.text_field :title

has_many: Processing

The block form of #save will expose the data structures already discussed.

@form.save do |nested|

  nested #=> {title: "Rio"
         #   songs: [{title: "Hungry Like The Wolf"},
         #          {title: "Last Chance On The Stairways"}]
end

Nesting Configuration

Turning Off Autosave

You can assign Reform to not call save on a particular nested model (per default, it is called automatically on all nested models).

class AlbumForm < Reform::Form
  # ...

  collection :songs, save: false do
    # ..
  end

The :save options set to false won't save models.

Populating Forms For Validation

With a complex nested setup it can sometimes be painful to setup the model object graph.

Let's assume you rendered the following form.

@form = AlbumForm.new(Album.new(songs: [Song.new, Song.new]))

This will render two nested forms to create new songs.

When validating, you're supposed to setup the very same object graph, again. Reform has no way of remembering what the object setup was like a request ago.

So, the following code will fail.

@form = AlbumForm.new(Album.new).validate(params[:album])

However, you can advise Reform to setup the correct objects for you.

class AlbumForm < Reform::Form
  # ...

  collection :songs, populate_if_empty: Song do
    # ..
  end

This works for both property and collection and instantiates Song objects where they're missing when calling #validate.

If you want to create the objects yourself, because you're smarter than Reform, do it with a lambda.

class AlbumForm < Reform::Form
  # ...

  collection :songs, populate_if_empty: lambda { |fragment, args| Song.new } do
    # ..
  end

Compositions

Sometimes you might want to embrace two (or more) unrelated objects with a single form. While you could write a simple delegating composition yourself, reform comes with it built-in.

Say we were to edit a song and the label data the record was released from. Internally, this would imply working on the songs table and the labels table.

class SongWithLabelForm < Reform::Form
  include Composition

  property :title, on: :song
  property :city,  on: :label

  model :song # only needed in ActiveModel context.

  validates :title, :city, presence: true
end

Note that reform needs to know about the owner objects of properties. You can do so by using the on: option.

Also, the form needs to have a main object configured. This is where ActiveModel-methods like #persisted? or '#id' are delegated to. Use ::model to define the main object.

Composition: Setup

The constructor slightly differs.

@form = SongWithLabelForm.new(song: Song.new, label: Label.new)

Composition: Rendering

After you configured your composition in the form, reform hides the fact that you're actually showing two different objects.

= form_for @form do |f|

  Song:     = f.input :title

  Label in: = f.input :city

Composition: Processing

When using `#save' without a block reform will use writer methods on the different objects to push validated data to the properties.

Here's how the block parameters look like.

@form.save do |nested|

  nested #=> {
         #   song:  {title: "Rio"}
         #   label: {city: "London"}
         #   }
end

Forms In Modules

To maximize reusability, you can also define forms in modules and include them in other modules or classes.

module SongsForm
  include Reform::Form::Module

  collection :songs do
    property :title
    validates :title, presence: true
  end
end

This can now be included into a real form.

class AlbumForm < Reform::Form
  property :title

  include SongsForm
end

Note that you can also override properties using inheritance in Reform.

Inheritance

Forms can be derived from other forms and will inherit all properties and validations.

class AlbumForm < Reform::Form
  property :title

  collection :songs do
    property :title

    validates :title, presence: true
  end
end

Now, a simple inheritance can add fields.

class CompilationForm < AlbumForm
  property :composers do
    property :name
  end
end

This will add composers to the existing fields.

You can also partially override fields using :inherit.

class CompilationForm < AlbumForm
  property :songs, inherit: true do
    property :band_id
    validates :band_id, presence: true
  end
end

Using inherit: here will extend the existing songs form with the band_id field. Note that this simply uses representable's inheritance mechanism.

Coercion

Often you want incoming form data to be converted to a type, like timestamps. Reform uses virtus for coercion, the DSL is seamlessly integrated into Reform with the :type option.

Virtus Coercion

Be sure to add virtus to your Gemfile.

require 'reform/form/coercion'

class SongForm < Reform::Form
  include Coercion

  property :written_at, type: DateTime
end

form.validate("written_at" => "26 September")

Coercion only happens in #validate.

form.written_at #=> <DateTime "2014 September 26 00:00">

Manual Coercing Values

If you need to filter values manually, you can override the setter in the form.

class SongForm < Reform::Form
  property :title

  def title=(value)
    super sanitize(value) # value is raw form input.
  end
end

As with the built-in coercion, this setter is only called in #validate.

