A git mirror of the 'pg' gem.
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Latest commit dfc1e08 Oct 22, 2016 @larskanis larskanis Fix typo in JSON#encode
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ext Replace rb_ary_new_from_args() which is missing in Ruby-2.0 Sep 4, 2016
lib Fix typo in JSON#encode Oct 21, 2016
misc Update windows cross compilation tasks to the latest Openssl+Postgres… Jun 17, 2012
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spec Spec: Use a more effective test for default_internal. Sep 4, 2016
.gemtest Converted to Hoe Oct 7, 2011
.hgignore Add errorcodes.def to git in order to allow build from git per bundler. Aug 17, 2016
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.hoerc Add gem cert, trying out gemspec-based setup. Jan 31, 2016
.irbrc Updated build system Jan 3, 2010
.pryrc Rearranging classes under the PG namespace to be a better Ruby citizen Jan 25, 2012
.rvm.gems Bump the rvm gemset gem versions May 14, 2015
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History.rdoc Use secure JSON methods for JSON (de)serialisation. Oct 21, 2016
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POSTGRES fix cross compilation of win32 binary gem, fix mixed case file naming Jan 27, 2012
README-OS_X.rdoc More case-corrections Jan 27, 2012
README-Windows.rdoc Update README-Windows in regards to rake-compiler-dock. Jun 11, 2015
README.ja.rdoc Update READMEs Feb 27, 2013
README.rdoc Merged with upstream Aug 20, 2016
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Rakefile.cross Update OpenSSL and PostgreSQL for binary Windows gems. Aug 13, 2016
appveyor.yml Update Appveyor to use Ruby 2.3 and remove 2.0 and 2.1. Aug 17, 2016
pg.gemspec Correct key+cert upgrade. Aug 20, 2016









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Pg is the Ruby interface to the PostgreSQL RDBMS.

It works with PostgreSQL 9.1 and later.

A small example usage:

#!/usr/bin/env ruby

require 'pg'

# Output a table of current connections to the DB
conn = PG.connect( dbname: 'sales' )
conn.exec( "SELECT * FROM pg_stat_activity" ) do |result|
  puts "     PID | User             | Query"
  result.each do |row|
    puts " %7d | %-16s | %s " %
      row.values_at('procpid', 'usename', 'current_query')

Build Status

Build Status
Travis-CI Build Status Appveyor


  • Ruby 2.2

  • PostgreSQL 9.1.x or later (with headers, -dev packages, etc).

It usually work with earlier versions of Ruby/PostgreSQL as well, but those are not regularly tested.

How To Install

Install via RubyGems:

gem install pg

You may need to specify the path to the 'pg_config' program installed with Postgres:

gem install pg -- --with-pg-config=<path to pg_config>

If you're installing via Bundler, you can provide compile hints like so:

bundle config build.pg --with-pg-config=<path to pg_config>

See README-OS_X.rdoc for more information about installing under MacOS X, and README-Windows.rdoc for Windows build/installation instructions.

There's also a Google+ group and a mailing list if you get stuck, or just want to chat about something.

If you want to install as a signed gem, the public certs of the gem signers can be found in the `certs` directory of the repository.

Type Casts

Pg can optionally type cast result values and query parameters in Ruby or native C code. This can speed up data transfers to and from the database, because String allocations are reduced and conversions in (slower) Ruby code can be omitted.

Very basic type casting can be enabled by:

conn.type_map_for_results = PG::BasicTypeMapForResults.new conn
# ... this works for result value mapping:
conn.exec("select 1, now(), '{2,3}'::int[]").values
    # => [[1, 2014-09-21 20:51:56 +0200, [2, 3]]]

conn.type_map_for_queries = PG::BasicTypeMapForQueries.new conn
# ... and this for param value mapping:
conn.exec_params("SELECT $1::text, $2::text, $3::text", [1, 1.23, [2,3]]).values
    # => [["1", "1.2300000000000000E+00", "{2,3}"]]

But Pg's type casting is highly customizable. That's why it's divided into 2 layers:

Encoders / Decoders (ext/pg_*coder.c, lib/pg/*coder.rb)

This is the lower layer, containing encoding classes that convert Ruby objects for transmission to the DBMS and decoding classes to convert received data back to Ruby objects. The classes are namespaced according to their format and direction in PG::TextEncoder, PG::TextDecoder, PG::BinaryEncoder and PG::BinaryDecoder.

It is possible to assign a type OID, format code (text or binary) and optionally a name to an encoder or decoder object. It's also possible to build composite types by assigning an element encoder/decoder. PG::Coder objects can be used to set up a PG::TypeMap or alternatively to convert single values to/from their string representation.

PG::TypeMap and derivations (ext/pg_type_map*.c, lib/pg/type_map*.rb)

A TypeMap defines which value will be converted by which encoder/decoder. There are different type map strategies, implemented by several derivations of this class. They can be chosen and configured according to the particular needs for type casting. The default type map is PG::TypeMapAllStrings.

A type map can be assigned per connection or per query respectively per result set. Type maps can also be used for COPY in and out data streaming. See PG::Connection#copy_data .


To report bugs, suggest features, or check out the source with Mercurial, check out the project page. If you prefer Git, there's also a Github mirror.

After checking out the source, run:

$ rake newb

This task will install any missing dependencies, run the tests/specs, and generate the API documentation.

The current maintainers are Michael Granger <ged@FaerieMUD.org> and Lars Kanis <lars@greiz-reinsdorf.de>.


Copyright © 1997-2016 by the authors.

  • Jeff Davis <ruby-pg@j-davis.com>

  • Guy Decoux (ts) <decoux@moulon.inra.fr>

  • Michael Granger <ged@FaerieMUD.org>

  • Lars Kanis <lars@greiz-reinsdorf.de>

  • Dave Lee

  • Eiji Matsumoto <usagi@ruby.club.or.jp>

  • Yukihiro Matsumoto <matz@ruby-lang.org>

  • Noboru Saitou <noborus@netlab.jp>

You may redistribute this software under the same terms as Ruby itself; see www.ruby-lang.org/en/about/license.txt or the BSDL file in the source for details.

Portions of the code are from the PostgreSQL project, and are distributed under the terms of the PostgreSQL license, included in the file POSTGRES.

Portions copyright LAIKA, Inc.


See Contributors.rdoc for the many additional fine people that have contributed to this library over the years.

We are thankful to the people at the ruby-list and ruby-dev mailing lists. And to the people who developed PostgreSQL.