Selecting a database from the application itself?

Rails
1

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

2

On Oct 26, 10:03 am, “[email protected]” [email protected] 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

3

On 10/26/07, [email protected] [email protected] 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

Database

<% form_for :database, @database, :url => {:action => 'set_database'} do |form| %>
Adapter: <%= form.text_field 'adapter' %>
Database: <%= form.text_field 'database' %>
User: <%= form.text_field 'username' %>
Pass: <%= form.text_field 'password' %>
<%= submit_tag 'Switch Database' %> <% end %>

Things

<% @things.each do |thing| %> <% end %>
ID Name
<%= thing.id %> <%= thing.name %>

Create Thing

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

Hope that helps!

Regards,
George.

4

Thank you very much, I will try that :slight_smile: