Check if not nil and not empty in Rails shortcut?
Ruby on-RailsRubyRuby on-Rails Problem Overview
I have a show page for my Users and each attribute should only be visible on that page, if it is not nil and not an empty string. Below I have my controller and it is quite annoying having to write the same line of code @user.city != nil && @user.city != ""
for every variable. I am not too familiar with creating my own methods, but can I somehow create a shortcut to do something like this: @city = check_attr(@user.city)
? Or is there a better way to shorten this procedure?
users_controller.rb
def show
@city = @user.city != nil && @user.city != ""
@state = @user.state != nil && @user.state != ""
@bio = @user.bio != nil && @user.bio != ""
@contact = @user.contact != nil && @user.contact != ""
@twitter = @user.twitter != nil && @user.twitter != ""
@mail = @user.mail != nil && @user.mail != ""
end
Ruby on-Rails Solutions
Solution 1 - Ruby on-Rails
There's a method that does this for you:
def show
@city = @user.city.present?
end
The present?
method tests for not-nil
plus has content. Empty strings, strings consisting of spaces or tabs, are considered not present.
Since this pattern is so common there's even a shortcut in ActiveRecord:
def show
@city = @user.city?
end
This is roughly equivalent.
As a note, testing vs nil
is almost always redundant. There are only two logically false values in Ruby: nil
and false
. Unless it's possible for a variable to be literal false
, this would be sufficient:
if (variable)
# ...
end
This is preferable to the usual if (!variable.nil?)
or if (variable != nil)
stuff that shows up occasionally. Ruby tends to wards a more reductionist type of expression.
One reason you'd want to compare vs. nil
is if you have a tri-state variable that can be true
, false
or nil
and you need to distinguish between the last two states.
Solution 2 - Ruby on-Rails
You can use .present? which comes included with ActiveSupport.
@city = @user.city.present?
# etc ...
You could even write it like this
def show
%w(city state bio contact twitter mail).each do |attr|
instance_variable_set "@#{attr}", @user[attr].present?
end
end
It's worth noting that if you want to test if something is blank, you can use .blank?
(this is the opposite of .present?
)
Also, don't use foo == nil
. Use foo.nil?
instead.