Document the :message option for validates_associated. Closes #10357 [dylans]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8281 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

 *SVN*
 
+* Document the :message option for validates_associated. Closes #10357 [dylans]
+
 * Document automatically generated predicate methods for attributes. Closes #10373 [chuyeow]
 
 * Added ActiveRecord::Base#becomes to turn a record into one of another class (mostly relevant for STIs) [DHH]. Example:

activerecord/lib/active_record/validations.rb

@@ -777,6 +777,7 @@ def validates_exclusion_of(*attr_names)
       # is both present and guaranteed to be valid, you also need to use validates_presence_of.
       #
       # Configuration options:
+      # * <tt>message</tt> - A custom error message (default is: "is invalid")
       # * <tt>on</tt> Specifies when this validation is active (default is :save, other options :create, :update)
       # * <tt>if</tt> - Specifies a method, proc or string to call to determine if the validation should
       #   occur (e.g. :if => :allow_validation, or :if => Proc.new { |user| user.signup_step > 2 }).  The