rails ModelForm

rails_model_form

module ModelForm
  extend ActiveSupport::Concern

  included do
    class_attribute :model_class
    self.model_class = self.superclass
  end

  module ClassMethods
    def model_name
      model_class.model_name
    end

    def permit(*permitted_attrs)
      @permitted_attrs = permitted_attrs
    end

    def permitted_attrs
      @permitted_attrs
    end

    def wrap(model)
      model.becomes(self).tap do |form|
        form.model = model
      end
    end
  end

  def assign_attributes(attrs = {})
    if attrs.respond_to?(:permitted?)
      attrs = attrs.permit(*self.class.permitted_attrs)
    end
    super(attrs)
  end

  def model
    @model ||= self.becomes(self.class.model_class)
  end

  def model=(value)
    @model = value
  end
end

Usage:

app/models/post.rb

  class Post < ActiveRecord::Base
  end

app/forms/post_form.rb

  class PostForm < Post
    include ModelForm

    validates :text, presence: true

    permit :name, :text
  end

app/controllers/posts_controller.rb

class PostsController < ApplicationController
  def new
    @post_form = PostForm.new
  end

  def create
    @post_form = PostForm.new(params[:post])

    if @post_form.save
      redirect_to @post_form.model
    else
      render :new
    end
  end

  def edit
    @post_form = PostForm.wrap(post)
  end

  def update
    @post_form = PostForm.wrap(post)

    if @post_form.update(params[:post])
      redirect_to @post_form.model
    else
      render :edit
    end
  end

  private

  def post
    @post ||= Post.find(params[:id])
  end
end