Rails - Jun 2007 - A note on multiple databases & associations

Hi,

I have two databases (due to legacy) and have tried the two methods of
having records stored in multiple databases as mentioned in
http://groups.google.com/group/rubyonrails-talk/browse_frm/thread/9b002dee39ecb9f4/06f8856e8a82300e?lnk=gst&q=multiple+database&rnum=3#06f8856e8a82300e

The models are:

Revision:
  belongs_to :project

Project:
  has_many :revision

The tables are:

ProjectDB.projects (storing the Project model)

val_results_development.revisions (to store the Revision models)

So for the first approach to dealing with multiple databases, in
config/database.yml I have:

ProjectsDB:
  adapter: mysql
  database: ProjectsDB
  ...

and in the Project model:

establish_connection "ProjectsDB"

Which all seems to work. It can find projects

But if I do:

Project.find(:all, :include=>:revisions)

I get:

ActiveRecord::StatementInvalid: Mysql::Error: #42S02Table
''ProjectsDB.revisions'' doesn''t exist: SELECT
projects.`id` AS t0_r0,
projects.`name` AS t0_r1, projects.`configfile` AS t0_r2,
projects.`descript` AS t0_r3, projects.`updated` AS t0_r4,
revisions.`id` AS t1_r0, revisions.`tag` AS t1_r1,
revisions.`project_id` AS t1_r2 FROM projects  LEFT OUTER JOIN
revisions ON revisions.project_id = projects.id

It''s looking in the ProjectsDB for the revisions table. The revisions
table actually lives in the database called
''val_results_development''.

There''s a similar problem with
Revision.find(:all,:include=>:project),
it searches for the projects table in the
''val_results_development''
database when it should be looking in the ''ProjectsDB''
database.

OK, so let''s try another approach, in the Project model I say:

set_table_name "ProjectsDB.projects"

and this seems to work, I can get projects from revisions and vice
versa.

But one of the caveats (as described in the Wiki) is that this second
approach won''t work if the database is on another host machine - which
is what I''m going to hit soon!

Does anyone have a way around that, other than resorting to custom
sql? I don''t really want custom sql since I''m hoping to
scaffold much
of the app.

Thanks,

Allan

PS This entry
http://groups.google.com/group/rubyonrails-talk/browse_frm/thread/57e275b63c3e4813/d3151e812114bde5?lnk=gst&q=multiple+database&rnum=9#d3151e812114bde5
suggests that it is not possible, but the set_table_name trick works
as far as I can see.


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Bad form to follow up on one''s own post but I have been thinking ...

On Jun 14, 12:48 pm, Allan
<Allan.Cochr...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> But one of the caveats (as described in the Wiki) is that this second
> approach won''t work if the database is on another host machine -
which
> is what I''m going to hit soon!
>
> Does anyone have a way around that, other than resorting to custom
> sql? I don''t really want custom sql since I''m hoping to
scaffold much
> of the app.
So this isn''t going to work, you can''t access stuff on another
server
in a ''standard'' query.

But it would be nice to not have to use the set_table_name trick.

Allan


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