在Rails快捷方式中检查是否非零且不为空？

Question

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

Answer 1

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.

Answer 2

You can use .present? which comes included with ActiveSupport.

@city = @user.city.present?
# etc ...

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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

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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.