Things we build when we don't read the docs in config/initializers/devise.rb

clean_string_attributes.rb

class User < ActiveRecord::Base
  DO_NOT_MODIFY = ["encrypted_password", "state"]

  def do_not_modify
    DO_NOT_MODIFY
  end
  
  def strip_string_attributes
    string_attributes.each do |k,v|
      # this is a side-effect and mutates instance state
      self.send("#{k}=", v.split.join(" "))
    end
  end

  def string_attributes
    attributes.reject {|k,v| do_not_modify.include?(k) }.
      select {|key, val| val.is_a?(String) }
  end
end

clean_string_attributes_spec.rb

describe "#strip_string_attributes" do
  it "strips whitespace from :name" do
    # User.first.attributes.select {|key, val| val.is_a?(String) }
    # make sure we exclude hashed pw, and state,
    # because we're setting them programmatically
    messy = {
      email: "  [email protected]  ",
      name: "  Whitespace      Username ",
      city: "  White    Space  ",
      postal_code: "  80212    " }
 
    clean = messy.map {|k,v| [k, v.split.join(" ")]}.to_h
 
    user = build_stubbed(:user, messy)
  
    user.strip_string_attributes

    clean.each do |k,v|
      expect(user.send(k)).to eq v
    end
  end
end

devise.rb

# ... in `config/initializers/devise.rb`

# Configure which authentication keys should have whitespace stripped.
# These keys will have whitespace before and after removed upon creating or
# modifying a user and when used to authenticate or find a user. Default is :email.
config.strip_whitespace_keys = [ :email, :name, :city, :postal_code ]

# ^^^ This was literally all I needed to do. Add three keys to an config value.
# Learn from my mistakes, friends, and Read The Fine Documentation™.