Rails - Aug 2005 - single model for multiple tables of same structure

Consider this..

A shopping cart application where each merchant has their own table
for storing product information.  90% of the time the tables schema''s
are the same, but some merchants have added extra columns to their
table.  The table naming scheme is "[merchant_identifier]_products".

There is a single web gui used for all merchants.  The merchant
identifier is available on every page request.  Can a model be created
that dynamically sets the table being used to the naming scheme above?
 Or do I need a new model for each table?

And if I do need a new model,  I''m thinking that I can still use just
one controller to access the different models, assuming that the
models all have the same attributes (columns).  If I know the merchant
identifier, then I also know the model name to use.  What I don''t  is
how to call methods on the model when all I have is a variable holding
the model name.  For example in perl it would be something like this:


my $func = ''test'';
&$func;

sub test {
  print "Function test\n";
}

Which prints "Function test".

I''m completely new to ruby and rails, so if this is pretty basic stuff
forgive me.

Chris

On Tue, 9 Aug 2005, snacktime wrote:
> A shopping cart application where each merchant has their own table for
> storing product information.  90% of the time the tables schema''s
are
> the same, but some merchants have added extra columns to their table.
> The table naming scheme is "[merchant_identifier]_products".
Another way of doing this is to add a key/value table keyed on the product
ID for some merchants. That will solve the "extra fields" problem
without
needing a different schema for each.

e.g. something like:

create table Product_keys (
  product_id int not null,
  merchant_id int not null,
  pk_key varchar not null,
  pk_value varchar(40) not null,
  primary key (product_id, merchant_id, pk_key)
);
> And if I do need a new model, I''m thinking that I can still use
just one
> controller to access the different models, assuming that the models all
> have the same attributes (columns).  If I know the merchant identifier,
> then I also know the model name to use.  What I don''t is how to
call
> methods on the model when all I have is a variable holding the model
> name.  For example in perl it would be something like this:
Sounds way more complicated than my method (and more prone to error in
keeping versions synced).

-- 
_Deirdre  web / blog: http://deirdre.net/
yarn: http://fuzzyorange.com    cat''s blog: http://fuzzyorange.com/vsd/
"Memes are a hoax! Pass it on!"

On 8/9/05, Deirdre Saoirse Moen
<deirdre-mzk6fgDMp2XR7s880joybQ@public.gmane.org>
wrote:
> On Tue, 9 Aug 2005, snacktime wrote:
> 
> > A shopping cart application where each merchant has their own table
for
> > storing product information.  90% of the time the tables
schema''s are
> > the same, but some merchants have added extra columns to their table.
> > The table naming scheme is "[merchant_identifier]_products".
> 
> Another way of doing this is to add a key/value table keyed on the product
> ID for some merchants. That will solve the "extra fields" problem
without
> needing a different schema for each.
> 
> e.g. something like:
> 
> create table Product_keys (
>   product_id int not null,
>   merchant_id int not null,
>   pk_key varchar not null,
>   pk_value varchar(40) not null,
>   primary key (product_id, merchant_id, pk_key)
> );
> 
> > And if I do need a new model, I''m thinking that I can still
use just one
> > controller to access the different models, assuming that the models
all
> > have the same attributes (columns).  If I know the merchant
identifier,
> > then I also know the model name to use.  What I don''t is how
to call
> > methods on the model when all I have is a variable holding the model
> > name.  For example in perl it would be something like this:
> 
> Sounds way more complicated than my method (and more prone to error in
> keeping versions synced).
I agree, but this is an existing system with a large userbase.

We also use postgresql schema''s in some cases for slightly different
reasons (sensitive data that requires extra separation).  In that case
the table names are the same but the schema name is the merchant
identifier.  A solution that worked for my first example would
probably work for this one also.

Chris

snacktime wrote:
>Consider this..
>
>A shopping cart application where each merchant has their own table
>for storing product information.  90% of the time the tables
schema''s
>are the same, but some merchants have added extra columns to their
>table.  The table naming scheme is
"[merchant_identifier]_products".
>
>There is a single web gui used for all merchants.  The merchant
>identifier is available on every page request.  Can a model be created
>that dynamically sets the table being used to the naming scheme above?
> Or do I need a new model for each table?
>
>  
>
class MyBase < ActiveRecord::Base
  @@mi = ''''
 
  def self.mi=(mi)
    @@mi = mi
  end

  def self.mi
    @mi
  end

  def self.set_table_name(table_name)
    super(false) { "#{self.schema}.#{table_name}"}
  end
end

class MyClass < MyBase
  set_table_name ''table_name''
end

and in the controller call MyClass.mi = ''merchant_id''

I do this in my app to rename tables (for another reason) and it works.  
So if what I cobbled together doesn''t work for you, mail me directly.

On 8/9/05, Steve Downey <sldowney-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org>
wrote:
> snacktime wrote:
> 
> >Consider this..
> >
> >A shopping cart application where each merchant has their own table
> >for storing product information.  90% of the time the tables
schema''s
> >are the same, but some merchants have added extra columns to their
> >table.  The table naming scheme is
"[merchant_identifier]_products".
> >
> >There is a single web gui used for all merchants.  The merchant
> >identifier is available on every page request.  Can a model be created
> >that dynamically sets the table being used to the naming scheme above?
> > Or do I need a new model for each table?
> >
> >
> >
> 
> class MyBase < ActiveRecord::Base
>   @@mi = ''''
> 
>   def self.mi=(mi)
>     @@mi = mi
>   end
> 
>   def self.mi
>     @mi
>   end
> 
>   def self.set_table_name(table_name)
>     super(false) { "#{self.schema}.#{table_name}"}
>   end
> end
> 
> class MyClass < MyBase
>   set_table_name ''table_name''
> end
> 
> and in the controller call MyClass.mi = ''merchant_id''
> 
> I do this in my app to rename tables (for another reason) and it works.
> So if what I cobbled together doesn''t work for you, mail me
directly.
Great that''s just what I was looking for.   Thank you.

Chris