pg/README.rdoc

= pg

home :: https://github.com/ged/ruby-pg
docs :: http://deveiate.org/code/pg
clog :: link:/History.rdoc

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== Description

Pg is the Ruby interface to the {PostgreSQL RDBMS}[http://www.postgresql.org/].

It works with {PostgreSQL 9.3 and later}[http://www.postgresql.org/support/versioning/].

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('pid', 'usename', 'query')
    end
  end

== Build Status

{<img src="https://github.com/ged/ruby-pg/actions/workflows/source-gem.yml/badge.svg?branch=master" alt="Build Status Github Actions" />}[https://github.com/ged/ruby-pg/actions/workflows/source-gem.yml]
{<img src="https://ci.appveyor.com/api/projects/status/gjx5axouf3b1wicp?svg=true" alt="Build Status Appveyor" />}[https://ci.appveyor.com/project/ged/ruby-pg-9j8l3]
{<img src="https://app.travis-ci.com/larskanis/ruby-pg.svg?branch=master" alt="Build Status" />}[https://app.travis-ci.com/larskanis/ruby-pg]

== Requirements

* Ruby 2.4 or newer
* PostgreSQL 9.3.x or later (with headers, -dev packages, etc).

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


== Versioning

We tag and release gems according to the {Semantic Versioning}[http://semver.org/] principle.

As a result of this policy, you can (and should) specify a dependency on this gem using the {Pessimistic Version Constraint}[http://guides.rubygems.org/patterns/#pessimistic-version-constraint] with two digits of precision.

For example:

  spec.add_dependency 'pg', '~> 1.0'


== 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}[http://goo.gl/TFy1U] and a
{mailing list}[http://groups.google.com/group/ruby-pg] 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}[https://github.com/ged/ruby-pg/tree/master/certs]
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.

The following PostgreSQL column types are supported by ruby-pg (TE = Text Encoder, TD = Text Decoder, BE = Binary Encoder, BD = Binary Decoder):
* Integer: {TE}[rdoc-ref:PG::TextEncoder::Integer], {TD}[rdoc-ref:PG::TextDecoder::Integer], {BD}[rdoc-ref:PG::BinaryDecoder::Integer] 💡 No links? Switch to {here}[https://deveiate.org/code/pg/README_rdoc.html#label-Type+Casts] 💡
  * BE: {Int2}[rdoc-ref:PG::BinaryEncoder::Int2], {Int4}[rdoc-ref:PG::BinaryEncoder::Int4], {Int8}[rdoc-ref:PG::BinaryEncoder::Int8]
* Float: {TE}[rdoc-ref:PG::TextEncoder::Float], {TD}[rdoc-ref:PG::TextDecoder::Float], {BD}[rdoc-ref:PG::BinaryDecoder::Float]
* Numeric: {TE}[rdoc-ref:PG::TextEncoder::Numeric], {TD}[rdoc-ref:PG::TextDecoder::Numeric]
* Boolean: {TE}[rdoc-ref:PG::TextEncoder::Boolean], {TD}[rdoc-ref:PG::TextDecoder::Boolean], {BE}[rdoc-ref:PG::BinaryEncoder::Boolean], {BD}[rdoc-ref:PG::BinaryDecoder::Boolean]
* String: {TE}[rdoc-ref:PG::TextEncoder::String], {TD}[rdoc-ref:PG::TextDecoder::String], {BE}[rdoc-ref:PG::BinaryEncoder::String], {BD}[rdoc-ref:PG::BinaryDecoder::String]
* Bytea: {TE}[rdoc-ref:PG::TextEncoder::Bytea], {TD}[rdoc-ref:PG::TextDecoder::Bytea], {BE}[rdoc-ref:PG::BinaryEncoder::Bytea], {BD}[rdoc-ref:PG::BinaryDecoder::Bytea]
* Base64: {TE}[rdoc-ref:PG::TextEncoder::ToBase64], {TD}[rdoc-ref:PG::TextDecoder::FromBase64], {BE}[rdoc-ref:PG::BinaryEncoder::FromBase64], {BD}[rdoc-ref:PG::BinaryDecoder::ToBase64]
* Timestamp:
  * TE: {local}[rdoc-ref:PG::TextEncoder::TimestampWithoutTimeZone], {UTC}[rdoc-ref:PG::TextEncoder::TimestampUtc], {with-TZ}[rdoc-ref:PG::TextEncoder::TimestampWithTimeZone]
  * TD: {local}[rdoc-ref:PG::TextDecoder::TimestampLocal], {UTC}[rdoc-ref:PG::TextDecoder::TimestampUtc], {UTC-to-local}[rdoc-ref:PG::TextDecoder::TimestampUtcToLocal]
  * BD: {local}[rdoc-ref:PG::BinaryDecoder::TimestampLocal], {UTC}[rdoc-ref:PG::BinaryDecoder::TimestampUtc], {UTC-to-local}[rdoc-ref:PG::BinaryDecoder::TimestampUtcToLocal]
* Date: {TE}[rdoc-ref:PG::TextEncoder::Date], {TD}[rdoc-ref:PG::TextDecoder::Date]
* JSON and JSONB: {TE}[rdoc-ref:PG::TextEncoder::JSON], {TD}[rdoc-ref:PG::TextDecoder::JSON]
* Inet: {TE}[rdoc-ref:PG::TextEncoder::Inet], {TD}[rdoc-ref:PG::TextDecoder::Inet]
* Array: {TE}[rdoc-ref:PG::TextEncoder::Array], {TD}[rdoc-ref:PG::TextDecoder::Array]
* Composite Type (also called "Row" or "Record"): {TE}[rdoc-ref:PG::TextEncoder::Record], {TD}[rdoc-ref:PG::TextDecoder::Record]

