Data Transfer Objects VS Domain/ActiveRecord Entities in the View in RoR

Question

I'm coming from a .NET background, where it is a practice to not bind domain/entity models directly to the view in not-so-basic CRUD-ish applications where the view does not directly project entity fields as-is.

I'm wondering what's the practice in RoR, where the default persistence mechanism is ActiveRecord. I would assert that presentation-related info should not be leaked to the entities, not sure though if this is how real RoR heads would do it.

If DTOs/model per view is the approach, how will you do it in Rails?

Your thoughts?

EDIT:

Some examples:
- A view shows a list of invoices, with the number of unique items in one column.
- A list of credit card accounts, where possibly fraudulent transactions were executed. For that, the UI needs to show this row in red.

For both scenarios, The lists don't show all of the fields of the entities, just a few to show in the list (like invoice #, transaction date, name of the account, the amount of the transaction)

For the invoice example, The invoice entity doesn't have a field "No. of line items" mapped on it. The database has not been denormalized for perf reasons and it will be computed during query time using aggregate functions.

For the credit card accounts example, surely the card transaction entity doesn't have a "Show-in-red" or "IsFraudulent" invariant. Yes it may be a business rule, but for this example, that is a presentation concern, so I would like to keep it out of my domain model.

Answer 1

In general I would answer that your AcitveRecord object can contain any fields and you show in views only what you want. There is scaffolding task in rails scripts but it is only to create some setup model, controller and view. When I work with Rails I don't use ./script/generate scaffold at all. Rather I'm generating only model and controller separatly. The view part I add manualy.

ActiveRecord only maps data from database to some nice objects. What you do with it in view is up to you.

According to separation between presentation and business rules I think that fallowing examples would make it clear to you how to handle it in Rails.

For your invoice example I would create a view this way:

<h1>Invoices</h1>
<table>
  <tr>
    <th>Invoice #</th>
    <th>Date</th>
    <th>Name</th>
    <th>No. of line items</th>
    etc
  </tr>
  <% @invoices.each do |invoice| %>
    <tr>
      <td><%= invoice.number %></td>
      <td><%= invoice.date.to_s %></td>
      <td><%= invoice.name %></td>
      <td><%= invoice.line_items.count %></td>
      etc.
    </tr>
  <% end %>
</table>

Or even put a row with invoice data into separate partial and render it in above view. I assume that in your model you have:

# Invoice model
has_many :line_items

Now lets take a look on credit card example. I would do it like this:

# In CreditCard model add method
def fraudulent?
  #put here some logic that returns true or false
end

Then in your view when you render this credit card:

<div <%= @credit_card.fraudulent? ? 'class="show_in_red"' : '' %>
   here you can show whatever you want
</div>

Or even create helper for it:

# credit card helper
def add_show_in_red(credit_card)
  credit_card.fraudulent? ? 'class="show_in_red"' : ''
end

# in Rails 3 or earlier version with plugin that puts `h` method by default 
# your helper should have additional safe_html! call
def add_show_in_red(credit_card)
  (credit_card.fraudulent? ? 'class="show_in_red"' : '').safe_html!
end

and in view:

<div <%= add_show_in_red(@credit_card) %>>
   here you can show whatever you want
</div>