Virtual Attributes

Virtual fields come in handy when there's no direct mapping to a model attribute or when you plan on displaying but not processing a value.

Virtual Fields

Often, fields like password_confirmation should neither be read from nor written back to the model. Reform comes with the :virtual option to handle that case.

class PasswordForm < Reform::Form
  property :password
  property :password_confirmation, virtual: true

Here, the model won't be queried for a password_confirmation field when creating and rendering the form. When saving the form, the input value is not written to the decorated model. It is only readable in validations and when saving the form manually.

form.validate("password" => "123", "password_confirmation" => "321")

form.password_confirmation #=> "321"

The nested hash in the block-#save provides the same value.

form.save do |nested|
  nested[:password_confirmation] #=> "321"

Read-Only Fields

When you want to show a value but skip processing it after submission the :writeable option is your friend.

class ProfileForm < Reform::Form
  property :country, writeable: false

This time reform will query the model for the value by calling model.country.

You want to use this to display an initial value or to further process this field with JavaScript. However, after submission, the field is no longer considered: it won't be written to the model when saving.

It is still readable in the nested hash and through the form itself.

form.save do |nested|
  nested[:country] #=> "Australia"

Write-Only Fields

A third alternative is to hide a field's value but write it to the database when syncing. This can be achieved using the :readable option.

property :credit_card_number, readable: false

Validations From Models

Sometimes when you still keep validations in your models (which you shouldn't) copying them to a form might not feel right. In that case, you can let Reform automatically copy them.

class SongForm < Reform::Form
  property :title

  extend ActiveModel::ModelValidations
  copy_validations_from Song
end

Note how copy_validations_from copies over the validations allowing you to stay DRY.

This also works with Composition.

class SongForm < Reform::Form
  include Composition
  # ...

  extend ActiveModel::ModelValidations
  copy_validations_from song: Song, band: Band
end

Be warned that we do not encourage copying validations. You should rather move validation code into forms and not work on your model directly anymore.

Agnosticism: Mapping Data

Reform doesn't really know whether it's working with a PORO, an ActiveRecord instance or a Sequel row.

When rendering the form, reform calls readers on the decorated model to retrieve the field data (Song#title, Song#length).

When syncing a submitted form, the same happens using writers. Reform simply calls Song#title=(value). No knowledge is required about the underlying database layer.

The same applies to saving: Reform will call #save on the main model and nested models.

Nesting forms only requires readers for the nested properties as Album#songs.

Rails Integration

Check out @gogogarret's sample Rails app using Reform.

Rails and Reform work together out-of-the-box.

However, you should know about two things.

  1. In case you explicitely don't want to have automatic support for ActiveRecord and form builder: require reform/form, only.
  2. In some setups around Rails 4 the Form::ActiveRecord module is not loaded properly, usually triggering a NoMethodError saying undefined method 'model'. If that happened to you, require 'reform/rails' manually at the bottom of your config/application.rb.

ActiveRecord Compatibility

Reform provides the following ActiveRecord specific features. They're mixed in automatically in a Rails/AR setup.

  • Uniqueness validations. Use validates_uniqueness_of in your form.

As mentioned in the Rails Integration section some Rails 4 setups do not properly load.

You may want to include the module manually then.

class SongForm < Reform::Form
  include Reform::Form::ActiveRecord

ActiveModel Compliance

Forms in Reform can easily be made ActiveModel-compliant.

Note that this step is not necessary in a Rails environment.

class SongForm < Reform::Form
  include Reform::Form::ActiveModel
end

If you're not happy with the model_name result, configure it manually.

class CoverSongForm < Reform::Form
  include Reform::Form::ActiveModel

  model :song
end

This is especially helpful when your framework tries to render cover_song_path although you want to go with song_path.

FormBuilder Support

To make your forms work with all the form gems like simple_form or Rails form_for you need to include another module.

Again, this step is implicit in Rails and you don't need to do it manually.

class SongForm < Reform::Form
  include Reform::Form::ActiveModel
  include Reform::Form::ActiveModel::FormBuilderMethods
end

Simple Form

If you want full support for simple_form do as follows.

class SongForm < Reform::Form
  include ModelReflections

Including this module will add #column_for_attribute and other methods need by form builders to automatically guess the type of a property.

