enforce a maximum username length of 25

app/models/user.rb

@@ -27,7 +27,8 @@ class User < ActiveRecord::Base
 
   validates :password, :presence => true, :on => :create
 
-  validates :username, :format => { :with => /\A[A-Za-z0-9][A-Za-z0-9_-]*\Z/ },
+  validates :username,
+    :format => { :with => /\A[A-Za-z0-9][A-Za-z0-9_-]{0,24}\Z/ },
     :uniqueness => { :case_sensitive => false }
 
   validates_each :username do |record,attr,value|
@@ -56,6 +57,12 @@ class User < ActiveRecord::Base
     end
   end
 
+  def self.username_regex
+    User.validators_on(:username).select{|v|
+      v.class == ActiveModel::Validations::FormatValidator }.first.
+      options[:with].inspect
+  end
+
   def as_json(options = {})
     h = super(:only => [
       :username,

app/views/settings/index.html.erb

@@ -14,7 +14,7 @@
       <%= f.label :username, "Username:", :class => "required" %>
       <%= f.text_field :username, :size => 15 %>
       <span class="hint">
-        <tt>[A-Za-z0-9][A-Za-z0-9_-]*</tt>
+        <tt><%= User.username_regex %></tt>
       </span>
     </div>
 

app/views/signup/invited.html.erb

@@ -28,7 +28,7 @@
     <%= f.label :username, "Username:", :class => "required" %>
     <%= f.text_field :username, :size => 30 %>
     <span class="hint">
-      <tt>[A-Za-z0-9][A-Za-z0-9_-]*</tt>
+      <tt><%= User.username_regex %></tt>
     </span>
     <br />