Rails - Oct 2007 - Selecting a database from the application itself?

Hi everybody,

I just started thinking about a project and am seeking some help
regarding its design.
The idea would be to create labels (i.e. address labels).I could let
users type the text manually, but I dont think they would appreciate
that when they''ll want to print 5000 addresses.
I can also probably let them import csv files, that should not be a
problem, but playing with those files is not extremely user friendly
either. Besides, I dont want them to get bored after 5 minutes and
going back to their good old excel after 5 minutes.

The most "exciting" feature i thought of is also the one that scares
me the most when it comes to coding:
I''d love to let users actually connect to any database they want,
retrieve a list of tables and fields and let them select anything they
want on the labels.
I can already see the tables with their fields that they could drag
and drop on a label template... Well, I''m dreaming, and I''d
love to
know if this is going to stay just a dream or if this is actually
possible using Ruby and Rails...

Summary : Is there any way I can let users select (from the
application) a database they want to use? Or is the database.yml file
the only way of connecting to a database?

Any help would be greatly appreciated,

Thank you!

Francois


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On Oct 26, 10:03 am, "6ed...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org"
<6ed...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Summary : Is there any way I can let users select (from the
> application) a database they want to use? Or is the database.yml file
> the only way of connecting to a database?
Yes, it is possible but not easy in RoR.

If you can stick to a single database and follow RoR conventions then
life is so much easier.

I arranged things so that I have one server per database, I put the
server name in database.yml:

# This defines the common login info
login: &login
  adapter: mysql
  username: root
  password:
  host: localhost


db1:
  <<: *login
  database: project_db1
  app_server: host.domain.com:4101

db2:
  <<: *login
  database: project_db2
  app_server: host.domain.com:4102


and (re-)read that file with:

APP_CONFIG = YAML::load(File.open("#{RAILS_ROOT}/config/
database.yml"))

I can then use APP_CONFIG[] in a view:

<%= link_to h(project.name), "http://#{APP_CONFIG[project.name]
[''app_server'']}/my_action" %>


It''s a bit hacky but I hope that it gives you some ideas.

Allan


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On 10/26/07, 6edeon-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
<6edeon-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> Summary : Is there any way I can let users select (from the
> application) a database they want to use? Or is the database.yml file
> the only way of connecting to a database?
>
Hi Francois,

Actually, it''s not too hard IMHO.  You certainly don''t need a
different URL / app instance for each database.  In fact, you can pick
a database and run the pending migrations from a before filter in just
a few lines of code.  Here''s a demo:

g@bang:~/tmpapp$ cat db/migrate/001_create_initial_tables.rb
class CreateInitialTables < ActiveRecord::Migration
  def self.up
    create_table :things do |t|
      t.column :name, :string
    end
  end

  def self.down
    drop_table :things
  end
end
g@bang:~/tmpapp$ cat app/models/thing.rb
class Thing < ActiveRecord::Base
end
g@bang:~/tmpapp$ cat app/controllers/things_controller.rb
require ''ostruct''

class ThingsController < ApplicationController
  before_filter :connect_to_database
  def connect_to_database
    config = session[:database] ||= ActiveRecord::Base.configurations[RAILS_ENV]
    ActiveRecord::Base.establish_connection(config)
    ActiveRecord::Migrator.migrate("db/migrate")
    @database = OpenStruct.new(config)
  end

  def set_database
    session[:database] = params[:database]
    redirect_to :action => ''list''
  end

  def list
    @things = Thing.find(:all)
    @thing = Thing.new
  end

  def create
    Thing.create(params[:thing])
    redirect_to :action => ''list''
  end
end
g@bang:~/tmpapp$ cat app/views/things/list.rhtml
<h2>Database</h2>
<% form_for :database, @database,
            :url => {:action => ''set_database''} do
|form| %>
  <table>
    <tr><td>Adapter:</td><td><%= form.text_field
''adapter'' %></td></tr>
    <tr><td>Database:</td><td><%= form.text_field
''database'' %></td></tr>
    <tr><td>User:</td><td><%= form.text_field
''username'' %></td></tr>
    <tr><td>Pass:</td><td><%= form.text_field
''password'' %></td></tr>
  </table>
  <%= submit_tag ''Switch Database'' %>
<% end %>
<hr />