Validations For File Uploads

In case you're processing uploaded files with your form using CarrierWave, Paperclip, Dragonfly or Paperdragon we recommend using the awesome file_validators gem for file type and size validations.

class SongForm < Reform::Form
  property :image

  validates :image, file_size: {less_than: 2.megabytes},
    file_content_type: {allow: ['image/jpeg', 'image/png', 'image/gif']}

Multiparameter Dates

Composed multi-parameter dates as created by the Rails date helper are processed automatically. As soon as Reform detects an incoming release_date(i1) or the like it is gonna be converted into a date.

Note that the date will be nil when one of the components (year/month/day) is missing.

Security

By explicitely defining the form layout using ::property there is no more need for protecting from unwanted input. strong_parameter or attr_accessible become obsolete. Reform will simply ignore undefined incoming parameters.

Nesting Without Inline Representers

When nesting form, you usually use a so-called inline form doing property :song do .. end.

Sometimes you want to specify an explicit form rather than using an inline form. Use the form: option here.

property :song, form: SongForm

The nested SongForm is a stand-alone form class you have to provide.

Overriding Setters For Coercion

When "real" coercion is too much and you simply want to convert incoming data yourself, override the setter.

class SongForm < Reform::Form
  property :title

  def title=(v)
    super(v.upcase)
  end

This will capitalize the title after calling form.validate but before validation happens. Note that you can use super to call the original setter.

Default Values For Presentation

In case you want to change a value for presentation or provide a default value, override the reader. This is only considered when the form is rendered (e.g. in form_for).

class SongForm < Reform::Form
  property :genre

  def genre
    super || 'Punkrock'
  end
end

This will now be used when rendering the view.

= f.input :genre # calls form.genre which provides default.

Dirty Tracker

Every form tracks changes in #validate and allows to check if a particular property value has changed using #changed?.

form.title => "Button Up"

form.validate("title" => "Just Kiddin'")
form.changed?(:title) #=> true

When including Sync::SkipUnchanged, the form won't assign unchanged values anymore in #sync.

Dynamically Syncing And Saving Properties

Both #sync and #save can be configured to run a dynamical lambda per property.

The sync: option allows to statically add a lambda to a property.

property :title, sync: lambda { |value, options| model.set_title(value) }

Instead of running Reform's built-in sync for this property the block is run.

You can also provide the sync lambda at run-time.

form.sync(title: lambda { |value, options| form.model.title = "HOT: #{value}" })

This block is run in the caller's context allowing you to access environment variables. Note that the dynamic sync happens before save, so the model id may be unavailable.

You can do the same for saving.

form.save(title: lambda { |value, options| form.model.title = "#{form.model.id} --> #{value}" })

Again, this block is run in the caller's context.

The two features are an excellent way to handle file uploads without ActiveRecord's horrible callbacks.

Undocumented Features

(Please don't read this section!)

Prepopulating Forms

When rendering a new form for an empty object, nested forms won't show up. The Trailblazer book, chapter 5, discusses this in detail.

You can use the :prepopulate option to configure how to populate a nested form (this also works for scalar properties).

property :song, prepopulate: ->(*) { Song.new } do
  # ..
end

This option is only executed when being instructed to do so, using the #prepopulate! method.

form.prepopulate!

Only do this for forms that are about to get rendered, though.

Collections and partial collection population is covered in chapter 5.

Populator

You can run your very own populator logic if you're keen (and you know what you're doing).

class AlbumForm < Reform::Form
  # ...

  collection :songs, populator: lambda { |fragment, args| args.binding[:form].new(Song.find fragment[:id]) } do
    # ..
  end

Property Inflections

When rendering a form you might need to access the options you provided to property.

property :title, type: String

You can do this using #options_for.

form.options_for(:title) # => {:readable=>true, :coercion_type=>String}

Note that Reform renames some options (e.g. :type internally becomes :coercion_type). Those names are private API and might be changed without deprecation. You better test rendering logic in a unit test to make sure you're forward-compatible.

Support

If you run into any trouble chat with us on irc.freenode.org#trailblazer.

Maintainers

Nick Sutterer

Garrett Heinlen

Attributions!!!

Great thanks to Blake Education for giving us the freedom and time to develop this project in 2013 while working on their project.