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https://github.com/will/crystal-pg

a postgres driver for crystal
https://github.com/will/crystal-pg

crystal postgres

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a postgres driver for crystal

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# crystal-pg

A native, non-blocking Postgres driver for Crystal



[![CI](https://github.com/will/crystal-pg/actions/workflows/ci.yml/badge.svg)](https://github.com/will/crystal-pg/actions/workflows/ci.yml)



## 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`



``` yml

dependencies:

  pg:

    github: will/crystal-pg

```



### Example usage



``` crystal

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 .



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`.



``` crystal

# 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:



``` crystal

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.

```Crystal

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](https://github.com/will/crystal-pg/actions)

the Postgres versions the [Postgres project itself supports](https://www.postgresql.org/support/versioning/).

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



``` crystal

 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.