Rails - Jul 2005 - Protecting attributes

Hi there,

I''ve recently started using Rails, and I''m already enthousiast
about it!
I keep facing the same problem: I want to proveut an attribute in my 
model from being saved to the database (because it''s a
``date'''' field,
which is default set by my database, which I like) without any luck: my 
database complains about getting a NULL value in the ``date''''
field (in
table special_decla), which violates a non-null constraint:

--- snip ---
ActiveRecord::StatementInvalid in Decla#save_decla

ERROR:  null value in column "date" violates not-null constraint : 
INSERT INTO special_decla ("name", "date",
"amount", "description",
"person_id") VALUES(''test'', NULL, 28.0,
''test'', 1)
--- snip ---

Having read the (well some, not all) docs on rubyonrails.com, I modified 
my code to ``attr_procted :data'''', without any luck. I tried
to
``attr_accessible'''' all the elements which _can_ be saved, but
without
luck too. The only way it works, is by not doing 
``decla.attributes=@param[''decla'']'''', and
explicitly assigning the
attributes. I thought that the protection  of elements of mass 
assignment just should work and that this approach should not be needed, 
hence this mail :-)

I suspect there is something going wrong here, but I do not know what. 
Can anyone point me in the right direction?

I can imagine that it''s perhaps somewhat unusual to
``set_table_name'''',
but the database schema is something beyond my power, and without those 
it simply does not work at all (rails is unable to find my tables).

Some details: I''m using Rails 0.13.1 (debian rails-0.13.1-1 package),
my
database is PostgreSQL and I''m using Ruby 1.8.

the code:

class Decla < ActiveRecord::Base
   set_table_name "special_decla"
   # do not save the date, leave this to the database
   attr_protected :date
   has_one :person
end

class Person < ActiveRecord::Base
   set_table_name "person"
   has_many :declas
end

class DeclaController < ApplicationController
   def save_decla
     item = Decla.new
     item.attributes = @params["decla"]
     if item.save
       redirect_to(:action => "list")
     else
       render_text "Error"
     end
   end
end

best regards,
Jorik Jonker

On 7/21/05, Jorik Jonker <jorik-U9/BOH3cVv3CLqq/8VZgpA@public.gmane.org>
wrote:
> I keep facing the same problem: I want to proveut an attribute in my
> model from being saved to the database (because it''s a
``date'''' field,
> which is default set by my database, which I like) without any luck: my
> database complains about getting a NULL value in the
``date'''' field (in
> table special_decla), which violates a non-null constraint:
I had a similar issue with guid columns in a MS SQL database, I used
the code below to address the issue. It adds a class method
cloak_field to ActiveRecord. I put the code in a cloak.rb file which
is then require from my environment.rb. I am fairly new to Rails, so
if anyone has any suggestions to improve this, please chime in.

pth

---------------------------------------------------------------------

module ActiveRecord
  module Associations
    module ClassMethods
      def cloak_field(*cloaked)
        if (cloaked.length > 0)
          @cloaked_fields = [] unless @cloaked_fields
          @cloaked_fields += cloaked
        end
        @cloaked_fields
      end

      def cloaked_fields
        @cloaked_fields || []
      end
    end
  end

  class Base
    class << self

      # Returns an array of column objects for the table associated
with this class.
      alias :orig_columns :columns
      def columns
        unless @columns
          @columns = orig_columns
          # now mask our our unwanted columns
          @columns.delete_if { |c| cloaked_fields.find { |elem|
elem.to_s == c.name } }
        end
        @columns
      end

    end

    private
      # Initializes the attributes array with keys matching the
columns from the linked table and
      # the values matching the corresponding default value of that column, so
      # that a new instance, or one populated from a passed-in Hash,
still has all the attributes
      # that instances loaded from the database would.
      alias :orig_attributes_from_column_definition
:attributes_from_column_definition
      def attributes_from_column_definition
        result = orig_attributes_from_column_definition
        self.class.cloaked_fields.each { |fld| result.delete(fld.to_s) }
        result
      end

  end
end