Holycorn: PostgreSQL multi-purpose Ruby data wrapper
(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 implement.
Built-in Wrappers
Holycorn is the combination of the mruby VM, some supporting gems (some basic libraries and some more advanced ones), and custom code that implement the actual foreign data wrappers.
All the following wrappers are currently linked against Holycorn:
Redis
, using themruby-redis
gem
INSTALLATION
Prerequisites
- PostgreSQL 9.4+
Setup
Simply run
rake
to vendor and build mruby
.
Now that mruby
is built, building holycorn
requires to run
make
and installing it only requires to run
make install
Now connect to PostgreSQL and install the extension:
位 psql
psql (9.5.14)
Type "help" for help.
DROP EXTENSION holycorn CASCADE;
CREATE EXTENSION holycorn;
Using Builtin Foreign Data Wrappers
Manual Creation of Foreign Tables
A set of builtin FDW are distributed with Holycorn for an easy setup. All one needs to provide are the options that will allow the FDW to be configured:
位 psql
psql (9.5.14)
Type "help" for help.
CREATE SERVER holycorn_server FOREIGN DATA WRAPPER holycorn;
CREATE FOREIGN TABLE redis_table (key text, value text)
SERVER holycorn_server
OPTIONS ( wrapper_class 'HolycornRedis'
, host '127.0.0.1'
, port '6379'
, db '0');
Automatic Import using IMPORT FOREIGN SCHEMA
Alternatively, Holycorn supports IMPORT FOREIGN SCHEMA
and the same can be
accomplished by using that statement instead:
位 psql
psql (9.5.14)
CREATE SERVER holycorn_server FOREIGN DATA WRAPPER holycorn;
IMPORT FOREIGN SCHEMA holycorn_schema
FROM SERVER holycorn_server
INTO holycorn_tables
OPTIONS ( wrapper_class 'HolycornRedis'
, host '127.0.0.1'
, port '6379'
, db '0'
, prefix 'holycorn_'
);
Please note that custom data wrappers have to use the holycorn_schema
schema
as it would otherwise result in an error at runtime.
Note: IMPORT FOREIGN SCHEMA
requires us to use a custom target schema and
Holycorn encourages users to use a prefix
to help avoiding name collisions.
Access Foreign Tables
As Holycorn
doesn't support INSERT
s yet, let's create some manually:
位 redis-cli
127.0.0.1:6379> select 0
OK
127.0.0.1:6379> keys *
(empty list or set)
127.0.0.1:6379> set foo 1
OK
127.0.0.1:6379> set bar 2
OK
127.0.0.1:6379> set baz 3
OK
127.0.0.1:6379> keys *
1) "bar"
2) "foo"
3) "baz"
Now that the table has been created and we have some data in Redis, we can select data from the foreign table.
SELECT * from redis_table;
key | value
-----+-------
bar | 2
foo | 1
baz | 3
(3 rows)
Using custom scripts
Alternatively, custom scripts can be used as the source for a Foreign Data Wrapper:
DROP EXTENSION holycorn CASCADE;
CREATE EXTENSION holycorn;
CREATE SERVER holycorn_server FOREIGN DATA WRAPPER holycorn;
CREATE FOREIGN TABLE holytable (some_date timestamptz) \
SERVER holycorn_server
OPTIONS (wrapper_path '/tmp/source.rb');
(IMPORT FOREIGN SCHEMA
is also supported here.)
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
def import_schema(args = {})
# Keys are:
# * local_schema: the target schema
# * server_name: name of the foreign data server in-use
# * wrapper_class: name of the current class
# * any other OPTIONS passed to IMPORT FOREIGN SCHEMA
end
self
end
For more details about #import_schema
, please take a look at the examples
located in in the builtin_wrappers
directory.
Now you can select data out of the wrapper:
位 psql
psql (9.5.14)
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.
SUPPORTED SCRIPTS
General rules
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
.
Environment
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
SUPPORTED TYPES (Ruby => PG)
Builtin types
MRB_TT_FREE
=>null
MRB_TT_FALSE
=>Boolean
MRB_TT_TRUE
=>Boolean
MRB_TT_FIXNUM
=>Int64
MRB_TT_SYMBOL
=>Text
MRB_TT_UNDEF
=> UnsupportedMRB_TT_FLOAT
=>Float8
MRB_TT_CPTR
=> UnsupportedMRB_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
=> UnsupportedMRB_TT_SCLASS
=> UnsupportedMRB_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
=> UnsupportedMRB_TT_FILE
=> UnsupportedMRB_TT_ENV
=> UnsupportedMRB_TT_DATA
=> See "Arbitraty Ruby objects" sectionMRB_TT_FIBER
=>Text
(inspect
is called)MRB_TT_MAXDEFINE
=> Unsupported
Arbitraty Ruby objects
- Time (Ruby) =>
timestamptz
CONFIGURATION
Server
None (yet).
Foreign Table
Either wrapper_class
or wrapper_path
can be used to defined whether an
external script or a built-in wrapper will manage the foreign table.
wrapper_class
: Name of the built-in wrapper classwrapper_path
: Path of a custom script
In both case, any other option will be pushed down to the wrapper class via the constructor.
TODO
- Array type
- JSON type
- Range type
- Support PG 9.5's
IMPORT FOREIGN SCHEMA
for easy setup
Note on Patches/Pull Requests
- 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.
LICENSE
Copyright (c) 2015-2018 Franck Verrot
Holycorn is an Open Source project licensed under the terms of the LGPLv3 license. Please see http://www.gnu.org/licenses/lgpl-3.0.html for license text.
AUTHOR
Franck Verrot, @franckverrot