[chef] Chef for setting the database parameters

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PLEASE NOTE: I have no experience with Chef.  I've been going through the
getting started guides, but I have no idea what I'm doing.

I have a Rails app called Bargain Stock Funds
(http://www.bargainstockfunds.com).  The source code is at
https://github.com/jhsu802701/bsf ;.

My Bargain Stock Funds Rails app uses a custom Ruby gem that I created called
bsf_scrape to download, scrape, process, and save data on each stock fund
covered.  The data is saved to a PostgreSQL database.  As you know, the
database name, username, and password need to be provided when connecting to
the database.

I already have working solutions for providing the database parameters to the
Rails app and Ruby gem.  My Ruby gem bsf_scrape provides the database
parameters in the FundDatabase.rb file at
https://github.com/jhsu802701/bsf_scrape/blob/master/lib/bsf_scrape/FundDatabase.rb
.  These database parameter functions are available externally, as you can see
in the lib/bsf_scrape.rb script at
https://github.com/jhsu802701/bsf_scrape/blob/master/lib/bsf_scrape.rb ;.

My Rails app sets the database parameters in the config/database.yml file by
running the  config/update.rb script
(https://github.com/jhsu802701/bsf/blob/master/config/update.rb).  This script
is automatically run during the deployment process.  And as you can see in the
source code, my Rails app uses the bsf_scrape Ruby gem to set and acquire the
database parameters.

THE BIG QUESTION: How do I go about setting and obtaining the database name,
username, and password through Chef?