Removing conditional logic from a shared partial view or alternative solution - ruby-on-rails

Question

For a current project, I have duplicate code between views, and I'm not sure of the best route to refactor it.
I appear to be in a position where I can have duplicate code across various .html.erb files, or I could put identical code into a partial and use conditionals. I've always heard logic should stay out of views. Neither option seems ideal, and I don't currently know of alternatives.
To illustrate my question, I created a simple rails app called animals. I scaffolded for two models: one for cat and one for dog. Images display their corresponding attributes:
Displaying #cats and #dogs is pretty much the same. Cats just have a column for meows while Dogs have a column for barks, and a dog has the additional attribute column of plays_catch.
Lets say we choose to reduce the duplicate code for displaying cats and dogs by making a shared view partial:
#views/shared/_animal.html.erb
<tr>
<td><%= animal.name %></td>
<td><%= animal.age %> </td>
<% if animal.class == Cat %>
<td><%= animal.meows %> </td>
<% end %>
<% if animal.class == Dog %>
<td><%= animal.barks %> </td>
<td><%= animal.plays_catch %> </td>
<% end %>
</tr>
Then to render #cats = Cat.all:
<%= render partial: "shared/animal", collection: #cats %>
Then to render #dogs = Dog.all:
<%= render partial: "shared/animal", collection: #dogs %>
Obviously it would be overkill to do something like this for this specific example, but the real world project I'm applying it to would not be overkill.
The overall question is: how do you remove nearly identical code that iterates over collections, where the only difference is adding/removing a column of information? It just doesn't feel right to put that logic in the view itself, and leaving the duplication feels wrong.

Answer 1

You could use decorators and add methods that return the extra column(s):
class DogDecorator < Draper::Decorator
def extra_columns
[:barks, plays_catch]
end
end
class CatDecorator < Draper::Decorator
def extra_columns
[:meows]
end
end
...
<% animal.extra_columns.each do |column| %>
<td><%= animal.attributes[column.to_s] %>
<% end %>
...
<% #cats = CatDecorator.decorate_collection(Cat.all)
<%= render partial: "shared/animal", collection: #cats %>

Answer 2

You can use respond_to? to solve the problem more generically. The view logic doesn't feel so wrong when it's more generic.
<% [:meows, :barks, :plays_catch].each do |method| %>
<% if animal.respond_to?(method) %>
<td><%= animal.send(method) %> </td>
<% end %>
<% end %>

Answer 3

You can add a method of the same name to both Cat and Dog classes which would return the specific instance attributes names and values. I'd recommend returning two arrays (one with the names of the fields, other with the fields' values, or vice-versa) since hashes are not exactly ordered. This way you can control the order in which they'll appear in the view.
For example:
#models/cat.rb
def fields_and_attributes
fields = ["Name","Age","Meows"]
attributes = [self.name, self.age]
if self.meows
attributes.push("Yes")
else
attributes.push("No")
end
[fields,attributes] # make sure each attribute is positioned in the same index of its corresponding field
end
#models/dog.rb
def fields_and_attributes
fields = ["Name","Age","Plays catch"]
attributes = [self.name, self.age]
if self.plays_catch
attributes.push("Yes")
else
attributes.push("No")
end
[fields,attributes] # make sure each attribute is positioned in the same index of its corresponding field
end
#controllers/animals_controller.rb
def display_animals
#animals = Cat.all + Dog.all # an array containing the different animals
end
#views/display_animals.html.erb
for i in (0...#animals.size)
fields_and_attributes = #animals[i].fields_and_attributes
for f in (0...fields_and_attributes[0].size)
<p><%= fields_and_attributes[0][f] %> : <%= fields_and_attributes[1][f] %></p>
end
end
Here, we first iterate over all of the animals and call the .fields_and_attributes method of that specific record; we then iterate over the results of calling that method, displaying fields and attributes in the same order as the one defined within the method and also guaranteeing that the code will display every field and every attribute regardless of the difference in the total number of fields for each different animal.

Answer 4

I don't know of any canonical way to accomplish this, but I would use one partial for this in the following way:
<tr>
<% animal.attributes.each do |_, value| %>
<td><%= value %></td>
<% end %>
</tr>
You can get rid of repeated attributes calls by providing in the partial a local variable with pre-obtained model attributes.
EDIT: if you only want to display some attributes.
# Declare whitelist of attributes
# (you can also declare a blacklist and just calculate the difference between two array: all_attributes - blacklist_attributes):
<% whitelist = [:name, :age, :barks] %>
<%= render partial: 'shared/animal',
collection: #dogs,
locals: {attrs: (#dogs.first.attributes.keys.map(&:to_sym) & whitelist)} %>
views/shared/_animal.html.erb:
<tr>
<% attrs.each do |attr| %>
<td><%= animal[attr] %></td>
<% end %>
</tr>

Answer 5

Below is my answer after reviewing posted answers. Basically:
I left the differences within each scaffold model's index page
I made shared partials for common table headers and table data
code below:
#app/views/cats/index.html.erb
<h1>Listing Cats</h1>
<table>
<thead>
<tr>
<%= render partial: "shared/cat_dog_table_headers" %>
<th>Meows</th>
</tr>
</thead>
<tbody>
<% #cats.each do |cat| %>
<tr>
<%= render partial: "shared/cat_dog_table_data", locals: {animal: cat} %>
<td><%= cat.meows %></td>
</tr>
<% end %>
</tbody>
</table>
<br>
<%= link_to 'New Cat', new_cat_path %>
And for the dogs:
#app/views/dogs/index.html.erb
<h1>Listing Dogs</h1>
<table>
<thead>
<tr>
<%= render partial: "shared/cat_dog_table_headers" %>
<th>Barks</th>
<th>Plays catch</th>
</tr>
</thead>
<tbody>
<% #dogs.each do |dog| %>
<tr>
<%= render partial: "shared/cat_dog_table_data", locals: {animal: dog} %>
<td><%= dog.barks %></td>
<td><%= dog.plays_catch %></td>
</tr>
<% end %>
</tbody>
</table>
<br>
<%= link_to 'New Dog', new_dog_path %>
The shared table headers for cats and dogs:
#app/views/shared/_cat_dog_table_headers
<td><%= Name %></td>
<td><%= Age %></td>
The shared table data for cats and dogs:
#app/views/shared/_cat_dog_table_data_headers
<td><%= animal.name %></td>
<td><%= animal.age %></td>