When Regular Assignment Fails, update_attributes!...?

I've run into my second gotcha with Rails now, solved by the same function: update_attributes!. Both times it took me entirely too long to figure out.

I have a many-to-many assocation, whose proper model implementation is excellently described in the official guide. As expected, my join model :belongs_to each of the models in the many-to-many relationship. We have 3 models, all related to each other; 2 of them are related through the third:



Or, in code:


## in the Receipt class...
:belongs_to :store
:belongs_to :customer

## in the Store class..
:has_many :receipts
:has_many :customers, :through => :receipts

## in the Customer class...
:has_many :receipts
:has_many :stores, :through => :receipts


This ends up being really handy, because we can easily do things with collections owned by either a store or a customer:

@store.receipts.total_price.each do |r|...

Adapting this blog-building example from the Rails guides, led me to create a receipt while building on a store:

@receipt = @store.receipts.build(params[:receipt])

Being new at the time I wrote this code, I figured an easy-enough way to also determine customer ownership of receipts was to extend the assignments:

@receipt = @store.receipts.build(params[:receipt]) = @customer.receipts.build(params[:receipt])

Seems like it should work, but this throws undefined method `build=' errors. I promptly erased that last error-causing bit and headed back to the drawing board -- this time checking the server logs while executing a successful new/create operation. All of my attributes but customer_id were being passed.

Solution: change controller's create method to update the attributes (new portion in bold):


@receipt = @store.receipts.build(params[:receipt])
@receipt.update_attributes!(:customer_id => current_user.id)


Just like that, we're passing all attributes and everything in the @customer.receipts collection is working!

• Note this does assume the excellent RESTful authentication plugin is being used and the user is logged in. Not a problem, since I don't expose my create method to users who aren't logged in, but worth noting nonetheless.

Rails Webapp: Closed Alpha Build

Ever want to use your webapp while it's still a closed alpha? Me too.

My solution is to only let people who have a passphrase create an account. Thanks to a suggestion by Rob125 in freenode's #RubyOnRails channel, I found the easiest way to do this was to modify 3 files.

1. Create a constant in your Rails::Initializer.run do |config| method (config/environment.rb):
   
   Note you'll need to restart your app server for this to take effect.
   
   MY_SECRET_PHRASE = "econometrics is fun!"



2. Add a textbox to your signup form (app/views/users/new.html.erb if using restful_authentication):
   
   <p>What's the passphrase?<br />
<%= text_field_tag 'passphrase' %></p>



3. Compare the constant to your parameter in the create method of the Users controller (app/controllers/users_controller.rb):
   
   @secret = params[:passphrase]
if @secret == MY_SECRET_PHRASE then
  #all that successful stuff...
else
  #all that flash[:error] stuff...
   

And there you have it. Easy to only allow access to a few a people while testing and easy to get rid of when it's time to truly go live. There is a drawback in the form of overhead that comes with an initializer, but certainly it's a fair tradeoff for a quick solution to a temporary problem.

PostgreSQL 'permissions error'

Too many times now I've searched high and low to find the cause of my PostgreSQL 'permissions' error. Certainly it didn't make sense...I had created a superuser and a database with that superuser; PostgreSQL was started;

dropdb dbname

would drop the database and

createdb dbname

would create the database. What was wrong?

In each case I had forgotten something so basic most guides seem to leave it out:

initdb

If you're running Ubuntu and installed PostgreSQL through apt-get, you'll need to initialize your database with the commands below as the user you want to own the data. Generally I make a login with the same name as a database superuser to simplify things.

• Note the folder must also be owned by the user who will own the data.


• Note multiple databases can be stored in this datafolder.

/usr/lib/postgresql/8.4/bin/initdb -D /path/to/datafolder

Ubuntu Karmic 9.10 and ruby-pg

PostgreSQL, Ubuntu, and Rails seem exactly like a winning combination for the type of work I do.

As of this writing (March 12, 2010), the best driver to connect Rails and PostgreSQL is easily ruby-pg. My development environment is Snow Leopard, and my troubles installing ruby-pg on OS X were alleviated by this very helpful article at icoretech.

My server environment of choice is Ubuntu. Getting things up and running had me stumbling a bit again with the ruby-pg gem driver. Turns out the solution is simple -- just install the postgresql-server-dev-8.4 package and the gem installs fine.

The following steps will have PostgreSQL 8.4 and the ruby-pg driver up and running on your Ubuntu Karmic system (assuming you've already installed Ruby)

sudo apt-get install postgresql
sudo apt-get install postgresql-server-dev-8.4
sudo gem install pg