Tell, Don't Ask when dealing with displaying model attributes or a null replacement

Question

I have the following model:

# == Schema Information # # Table name: clients # # id :integer not null, primary key # first_name :string(255) # last_name :string(255) # email :string(255) # class Client < ActiveRecord::Base def full_name if first_name.blank? && last_name.blank? 'Name: unknown' else first_name + ' ' + last_name end end def email_address email.blank? ? 'Email: unknown' : email end end

Which has the following spec:

RSpec.describe Client, type: :model do describe 'full_name' do it 'should return first_name + last_name if not blank' do @client = create(:client, first_name: 'John', last_name: 'Doe') @client.full_name.should == 'John Doe' end it "should return 'Name: unkonwn' if name is blank" do @client = create(:client, first_name: '', last_name: '') @client.full_name.should == 'Name: unknown' end end describe 'email_address' do it 'should return email if email is not blank' do @client = create(:client, email: '[email protected]') @client.email_address.should == '[email protected]' end it "should return 'Email: unkonwn' if email is blank" do @client = create(:client, email: '') @client.email_address.should == 'Email: unknown' end end end

As you can see I am creating methods (email_address, full_name) to display attributes (or a combination of attributes) in views. If the attribute is blank I want to return a string saying the value is unknown.

I have many more attributes that I would like to display this way, but it seems inefficient to come up with alternative method names for methods that simply return the attribute or the "blank alternative".

As an example, these are some of the other attributes: sex, age, source. Rather than calling client.sex or client.age I would create a method and call client.name_of_sex or client.age_string -- it starts to get awkward (I went from email to email_address in the above example).

The alternative I know is to put logic in my views:

<% if client.email.blank? %> Email: unknown <% else %> <%= client.email %> <% end %>

This is inappropriate for a number of reasons, but my current alternative (the example above) doesn't seem to be optimal.

Is this a point where I should get into making a view-model? Is there some other way I could elegantly perform the actions I want? Or is the way I'm doing it a reasonable thing to do (I'm going to have a lot of attributes I want to display this way)?

Mohamad · Accepted Answer · 2014-12-21 20:17:22Z

I want to offer an alternative to helpers because I believe in this particular case using a presenter to isolate view logic is better than using helpers. As stated yourself you have many more attributes, so having a presenter class avoids having to write generic methods and gives you a scalable way to handle view complexity.

You can use a gem like Draper, or roll your own, which I prefer.

class UserPresenter attr_reader :user, :template def initialize(user, template) @user, @template = user, template end def full_name handle_none user.name, "Name not provided" do user.first_name + ' ' + user.last_name end end def email handle_none user.email, "Email not provided" end def gender handle_none user.gender end private def handle_none(attribute, message = nil, &block) if attribute.present? block_given? ? yield : attribute else message || "Not Available" end end end

Then, using a helper method, you can instantiate this in the view:

 def present(user) presenter = UserPresenter.new(user, self) yield presenter if block_given? presenter end

And in the view:

- present @user do |presenter| = link_to presenter.full_name, @user, class: 'whatever'

tokland · Accepted Answer · 2014-12-11 13:47:14Z

Definitely, this does not belong in the model. The orthodox way is to create a helper. Note how you can use the pattern Object#presence:

module ApplicationHelper def show_field(field, value) value.presence || "#{field}: unknown" end end

And use it in the views:

<%= show_field("Name", user.full_name) %>

You can go a step further and use OOP view presenters if you like the idea (personally I don't use them).

valenterry · Accepted Answer · 2014-12-11 14:38:58Z

I think what you are searching for is an Option type. For more information and an implementation see here and here.

Explaination: Your model seems to have to deal not just with user names only but rather with two cases: there is a user name and there is none. To handle this, you should change your model in that it does not save a user name (as string) and using a blank name as as special case but rather to save a datatype that either contains a user name (as string) or that doesn't.

You can then create a new type that uses an Option type and prints its value if it is there or "unknown" if it is not.

janos · Accepted Answer · 2015-02-14 13:13:06Z

Instead of:

if first_name.blank? && last_name.blank? 'Name: unknown' else first_name + ' ' + last_name end

One who prefers one-liners could do:

"#{first_name} #{last_name}".strip.empty? ? "Name: unknown" : "#{first_name} #{last_name}"

Furthermore, it's better to move such code to a helper method or a decorator using https://github.com/drapergem/draper

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