Rails: Scaffold to automatically do one-to-many relationship

Question

Not sure if I'm reading this right, but it seems like Scaffold will not do a one-to-many relationship in its entirety. For instance, if I create messages with scaffold and then I want comments on those messages (one message -> many comments), I have to go through and change everything. For instance, I have to change this in the comment's new view

<% form_for(@comment) do |f| %>

to this

<% form_for([@message, @comment]) do |f| %>

and then change the Action to set up the @message var... amongst other things.

This cannot currently be done automatically with Scaffold, right?

Answer 1

This is true, but, it's not the end of the story. There are at least two alternatives to Scaffold that both work quite well and automatically pick up on relationships between classes (based on your ActiveRecord relationship indicators like has_many). One of these alternatives is Streamlined and the other is ActiveScaffold.

They're mainly helpful for entering in data that your system requires that is not user entered data. For example, I use them for administrative tasks on tables where there's no point in building a complete UI for CRUD when one of the scaffold alternatives will do the job just fine for a seldom used feature. You wouldn't want to use them for comments on messages though.

Answer 2

Yes. Scaffold works for a model and related controller. It does not take care of or work with relationships.

Scaffold's primary objective is to get CRUD going on a model using a controller and related views. That's all. Any other requirement like relationships has to be coded manually.

Answer 3

Note that there are projects like Hobo for Rails which allow you to keep your fields and associations within the model itself. You can't scaffold associations, but it's pretty close.

You end up paying for this sugar by having a lot more of the application built behind your back. Instead of rolling your own, you're usually subtracting out what you need from a large bank of prebuilt behaviors.

Answer 4

You don't need a heavy rails admin framework to get one-to-many relationships working.

You can use scaffolding to get most of the way there.

A little more work in the controller and _form view will get you the rest of the way there.

Here's how...

Story: Select a beer for a developer

In order to select a beer for a developer
As an admin
I want a mainly scaffolded interface to select that beer

Scenario 1: Select beer for new developer
Given I have clicked the <new> button  and entered the developer's name
When I click the beer dropdown
Then I should be presented with a list of beers to choose from
And that beer will be saved when I click <ok>

Scenario 2: Select a different beer for existing developer
Given I have clicked the <edit> button on the index page for a particular developer
When I click the beer dropdown
Then I should be presented with a list of beers to choose from
And that beer will be saved when I click <ok>

Assuming we have a beers table:

  create_table "beers", force: true do |t|
    t.string   "name"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

And a developers table that has a foreign key (beer_id) referencing the beers table:

  create_table "developers", force: true do |t|
    t.string   "name"
    t.integer  "beer_id"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

We can use scaffolding to create both tables:

$ rails g scaffold beer name

$ rails g scaffold developer name beer_id:integer

The scaffold command creates the controllers and views for each model.

We will need to modify our controllers and views a little bit to get the dropdown menu to select a beer for each developer:

app/views/developers/_form.html.erb

Replace the generated text_field and label for beer_id with the following:

  <div class="field">
    <%= f.label :beer_id %><br />
    <%= collection_select(:developer, :beer_id, @beers, :id, :name, {:prompt => false}) %> 
  </div>

app/controllers/developer_controller.rb

Edit the controller's new and edit methods:

  # GET /developers/new
  def new
    @developer = Developer.new
    @beers = Beer.all
    respond_to do |format|
      format.html # new.html.erb
    end
  end


  # GET /developers/1/edit
  def edit
    @beers = Beer.all
    respond_to do |format|
      format.html # new.html.erb
    end    
  end

Screen Shots

Notes

Rails scaffolding is great. Look at all the files that it creates for you:

$ be rails g scaffold beer name
      invoke  active_record
      create    db/migrate/20140912144218_create_beers.rb
      create    app/models/beer.rb
      invoke    rspec
      create      spec/models/beer_spec.rb
      invoke      factory_girl
      create        spec/factories/beers.rb
      invoke  resource_route
       route    resources :beers
      invoke  scaffold_controller
      create    app/controllers/beers_controller.rb
      invoke    erb
      create      app/views/beers
      create      app/views/beers/index.html.erb
      create      app/views/beers/edit.html.erb
      create      app/views/beers/show.html.erb
      create      app/views/beers/new.html.erb
      create      app/views/beers/_form.html.erb
      invoke    rspec
      create      spec/controllers/beers_controller_spec.rb
      create      spec/views/beers/edit.html.erb_spec.rb
      create      spec/views/beers/index.html.erb_spec.rb
      create      spec/views/beers/new.html.erb_spec.rb
      create      spec/views/beers/show.html.erb_spec.rb
      create      spec/routing/beers_routing_spec.rb
      invoke      rspec
      create        spec/requests/beers_spec.rb
      invoke    helper
      create      app/helpers/beers_helper.rb
      invoke      rspec
      create        spec/helpers/beers_helper_spec.rb
      invoke    jbuilder
      create      app/views/beers/index.json.jbuilder
      create      app/views/beers/show.json.jbuilder
      invoke  assets
      invoke    coffee
      create      app/assets/javascripts/beers.js.coffee
      invoke    scss
      create      app/assets/stylesheets/beers.css.scss
      invoke  scss
      create    app/assets/stylesheets/scaffolds.css.scss

All you have to do is know which files to modify when you want more than basic CRUD operations.

Hope that helps. ~ Lex

Answer 5

Scaffolds are scaffolds. When you want anything other than a CRUD on a table (which is what a scaffold is/does), you need to alter the generated scaffolding code, or roll your own.