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 and run shards install

dependencies:
  pg:
    github: will/crystal-pg

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

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.

CrystalDoc.info

pg