(m)Ruby + PostgreSQL = <3

Holycorn makes it easy to implement a Foreign Data Wrapper using Ruby.

It is based on top of mruby, that provides sandboxing capabilities the regular Ruby VM "MRI/CRuby" does not provide.

• PostgreSQL 9.1+

Clone and build mruby inside the vendor directory

cd vendor
git clone https://github.com/mruby/mruby.git
cd mruby
make
cd ../..

Building holycorn is as simple as

make

and installing it only requires oneself to

make install

Now you can start setting up the Foreign Data Wrapper:

DROP EXTENSION holycorn CASCADE;
CREATE EXTENSION holycorn;
CREATE SERVER holycorn_server FOREIGN DATA WRAPPER holycorn;
CREATE FOREIGN TABLE holytable (some_date timestampz) \
  SERVER holycorn_server
  OPTIONS (wrapper_path '/tmp/source.rb');

And the source file of the wrapper:

# /tmp/source.rb
class Producer
  def initialize(env = {}) # env contains informations provided by Holycorn
  end

  def each
    @enum ||= Enumerator.new do |y|
      10.times do |t|
        y.yield [ Time.now ]
      end
    end
    @enum.next
  end
  self
end

Now you can select data out of the wrapper:

λ psql
psql (9.4.1)
Type "help" for help.

franck=# SELECT * FROM holytable;
      some_date
---------------------
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
 2015-06-21 22:39:24
(10 rows)

Pretty neat.

Any type of Ruby object can act as a FDW. The only requirements are that it can receive .new (with arity = 1) and return an object that can receive each (arity = 0).

It doesn't have to be a Class, and there's currently no will to provide a superclass to be inherited from.

In future versions, there will be many more callbacks to interact with PG's FDW infrastructure through Holycorn.

Also, the script can only be a single word - like MyClass - as long as MyClass has been defined and exists within your compilation of mruby.

A hash is passed by Holycorn to the Ruby script. Its current keys are:

• PG_VERSION
• PG_VERSION_NUM
• PACKAGE_STRING
• PACKAGE_VERSION
• MRUBY_RUBY_VERSION
• WRAPPER_PATH

• MRB_TT_FREE => null
• MRB_TT_FALSE => Boolean
• MRB_TT_TRUE => Boolean
• MRB_TT_FIXNUM => Int64
• MRB_TT_SYMBOL => Text
• MRB_TT_UNDEF => Unsupported
• MRB_TT_FLOAT => Float8
• MRB_TT_CPTR => Unsupported
• MRB_TT_OBJECT => Text (to_s is called)
• MRB_TT_CLASS => Text (class.to_s is called)
• MRB_TT_MODULE => Text (to_s is called)
• MRB_TT_ICLASS => Unsupported
• MRB_TT_SCLASS => Unsupported
• MRB_TT_PROC => Text (inspect is called)
• MRB_TT_ARRAY => Text (inspect is called)
• MRB_TT_HASH => Text (inspect is called)
• MRB_TT_STRING => Text
• MRB_TT_RANGE => Text (inspect is called)
• MRB_TT_EXCEPTION => Unsupported
• MRB_TT_FILE => Unsupported
• MRB_TT_ENV => Unsupported
• MRB_TT_DATA => See "Arbitraty Ruby objects" section
• MRB_TT_FIBER => Text (inspect is called)
• MRB_TT_MAXDEFINE => Unsupported

• Time (Ruby) => timestampz

TBD;

TBD;

• Array type
• JSON type
• Range type
• Support PG 9.5's IMPORT FOREIGN SCHEMA for easy setup

• Fork the project.
• Make your feature addition or bug fix.
• Add tests for it. This is important so I don't break it in a future version unintentionally.
• Commit, do not mess with version or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
• Send me a pull request. Bonus points for topic branches.

Copyright (c) 2015 Franck Verrot. MIT LICENSE. See LICENSE.md for details.