Rails - Sep 2009 - ActiveRecord Question: Disabling Boolean Emulation

Hello everyone, I''ve got a question for the ActiveRecord gurus.

ActiveRecord version: 2.3.4
ActiveRecord adapter: mysql

I''m accessing a database originally designed as the back-end data-
store for a Microsoft Access-based GUI application (using "linked"
tables). MS Access, if using linked tables to use a MySQL database
wants its boolean fields, like ActiveRecord, to by TINYINT(1) fields.
However, is makes the field "signed" and uses 0 for false and -1 for
true.

I''ve taken several approaches to interfacing with boolean fields in
this database in an interoperable way (keeping boolean true values as
-1). What seems like it should be so easy/simple has yet yield a clean
solution (to me at least).

My Example Table (tblImages):

ImageID, UNSIGNED INTEGER, AUTOINCREMENT, PRI-KEY
IsFixed, TINYINT, DEFAULT 0

ActiveRecord class:

class Image < ActiveRecord::Base
  set_table_name ''tblImages''
  set_primary_key ''ImageID''
  def fixed
    self.IsFixed_before_type_cast == "-1"
  end
  def fixed=(val)
    self[:IsFixed] = (val ? ''-1'' : ''0'')
  end
end

The above code is just one of the many approaches I''ve taken. I always
get so close yet so far. Reading the value is easy by getting it prior
to type-casting and interpreting it how I want. However, coercing
ActiveRecord (and the MySQL adapter) to issue an "UPDATE tblImage SET
IsFixed = -1 ..." seem all but impossible when I issue a save! on an
instance.

So, is there any way to tell ActiveRecord (or the MySQL adapter) to
simply disable its boolean emulation on a given field (or even the
whole table or database)? Or, does anyone have any alternate ideas
that might work instead or even better?

Thanks for your help!

--
Kendall Gifford

On Wed, Sep 30, 2009 at 6:37 PM, Kendall Gifford
<zettabyte-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> However, coercing
> ActiveRecord (and the MySQL adapter) to issue an "UPDATE tblImage SET
> IsFixed = -1 ..." seem all but impossible when I issue a save! on an
> instance.
Why?  How are you trying and why does it fail?

You can easily change the values in a before_save filter.


-- 
Greg Donald
http://destiney.com/

I believe you can do that in the adapter itself. You should be able to
find it under your activerecord folder (in my PC: C:\ruby\lib\ruby\gems
\1.8\gems\activerecord-2.2.2\lib\active_record\connection_adapters
\mysql_adapter.rb). Look for "class MysqlAdapter < AbstractAdapter"
in
the code and you''ll see this line:

      self.emulate_booleans = true

Change the line to:

      self.emulate_booleans = false

and see what happens.

On Sep 30, 7:37 pm, Kendall Gifford
<zettab...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hello everyone, I''ve got a question for the ActiveRecord gurus.
>
> ActiveRecord version: 2.3.4
> ActiveRecord adapter: mysql
>
> I''m accessing a database originally designed as the back-end data-
> store for a Microsoft Access-based GUI application (using
"linked"
> tables). MS Access, if using linked tables to use a MySQL database
> wants its boolean fields, like ActiveRecord, to by TINYINT(1) fields.
> However, is makes the field "signed" and uses 0 for false and -1
for
> true.
>
> I''ve taken several approaches to interfacing with boolean fields
in
> this database in an interoperable way (keeping boolean true values as
> -1). What seems like it should be so easy/simple has yet yield a clean
> solution (to me at least).
>
> My Example Table (tblImages):
>
> ImageID, UNSIGNED INTEGER, AUTOINCREMENT, PRI-KEY
> IsFixed, TINYINT, DEFAULT 0
>
> ActiveRecord class:
>
> class Image < ActiveRecord::Base
>   set_table_name ''tblImages''
>   set_primary_key ''ImageID''
>   def fixed
>     self.IsFixed_before_type_cast == "-1"
>   end
>   def fixed=(val)
>     self[:IsFixed] = (val ? ''-1'' : ''0'')
>   end
> end
>
> The above code is just one of the many approaches I''ve taken. I
always
> get so close yet so far. Reading the value is easy by getting it prior
> to type-casting and interpreting it how I want. However, coercing
> ActiveRecord (and the MySQL adapter) to issue an "UPDATE tblImage SET
> IsFixed = -1 ..." seem all but impossible when I issue a save! on an
> instance.
>
> So, is there any way to tell ActiveRecord (or the MySQL adapter) to
> simply disable its boolean emulation on a given field (or even the
> whole table or database)? Or, does anyone have any alternate ideas
> that might work instead or even better?
>
> Thanks for your help!
>
> --
> Kendall Gifford