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Mojo::Pg

Section: User Contributed Perl Documentation (3)
Updated: 2019-01-20
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NAME

Mojo::Pg - Mojolicious X PostgreSQL

SYNOPSIS

  use Mojo::Pg;  # Use a PostgreSQL connection string for configuration  my $pg = Mojo::Pg->new('postgresql://postgres@/test');  # Select the server version  say $pg->db->query('select version() as version')->hash->{version};  # Use migrations to create a table  $pg->migrations->name('my_names_app')->from_string(<<EOF)->migrate;  -- 1 up  create table names (id serial primary key, name text);  -- 1 down  drop table names;  EOF  # Use migrations to drop and recreate the table  $pg->migrations->migrate(0)->migrate;  # Get a database handle from the cache for multiple queries  my $db = $pg->db;  # Use SQL::Abstract to generate simple CRUD queries for you  $db->insert('names', {name => 'Isabell'});  my $id = $db->select('names', ['id'], {name => 'Isabell'})->hash->{id};  $db->update('names', {name => 'Belle'}, {id => $id});  $db->delete('names', {name => 'Belle'});  # Insert a few rows in a transaction with SQL and placeholders  eval {    my $tx = $db->begin;    $db->query('insert into names (name) values (?)', 'Sara');    $db->query('insert into names (name) values (?)', 'Stefan');    $tx->commit;  };  say $@ if $@;  # Insert another row with SQL::Abstract and return the generated id  say $db->insert('names', {name => 'Daniel'}, {returning => 'id'})->hash->{id};  # JSON roundtrip  say $db->query('select ?::json as foo', {json => {bar => 'baz'}})    ->expand->hash->{foo}{bar};  # Select all rows blocking with SQL::Abstract  say $_->{name} for $db->select('names')->hashes->each;  # Select all rows non-blocking with SQL::Abstract  $db->select('names' => sub {    my ($db, $err, $results) = @_;    die $err if $err;    say $_->{name} for $results->hashes->each;  });  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;  # Concurrent non-blocking queries (synchronized with promises)  my $now   = $pg->db->query_p('select now() as now');  my $names = $pg->db->query_p('select * from names');  Mojo::Promise->all($now, $names)->then(sub {    my ($now, $names) = @_;    say $now->[0]->hash->{now};    say $_->{name} for $names->[0]->hashes->each;  })->catch(sub {    my $err = shift;    warn "Something went wrong: $err";  })->wait;  # Send and receive notifications non-blocking  $pg->pubsub->listen(foo => sub {    my ($pubsub, $payload) = @_;    say "foo: $payload";    $pubsub->notify(bar => $payload);  });  $pg->pubsub->listen(bar => sub {    my ($pubsub, $payload) = @_;    say "bar: $payload";  });  $pg->pubsub->notify(foo => 'PostgreSQL rocks!');  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

DESCRIPTION

Mojo::Pg is a tiny wrapper around DBD::Pg that makesPostgreSQL <http://www.postgresql.org> a lot of fun to use with theMojolicious <https://mojolicious.org> real-time web framework. Perform queriesblocking and non-blocking, use allSQL features <https://www.postgresql.org/docs/current/static/sql.html>PostgreSQL has to offer, generate CRUD queries from data structures, manage yourdatabase schema with migrations and build scalable real-time web applicationswith the publish/subscribe pattern.

BASICS

Database and statement handles are cached automatically, and will be reusedtransparently to increase performance. You can handle connection timeoutsgracefully by holding on to them only for short amounts of time.

  use Mojolicious::Lite;  use Mojo::Pg;  helper pg => sub { state $pg = Mojo::Pg->new('postgresql://postgres@/test') };  get '/' => sub {    my $c  = shift;    my $db = $c->pg->db;    $c->render(json => $db->query('select now() as now')->hash);  };  app->start;

In this example application, we create a "pg" helper to store a Mojo::Pgobject. Our action calls that helper and uses the method ``db'' in Mojo::Pg todequeue a Mojo::Pg::Database object from the connection pool. Then we use themethod ``query'' in Mojo::Pg::Database to execute anSQL <http://www.postgresql.org/docs/current/static/sql.html> statement, whichreturns a Mojo::Pg::Results object. And finally we call the method``hash'' in Mojo::Pg::Results to retrieve the first row as a hash reference.

While all I/O operations are performed blocking, you can wait for long runningqueries asynchronously, allowing the Mojo::IOLoop event loop to performother tasks in the meantime. Since database connections usually have a very lowlatency, this often results in very good performance.

Every database connection can only handle one active query at a time, thisincludes asynchronous ones. To perform multiple queries concurrently, you haveto use multiple connections.

  # Performed concurrently (5 seconds)  $pg->db->query('select pg_sleep(5)' => sub {...});  $pg->db->query('select pg_sleep(5)' => sub {...});

All cached database handles will be reset automatically if a new process hasbeen forked, this allows multiple processes to share the same Mojo::Pgobject safely.

GROWING

And as your application grows, you can move queries into model classes.

  package MyApp::Model::Time;  use Mojo::Base -base;  has 'pg';  sub now { shift->pg->db->query('select now() as now')->hash }  1;

Which get integrated into your application with helpers.

  use Mojolicious::Lite;  use Mojo::Pg;  use MyApp::Model::Time;  helper pg => sub { state $pg = Mojo::Pg->new('postgresql://postgres@/test') };  helper time => sub { state $time = MyApp::Model::Time->new(pg => shift->pg) };  get '/' => sub {    my $c = shift;    $c->render(json => $c->time->now);  };  app->start;

EXAMPLES

This distribution also contains two greatexampleapplications <https://github.com/mojolicious/mojo-pg/tree/master/examples/>you can use for inspiration. The minimalchat <https://github.com/mojolicious/mojo-pg/tree/master/examples/chat.pl>application will show you how to scale WebSockets to multiple servers, and thewell-structuredblog <https://github.com/mojolicious/mojo-pg/tree/master/examples/blog>application how to apply the MVC design pattern in practice.