<h2>Things</h2>
<table>
  <tr><th>ID</td><td>Name</td></tr>
  <% @things.each do |thing| %>
    <tr><td><%= thing.id %></td><td><%=
thing.name %></td></tr>
  <% end %>
</table>

<h2>Create Thing</h2>
<% form_for :thing, @thing,
            :url => {:action => ''create''} do |form|
%>
  Name: <%= form.text_field ''name'' %>
  <%= submit_tag ''Create'' %>
<% end %>

Hope that helps!

Regards,
George.

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Thank you very much, I will try that :)

On Oct 26, 5:50 pm, George
<george.og...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On 10/26/07, 6ed...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
<6ed...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>
>
> > Summary : Is there any way I can let users select (from the
> > application) a database they want to use? Or is the database.yml file
> > the only way of connecting to a database?
>
> Hi Francois,
>
> Actually, it''s not too hard IMHO.  You certainly don''t
need a
> different URL / app instance for each database.  In fact, you can pick
> a database and run the pending migrations from a before filter in just
> a few lines of code.  Here''s a demo:
>
> g@bang:~/tmpapp$ cat db/migrate/001_create_initial_tables.rb
> class CreateInitialTables < ActiveRecord::Migration
>   def self.up
>     create_table :things do |t|
>       t.column :name, :string
>     end
>   end
>
>   def self.down
>     drop_table :things
>   end
> end
> g@bang:~/tmpapp$ cat app/models/thing.rb
> class Thing < ActiveRecord::Base
> end
> g@bang:~/tmpapp$ cat app/controllers/things_controller.rb
> require ''ostruct''
>
> class ThingsController < ApplicationController
>   before_filter :connect_to_database
>   def connect_to_database
>     config = session[:database] ||=
ActiveRecord::Base.configurations[RAILS_ENV]
>     ActiveRecord::Base.establish_connection(config)
>     ActiveRecord::Migrator.migrate("db/migrate")
>     @database = OpenStruct.new(config)
>   end
>
>   def set_database
>     session[:database] = params[:database]
>     redirect_to :action => ''list''
>   end
>
>   def list
>     @things = Thing.find(:all)
>     @thing = Thing.new
>   end
>
>   def create
>     Thing.create(params[:thing])
>     redirect_to :action => ''list''
>   end
> end
> g@bang:~/tmpapp$ cat app/views/things/list.rhtml
> <h2>Database</h2>
> <% form_for :database, @database,
>             :url => {:action => ''set_database''} do
|form| %>
>   <table>
>     <tr><td>Adapter:</td><td><%= form.text_field
''adapter'' %></td></tr>
>     <tr><td>Database:</td><td><%=
form.text_field ''database'' %></td></tr>
>     <tr><td>User:</td><td><%= form.text_field
''username'' %></td></tr>
>     <tr><td>Pass:</td><td><%= form.text_field
''password'' %></td></tr>
>   </table>
>   <%= submit_tag ''Switch Database'' %>
> <% end %>
> <hr />
>
> <h2>Things</h2>
> <table>
>   <tr><th>ID</td><td>Name</td></tr>
>   <% @things.each do |thing| %>
>     <tr><td><%= thing.id %></td><td><%=
thing.name %></td></tr>
>   <% end %>
> </table>
>
> <h2>Create Thing</h2>
> <% form_for :thing, @thing,
>             :url => {:action => ''create''} do |form|
%>
>   Name: <%= form.text_field ''name'' %>
>   <%= submit_tag ''Create'' %>
> <% end %>
>
> Hope that helps!
>
> Regards,
> George.

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