Dynamic setting of username and password in database.yml



I’ve now read a lot about application-level authentication in Rails, but
I need to do database-level authentication.

The reason is that my database needs to have the current_user (database
current_user, not current_user defined in an ActiveRecord Model) set to
execute triggers for automatically updating audit tables. So it is not
enough to have a session check against a User table.

How is it possible to set dynamically
values in the database.yml from the application?

I cannot use ActiveRecord::Base.establish_connection in my model because
it does one connect per request, which I think is inefficient and bad
because it leaves connections opened.

Ideally, my application needs to set database-level authentication once,
open one connection and reuse it until the user logs off. Is this
possible with Rails? I thought maybe of using PGconn as described in:


but that does look rather like a hack, or am I wrong?

thanks for any feedback



Hi Isabelle,

I had a similar problem a few weeks ago, I posted to this list, but
this really didn’t solve anything … Anyway, I did what is described
below, and it seems to work. It’s not quite what you want to do, but
it’s heading in the same direction I guess.

Hi everyone,

I am posting this again, as I didn’t get any replies …

I was wondering what the common practice for handling multiple db
users with fine grained privileges on multiple databases is. Against
the often read guideline for rails users to keep with a single db as
“more dbs don’t really make sense anyway”, my opinion is that it DOES
make sense to use more than one db schema for a number of reasons that
I won’t explain here. Anyway, I think a lot of users have to face the
need for multiple dbs, so it should be easy to do it in rails :slight_smile:
shouldn’t it?

I’m working on a project with the goal to put an evaluation system
online. Customers must be able to fill out the answers to the
evaluation questions, and Admins must be able to (1) keep track of all
current evaluations and (2) trigger statistic calculations once
customers complete their evaluation. Customers must not be able to
view/change other Customer’s data, Admins must not be able to change
Customer data but are allowed to view it. These rules MUST be enforced
on the database level. Which leaves me with the facts that

I have an admin and a customer user on my mysql db, and i have three
database schemas called authentication, customer_sandbox and
persistent_base in there as well. The db of most interest is
customer_sandbox. On most of the tables in customer_sandbox only Admin
is allowed to perform CRUD operations. However there is a set of
tables where both Admin and Customer users are allowed CRUD
operations. These tables are the ones where the Customer’s answers to
the evaluation questions are stored. They are a bit tricky because
column privileges restrict access in a way that

  • only Admins are granted INSERT into these tables (make place for new
    evaluation answers)
  • Admins are granted UPDATE only on some of the columns (foreign keys
    and stuff)
  • Customers are granted UPDATE on the rest of the colums (answers to
    the questions - Admins are not allowed to UPDATE those columns)

I currently do the connection configuration in database.yml and I have
different sections for all combinations of database/user pairs, for
all three rails environments. My database.yml looks roughly like this
(the following entries occur for “test” and “production” as well, also
I have the obviously necessary sections labelled development, test and
production with a rather randomly chosen copy of one of my real db
configurations - rails apparently needs these sections, however,
connection details are handled in the model classes, there simply IS
NO default db in my (?any?) multiple db setting)

adapter: mysql
database: ca_authentication
username: webadmin
host: localhost

adapter: mysql
database: ca_sandbox
username: webadmin
host: localhost

adapter: mysql
database: ca_sandbox
username: webadmin
host: localhost

adapter: mysql
database: sandbox
username: customer
host: localhost

adapter: mysql
database: authentication
username: customer
host: localhost

Following Chad F.‘s Rails Recipe on multiple database connections
and Dave T.’ blogentry at
I created a subclass of ActiveRecord::Base to establish a connection
for all models that only webadmin is allowed to CRUD. Although this is
currently not working at the moment (see my previous post to this
list) I’m pretty sure this is the way to go.

The question arises on the set of tables that can be accessed as both
webadmin and customer. I see the following possibilities: (When i say
“default the connection to …” I mean following the above mentioned
rails recipe)

  1. Default the connection of those tables to a customer connection. In
    the WebadminController action performing the “webadmin-only”
    operations, remember the old connection and manually change it to the
    webadmin connection by calling establish_connection. Perform the
    “webadmin-only” operations. Change the connection back to the old one

  2. Same scenario as 1 but vice versa (i.e. defaulting to webadmin and
    changing to customer in the CustomerController)

  3. Create the model classes two times, one time with a superclass
    using a webadmin connection, and one time with a superclass using a
    customer connection. I think it would at least be necessary to give
    rails information about the underlying table name since we need names
    different from the rails convention in order for the classnames not to
    clash (although I think this should be possible to solve using
    modules, then again I don’t know about how models behave in different
    modules). The Controllers referencing those models would need to
    declare precisely which model class they refer to. WebadminController
    would refer to WebadminEvaluationFigureInput and CustomerController
    would refer to CustomerEvaluationFigureInput thus using the same
    table with a different db connection. I am aware that this is not
    really DRY, but I also don’t know which implications on the number of
    open db connections the other 2 possibilities would have, if any. I
    even don’t know if this is working anyway. I will try it out after I
    got some sleep and let you all know! Here is the proposed code

