From: Todd Benson <caduceass@...>
Date: 2007-07-27T00:22:08+09:00
Subject: Re: Array access

On 7/26/07, Alvaro Perez <alvaro.pmartinez@gmail.com> wrote:
> Nothing special with my class:
>
> class Target < ActiveRecord::Base
>
>    attr_accessor :hit_sequence_accession,
>                  :hit_sequence_desc,
>                  :hit_sequence_ID
>
>    def initialize(hit_sequence_accession,
>                hit_sequence_desc,
>                hit_sequence_ID)
>    @hit_sequence_accession = hit_sequence_accession
>    @hit_sequence_desc = hit_sequence_desc
>    @hit_sequence_ID = hit_sequence_ID
>    end
>
> end
>
> There's no targets table in the DB. i'm trying to create a custom dto
> class with data from two tables:
>
> @targets = Target.find_by_sql("SELECT hit_sequence_accession,
> hit_sequence_desc, " +
>   "hit_sequence_ID FROM hit_sequence " +
>   "JOIN sequence_db USING(sequence_db_ID) ")
>
>    But doing:
>
> p @targets[0].attributes["hit_sequence_ID"]
>
>    gets me this error messagge:
>
>
> ActiveRecord::StatementInvalid in SearchController#do_search_targets
>
> Mysql::Error: #42S02Table 'srnadb_chlamy_dev_rails.targets' doesn't
> exist: SHOW FIELDS FROM targets

Hmm, no doubt you would receive some good help from activerecord gurus
on the rails list.

A couple of thoughts...

An ActiveRecord::Base object needs to have a relation (table) in the
database because many of its methods query the database (AFAIK).

Your instance variables of Target that you set with attr_accessor have
nothing to do with the @attributes variable provided by
ActiveRecord::Base.  In fact, you broke the accessor methods Base
provides when you created your instance variables, which is why you
got nil with @targets[0].hit_sequence_ID.  The object was returning
the instance variable and not executing the accessor _method_.

If you don't specifically need a homemade object to hold your queried
data, you can just...

targets = ActiveRecord::Base.find_by_sql(<your query here>)

I have no idea of your database schema, but you could do this if you
want a Target object...

class Target < ActiveRecord::Base
  set_table_name 'sequence_db'
end

targets = Target.find_by_sql(<your query here>)
targets.first.hit_sequence_ID

But, that is hardly the activerecord way.  You should really specify
your Base class relations with has_many, belongs_to, etc.

Todd