a postgres driver for crystal
0.13.1 released


A native, non-blocking Postgres driver for Crystal

Build Status


This driver now uses the crystal-db project. Documention on connecting, quering, etc, can be found at:



Add this to your shard.yml and run crystal deps

    github: will/crystal-pg


There are two ways to listen for notifications. For docs on NOTIFY, please read

  1. Any connection can be given a callback to run on notifications. However they are only received when other traffic is going on.
  2. A special listen-only connection can be established for instant notification processing with PG.connect_listen.
# see full example in examples/
PG.connect_listen("postgres:///", "a", "b") do |n| # connect and  listen on "a" and "b"
  puts "    got: #{n.payload} on #{}"     # print notifications as they come in


Crystal-pg supports several popular array types. If you only need a 1 dimensional array, you can cast down to the appropriate Crystal type:

PG_DB.query_one("select ARRAY[1, null, 3]", &.read(Array(Int32?))
# => [1, nil, 3]

PG_DB.query_one("select '{hello, world}'::text[]", &.read(Array(String))
# => ["hello", "world"]


Crystal-pg is tested on Postgres versions 9.1 through 9.4 and developed on 9.6 (travis does not currently have 9.5 support). Since it uses protocal version 3, older versions probably also work but are not guaranteed.

Supported Datatypes

  • text
  • boolean
  • int8, int4, int2
  • float4, float8
  • timestamptz, date, timestamp (but no one should use ts when tstz exists!)
  • json and jsonb
  • uuid
  • bytea
  • numeric/decimal (1)
  • varchar
  • regtype
  • geo types: point, box, path, lseg, polygon, circle, line
  • array types: int8, int4, int2, float8, float4, bool, text

1: A note on numeric: In postgres this type has arbitrary percision. In this driver, it is represented as a PG::Numeric which retians all precision, but if you need to do any math on it, you will probably need to cast it to a float first. If you need true abitrary percision, you can optionally require pg_ext/big_rational which adds #to_big_r, but requires that you have LibGMP installed.

  github: greenbigfrog/crystal-pg
  version: ~> 0.13.1
Crystal none

Dependencies 1

  • db ~> 0.3.3
    {'github' => 'crystal-lang/crystal-db', 'version' => '~> 0.3.3'}

Development Dependencies 0

Dependents 1

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