The following text formats can also be encoded although they are not used as column type:
* COPY input and output data: {TE}[rdoc-ref:PG::TextEncoder::CopyRow], {TD}[rdoc-ref:PG::TextDecoder::CopyRow]
* Literal for insertion into SQL string: {TE}[rdoc-ref:PG::TextEncoder::QuotedLiteral]
* SQL-Identifier: {TE}[rdoc-ref:PG::TextEncoder::Identifier], {TD}[rdoc-ref:PG::TextDecoder::Identifier]

=== 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 .

The following base type maps are available:
* PG::TypeMapAllStrings - encodes and decodes all values to and from strings (default)
* PG::TypeMapByClass - selects encoder based on the class of the value to be sent
* PG::TypeMapByColumn - selects encoder and decoder by column order
* PG::TypeMapByOid - selects decoder by PostgreSQL type OID
* PG::TypeMapInRuby - define a custom type map in ruby

The following type maps are prefilled with type mappings from the PG::BasicTypeRegistry :
* PG::BasicTypeMapForResults - a PG::TypeMapByOid prefilled with decoders for common PostgreSQL column types
* PG::BasicTypeMapBasedOnResult - a PG::TypeMapByOid prefilled with encoders for common PostgreSQL column types
* PG::BasicTypeMapForQueries - a PG::TypeMapByClass prefilled with encoders for common Ruby value classes


== Contributing

To report bugs, suggest features, or check out the source with Git,
{check out the project page}[https://github.com/ged/ruby-pg].

After checking out the source, install all dependencies:

    $ bundle install

Cleanup extension files, packaging files, test databases:

    $ rake clean

Compile extension:

    $ rake compile

Run tests/specs with PostgreSQL tools like `initdb` in the path:

    $ PATH=$PATH:/usr/lib/postgresql/14/bin rake test

Or run a specific test with the line number:

    $ PATH=$PATH:/usr/lib/postgresql/14/bin rspec -Ilib -fd spec/pg/connection_spec.rb:455

Generate the API documentation:

    $ rake docs

Make sure, that all bugs and new features are verified by tests.

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


== Copying

Copyright (c) 1997-2022 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
https://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.


== Acknowledgments

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.