pg
crystal-pg
A native, non-blocking Postgres driver for Crystal
usage
This driver now uses the crystal-db project. Documentation on connecting,
querying, etc, can be found at:
- https://crystal-lang.org/docs/database/
- https://crystal-lang.org/docs/database/connection_pool.html
shards
Add this to your shard.yml on a generated crystal project,
and run shards install
dependencies:
pg:
github: will/crystal-pg
Example usage
require "db"
require "pg"
DB.open("postgres://user:pass@host:port/db_name?option1=a&option2=b") do |db|
... use db ...
end
More
crystal-pg also supports some functionality past the typical crystal-db usage:
Listen/Notify
There are two ways to listen for notifications. For docs on NOTIFY, please
read https://www.postgresql.org/docs/current/static/sql-notify.html.
- Any connection can be given a callback to run on notifications. However they are only received when other traffic is going on.
- A special listen-only connection can be established for instant notification
processing with
PG.connect_listen.
# see full example in examples/listen_notify.cr
PG.connect_listen("postgres:///", "a", "b") do |n| # connect and listen on "a" and "b"
puts " got: #{n.payload} on #{n.channel}" # print notifications as they come in
end
Arrays
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"]
Error Handling
It is possible to catch errors and notifications and pass them along to Crystal for further handling.
DB.connect("postgres:///") do |cnn|
# Capture and print all exceptions
cnn.on_notice { |x| puts "pgSQL #{x}" }
# A function that raises exceptions
cnn.exec(
<<-SQL
CREATE OR REPLACE FUNCTION foo(IN str TEXT)
RETURNS VOID
LANGUAGE 'plpgsql'
AS $$
BEGIN
IF str = 'yes' THEN
RAISE NOTICE 'Glad we agree!';
ELSE
RAISE EXCEPTION 'You know nothing John Snow!';
END IF;
END;
$$;
SQL
)
# Notice handling example
cnn.exec(
<<-SQL
SELECT foo('yes');
SQL
)
# => pgSQL NOTICE: Glad we agree!
# Exception handling example
cnn.exec(
<<-SQL
SELECT foo('no');
SQL
)
# => pgSQL ERROR: You know nothing John Snow!
# Unhandled exception: You know nothing John Snow! (PQ::PQError)
# from lib/pg/src/pq/connection.cr:203:7 in 'handle_error'
# from lib/pg/src/pq/connection.cr:186:7 in 'handle_async_frames'
# from lib/pg/src/pq/connection.cr:162:7 in 'read'
# from lib/pg/src/pq/connection.cr:386:18 in 'expect_frame'
# from lib/pg/src/pq/connection.cr:370:9 in 'read_next_row_start'
# from lib/pg/src/pg/result_set.cr:39:8 in 'move_next'
# from lib/pg/src/pg/statement.cr:39:13 in 'perform_exec'
# from lib/db/src/db/statement.cr:82:14 in 'perform_exec_and_release'
# from lib/db/src/db/statement.cr:68:7 in 'exec:args'
# from lib/db/src/db/query_methods.cr:271:7 in 'exec'
# from spec/cerebrum_spec.cr:84:3 in '__crystal_main'
# from /usr/share/crystal/src/crystal/main.cr:97:5 in 'main_user_code'
# from /usr/share/crystal/src/crystal/main.cr:86:7 in 'main'
# from /usr/share/crystal/src/crystal/main.cr:106:3 in 'main'
# from __libc_start_main
# from _start
# from ???
Requirements
Crystal-pg is regularly tested on the Postgres versions the Postgres project itself supports. Since it uses protocol 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, numeric, timestamptz, date, timestamp
- interval (2)
1: A note on numeric: In Postgres this type has arbitrary precision. In this
driver, it is represented as a PG::Numeric which retains 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 arbitrary precision, you can optionally
require pg_ext/big_rational which adds #to_big_r, but requires that you
have LibGMP installed.
2: A note on interval: A Postgres interval can not be directly mapped to a built
in Crystal datatype. Therfore we provide a PG::Interval type that can be converted to
Time::Span and Time::MonthSpan.
Authentication Methods
By default this driver will accept scram-sha-256 and md5, as well as
trust. However cleartext is disabled by default. You can control exactly
which auth methods the client will accept by passing in a comma separated list
to the auth_methods parameter, for example
DB.open("postgres://example.com/dbname?auth_methods=cleartext,md5,scram-sha-256")
DO NOT TURN cleartext ON UNLESS YOU ABSOLUTELY NEED IT! Merely by having
this option enabled exposes a postgres client to downgrade man-in-the-middle
attacks, even if the server is configured to not support cleartext. Even if you
use TLS, you are not safe unless you are fully verifying the server's cert, as
the attacker can terminate TLS and re-negotiate a connection with the server.
client attacker server
----------------------------------------------------------------------------
I want to connect \
\-> intercepts, forwards
I want to connect \
\-----> receives connection request
/ I support scram and/or md5 only
intercepts, sends <-/
/ I only support cleartext
receives attacker <-/
claiming server
only supports cleartext
sends password because
cleartext enabled \
\-> receives clear password,
negotiates scram/md5
with real server \
\--> accepts scram/md5 auth
It is a mistake for any driver to support cleartext by default, and it's a mistake that postgres continues to have this as an option at all.