Rails - Nov 2007 - using a legacy table with a column named 'type'

I have a legacy database I use to pull data from and one of the 
tables has a column named ''type''.

This cause the following sql to be generated (which doesn''t work):

SELECT * FROM technical_hint WHERE ( (technical_hint.`type` = 
''TechnicalHint'' ) )

If I change the name of the column in the legacy db form
''type'' to
typex''. It works fine and this is what the query looks like:

SELECT * FROM technical_hint

Anybody know waht''s happening and how I can get AR to consider this a 
''non-magic'' name?

Thanks

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

> I have a legacy database I use to pull data from and one of the
> tables has a column named ''type''.
>
> This cause the following sql to be generated (which doesn''t work):
>
> SELECT * FROM technical_hint WHERE ( (technical_hint.`type` >
''TechnicalHint'' ) )
>
> If I change the name of the column in the legacy db form
''type'' to
> typex''. It works fine and this is what the query looks like:
>
> SELECT * FROM technical_hint
>
> Anybody know waht''s happening and how I can get AR to consider
this a
> ''non-magic'' name?
You want the ''inheritance_column''.  There''s an AR
method
''set_inheritance_column'' that you can change it to something
else.

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

At 5:51 PM -0800 11/15/07, Philip Hallstrom wrote:
>You want the ''inheritance_column''.  There''s an AR
method
>''set_inheritance_column'' that you can change it to
something else.
Thanks Phillip,

I was able to do that in my model class for the legacy table with this
statement:

  self.inheritance_column = "type_id"

there is no column named "type_id" in my legacy table and because of
this AR doesn''t try any Single Table Inheritance magic when I access
it.

For anybody interested I keep the models I use for connecting to a legacy
database in a folder in app/models and the models in that folder use an abstract
connection model for communications with the legacy database.

Assuming database.yml has a setting for connecting to a database called:
''legacy_db'' here''s how I''d implement a model
for using the table ''technical_hint'' in the legacy
database". The legacy technical_hint table also has many
technical_hint_implementations and the example below shows how I create the
association.

file app/models/legacy/connection_model.rb:

  class Legacy::ConnectionModel < ActiveRecord::Base
    def self.connection_possible?
      begin
        find(:first)
        true
      rescue SystemCallError, SocketError
        false
      end
    end
    establish_connection :legacy_db
  end

file: app/models/legacy/technical_hint.rb:

  class Legacy::TechnicalHint < Legacy::ConnectionModel
    set_table_name  "technical_hint"
    set_primary_key "technical_hint_id" 
    has_many :technical_hint_implementations,
      :class_name => "Teemss2::TechnicalHintImplementation",
      :foreign_key => "technical_hint_id"
    self.inheritance_column = "type_id"
  end

In the example above the technical_hint table also has a
''type'' column which I need to tell AR to ignore by telling AR
to use a non-existent column name for the the column it uses to do Single Table
Inheritance magic.

This model is referenced like this in an application.

  hints = Legacy::TechnicalHint.find(:all);

Implementing the models this way allows me to:

1) keep all the implementation details about a legacy database well scoped.
2) lets me create first classRrails TechnicalHint model in my application which
won''t conflict with the model from the legacy table.



 for which I am only using the legacy model

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---