Rails before_validation strip whitespace best practices

There are several gems to do this automatically. Those gems work in the similar way of creating callback in before_validation. One good gem is at https://github.com/holli/auto_strip_attributes

gem "auto_strip_attributes", "~> 2.2"

class User < ActiveRecord::Base
  auto_strip_attributes :name, :nick, nullify: false, squish: true
  auto_strip_attributes :email
end

Stripping is often a good idea. Especially for leading and trailing whitespaces. User often creates trailing spaces when copy/pasting value to a form. With names and other identifying strings you also might want squish the string. So that "Harry    Potter" will become "Harry Potter" (squish option in the gem).

I'd like to add one pitfall that you might experience with the "before_validations" solutions above. Take this example:

u = User.new(name: " lala")
u.name # => " lala"
u.save
u.name # => "lala"

This means you have an inconsistent behavior based on whether your object was saved or not. If you want to address this, I suggest another solution to your problem: overwriting the corresponding setter methods.

class User < ActiveRecord::Base
  def name=(name)
    write_attribute(:name, name.try(:strip))
  end
end

I also like this approach because it does not force you to enable stripping for all attributes that support it - unlike the attribute_names.each mentioned earlier. Also, no callbacks required.

I don't believe before_validation works like that. You probably want to write your method like this instead:

def strip_whitespace
  self.name = self.name.strip unless self.name.nil?
  self.email = self.email.strip unless self.email.nil?
  self.nick = self.nick.strip unless self.nick.nil?
end

You could make it more dynamic if you want using something like self.columns, but that's the gist of it.

Charlie's answer is good, but there's a little verbosity. Here's a tighter version:

def clean_data
  # trim whitespace from beginning and end of string attributes
  attribute_names.each do |name|
    if send(name).respond_to?(:strip)
      send("#{name}=", send(name).strip)
    end
  end
end

The reason we use

self.foo = "bar"

instead of

foo = "bar"

in the context of ActiveRecord objects is that Ruby interprets the latter as a local variable assignment. It will just set the foo variable in your method scope, instead of calling the "foo=" method of your object.

But if you are calling a method, there is no ambiguity. The interpreter knows you're not referring to a local variable called foo because there is none. So for example with:

self.foo = foo + 1

you need to use "self" for the assignment, but not to read the current value.