Alter all attributes printed in views on ruby on rails - ruby-on-rails

Question

My rails application only reads data on it's database. There's no save.
Mostly all my views are a form with a few fields to filter my search and a table printing every column's value. Something like that:
<table>
<tr>
<th> Col1 </th>
<th> Col2 </th>
<th> Col3 </th>
...
</tr>
<% Model.all.each do |model| %>
<tr>
<td> <%= model.col1 %> </td>
<td> <%= model.col2 %> </td>
<td> <%= model.col3 %> </td>
...
</tr>
<% end %>
There's over 50 models each with 10-20 fields, almost 100 tables. It's all very straightforward.
Now my client asked me that when any cell is empty (the data is null or '') he wants it to print '-' instead of the blank cell on the table
At first I thought about something like this on my application_helper.rb:
def avoid_empty(object)
if object == nil or object == ""
return "-"
else
return object
end
end
and everywhere on my views I would just change
<%= model.col1 %>
to
<%= avoid_empty(model.col1) %>
but I actually have 2659 lines like that. I'm not sure it's the healthier approach.
Is there any way I can change it everytime I try to print any value from those models that I could go through that method or something similar first, without having to change every single one of my 2659 lines?

Answer 1

You can use the power of ruby's meta-programming and ActiveSupport::Concern.
Create a model extension module to overwrite the getter of all columns dynamically. Below code can do that:
module ModelExtension
extend ActiveSupport::Concern
# To exclude some columns
EXCLUDE_COLUMNS = ['id', 'created_at', 'updated_at']
included do
(self.column_names - EXCLUDE_COLUMNS).each do |col|
define_method col do
self[col].blank? ? '-' : self[col]
end
end
end
end
Include this module in each model to get '-' instead of blank or nil. To include model, you can do:
class MyModel
include ModelExtension
end

Answer 2

You can monkeypatch NilClass.
class NilClass
def to_s
'-'
end
end
Everytime you invoke, say, nil.to_s, it will print '-'. If you type puts nil in the console, will print -. Try the following example:
class NilClass
def to_s
'-'
end
end
foo = nil
foo.to_s #=> '-'
puts foo #=> -
In your case, all occurrences of empty (nil) attributes will output - in the view when trying to print (and, be warned, in other parts of your application too).
PS.: #to_s returns a string representing the instance object.

Answer 3

A solution maybe
The Null Object Pattern
Null Object is an object with some default behavior that implements the same interface as an other object that might be used in a given case. Ok, cool, but how can we apply it to the example below? Let's start with the user method:
def user
#user ||= User.find_by(email: email) || NullUser.new
end
And now we can implement NullUser:
class NullUser
def name
"Anonymous user"
end
end