class WebadminSandboxBase < ActiveRecord::Base
establish_connection “webadmin_sandbox_#{RAILS_ENV}”

class CustomerSandboxBase < ActiveRecord::Base
establish_connection “customer_sandbox_#{RAILS_ENV}”

class WebadminEvaluationFigureInput < WebadminSandboxBase
set_table_name “evaluation_figure_inputs”

class CustomerEvaluationFigureInput < CustomerSandboxBase
set_table_name “evaluation_figure_inputs”

class WebadminController < ApplicationController
model :webadmin_evaluation_figure_input

webadmin operations using webadmin db connection


class CustomerController < ApplicationController
model :customer_evaluation_figure_input

customer operations using customer db connection


I would appreciate very much ANY THOUGHTS on how to handle multiple
users on multiple databases with rails! How to properly use the
database.yml to configure connections for multiple users on multiple
database(schemata)? What to do with the default connections needed by
rails (development, test, production sections in the yml) that just
don’t really make sense in such a setting?


Hello Martin

thanks for your prompt reply. Yes, I had read your post, and my problem
is that if I understand your solution, it would mean my application
would require one connection definition for each user, am I correct?


Martin G. wrote:

Hi Isabelle,

I had a similar problem a few weeks ago, I posted to this list, but
this really didn’t solve anything … Anyway, I did what is described
below, and it seems to work. It’s not quite what you want to do, but
it’s heading in the same direction I guess.


Hi Isabelle,

Yes, that was the way i had to go … This is working out ok actually,
i just find this solution a bit verbose and not really DRY. One could
at least argue, that different model class implementations for
different users make sense in a way that most probably these classes
don’t just repeat (duplicate) their definitions, but in fact will have
different access restrictions (thinking of attr_accessible and the
likes, also for authentication libs like ModelSecurity (the one I use)
the declarations will differ). So actually different aspects are
clearly separated, at the cost of being a little WET, not so DRY :slight_smile: I
must say, that I begin to “like” this approach, from a design point of
view, as it moves away from if/else/switch statements to determine
whick connection to use. What do you think?


I forgot something :slight_smile:

The problem with the database.yml still remains. You could configure
this statically for your different user(credentials), like I did (at
the moment). Still, I think that this situation could be enhanced,
keeping in mind 2 things: The database.yml will be preprocessed by
rails, so any ruby code is allowed in there to make things a bit more
dynamic. Also the YAML language is quite powerful, so you could check
out the spec to see if something in there fits the situation. Please
let me know if you find out something!



Jeremy K. wrote:

The issue discussed in this thread sounds like a lot of work with
little benefit.

The world I program in is set up so that the database administrators
create the user and group accounts and access privileges. Triggers for
audit tables are generated upon schema creation by a procedure shared by
all schemas.

All database applications, whether their are webapps, executables,
pipelines etc… have to adapt to this environment.

Rather than implement support for this requirement, I’d work to
eliminate it.

how? Do you mean I should use rails to access the RDMS user table? But
how do I call the triggers without setting current_user?



Chad F. uses ERb to set the socket in his dynamic database config,
but the socket parameter is not set by the rails application:


adapter: mysql
database: DynamicDBConfig_dev
username: root
socket: <% ["/tmp/mysqld.sock",
} %>

we need:

adapter: mysql
database: DynamicDBConfig_dev
username: <% myusername %>
password: <% mypassword %>

somebody posted a similar request before:


but did not get a straight answer. What I would like to do:

1 -rails starts with no database connection
2 -login page prompts user for authentication
3 -login controller tries to set myusername,mypassword parameters for
database.yml, raising error if connection cannot be established
4 -on success, control is passed to rails ModelController
5 -we have a logoff action that calls remove_connection(klass=self)
6 -and a timout mechanism that calls remove_connection(klass=self) to
close the connection if the application is idle

this supposes that the Login class is not an ActivRecord, as we are not
authenticating against a rails Model but against the database native
user management system.

A possible alternative would be to set a default user:

username: <% username ? username : “root” %>
password: <% password ? password : “” %>

and get rails to switch the connection, but that is a bit messy, as we
would always have 2 connections opened.

Rails Gurus, anyone?


On May 10, 2006, at 5:42 AM, iphan iphan wrote:

would always have 2 connections opened.

Rails Gurus, anyone?

The issue discussed in this thread sounds like a lot of work with
little benefit.

Rather than implement support for this requirement, I’d work to
eliminate it.



Hi Martin,

haven’t had time to test that on the webapp level yet, but from the
rails console this seems to be doing what we need:

$ ruby script/console

check default config from database.yml

=> “view_only_account”

close current connection (not sure this is needed)


switch to new user

=> “isabelle”

=> “bozos1”

open connection with new credentials

=> #<ActiveRecord::Base::ConnectionSpecification:0xb79721c8
@config={:username=>“isabelle”, :password=>“bozos1”,
:database=>“keyword_dev”, :host=>“bosnix”, :adapter=>“postgresql”},

now check my application Model has picked up the new credentials

=> #<ActiveRecord::ConnectionAdapters::PostgreSQLAdapter:0xb796c0d4
@config={:username=>“isabelle”, :password=>“bozos1”, etc…}…>