EVENTS

Mojo::Pg inherits all events from Mojo::EventEmitter and can emit thefollowing new ones.

connection

  $pg->on(connection => sub {    my ($pg, $dbh) = @_;    ...  });

Emitted when a new database connection has been established.

  $pg->on(connection => sub {    my ($pg, $dbh) = @_;    $dbh->do('set search_path to my_schema');  });

ATTRIBUTES

Mojo::Pg implements the following attributes.

abstract

  my $abstract = $pg->abstract;  $pg          = $pg->abstract(SQL::Abstract::Pg->new);

SQL::Abstract::Pg object used to generate CRUD queries forMojo::Pg::Database, defaults to enabling "array_datatypes" and setting"name_sep" to "." and "quote_char" to """.

  # Generate WHERE clause and bind values  my($stmt, @bind) = $pg->abstract->where({foo => 'bar', baz => 'yada'});

auto_migrate

  my $bool = $pg->auto_migrate;  $pg      = $pg->auto_migrate($bool);

Automatically migrate to the latest database schema with ``migrations'', assoon as ``db'' has been called for the first time.

database_class

  my $class = $pg->database_class;  $pg       = $pg->database_class('MyApp::Database');

Class to be used by ``db'', defaults to Mojo::Pg::Database. Note that thisclass needs to have already been loaded before ``db'' is called.

dsn

  my $dsn = $pg->dsn;  $pg     = $pg->dsn('dbi:Pg:dbname=foo');

Data source name, defaults to "dbi:Pg:".

max_connections

  my $max = $pg->max_connections;  $pg     = $pg->max_connections(3);

Maximum number of idle database handles to cache for future use, defaults to1.

migrations

  my $migrations = $pg->migrations;  $pg            = $pg->migrations(Mojo::Pg::Migrations->new);

Mojo::Pg::Migrations object you can use to change your database schema moreeasily.

  # Load migrations from file and migrate to latest version  $pg->migrations->from_file('/home/sri/migrations.sql')->migrate;

options

  my $options = $pg->options;  $pg         = $pg->options({AutoCommit => 1, RaiseError => 1});

Options for database handles, defaults to activating "AutoCommit","AutoInactiveDestroy" as well as "RaiseError" and deactivating "PrintError"as well as "PrintWarn". Note that "AutoCommit" and "RaiseError" areconsidered mandatory, so deactivating them would be very dangerous.

parent

  my $parent = $pg->parent;  $pg        = $pg->parent(Mojo::Pg->new);

Another Mojo::Pg object to use for connection management, instead ofestablishing and caching our own database connections.

password

  my $password = $pg->password;  $pg          = $pg->password('s3cret');

Database password, defaults to an empty string.

pubsub

  my $pubsub = $pg->pubsub;  $pg        = $pg->pubsub(Mojo::Pg::PubSub->new);

Mojo::Pg::PubSub object you can use to send and receive notifications veryefficiently, by sharing a single database connection with many consumers.

  # Subscribe to a channel  $pg->pubsub->listen(news => sub {    my ($pubsub, $payload) = @_;    say "Received: $payload";  });  # Notify a channel  $pg->pubsub->notify(news => 'PostgreSQL rocks!');

search_path

  my $path = $pg->search_path;  $pg      = $pg->search_path(['$user', 'foo', 'public']);

Schema search path assigned to all new connections.

  # Isolate tests and avoid race conditions when running them in parallel  my $pg = Mojo::Pg->new('postgresql:///test')->search_path(['test_one']);  $pg->db->query('drop schema if exists test_one cascade');  $pg->db->query('create schema test_one');  ...  $pg->db->query('drop schema test_one cascade');

username

  my $username = $pg->username;  $pg          = $pg->username('sri');

Database username, defaults to an empty string.

METHODS

Mojo::Pg inherits all methods from Mojo::EventEmitter and implements thefollowing new ones.

db

  my $db = $pg->db;

Get a database object based on ``database_class'' (which is usuallyMojo::Pg::Database) for a cached or newly established database connection.The DBD::Pg database handle will be automatically cached again when thatobject is destroyed, so you can handle problems like connection timeoutsgracefully by holding on to it only for short amounts of time.

  # Add up all the money  say $pg->db->select('accounts')    ->hashes->reduce(sub { $a->{money} + $b->{money} });

from_string

  $pg = $pg->from_string('postgresql://postgres@/test');  $pg = $pg->from_string(Mojo::Pg->new);

Parse configuration from connection string or use another Mojo::Pg object as``parent''.

  # Just a database  $pg->from_string('postgresql:///db1');  # Just a service  $pg->from_string('postgresql://?service=foo');  # Username and database  $pg->from_string('postgresql://sri@/db2');  # Short scheme, username, password, host and database  $pg->from_string('postgres://sri:s3cretAATTlocalhost/db3');  # Username, domain socket and database  $pg->from_string('postgresql://sri@%2ftmp%2fpg.sock/db4');  # Username, database and additional options  $pg->from_string('postgresql://sri@/db5?PrintError=1&pg_server_prepare=0');  # Service and additional options  $pg->from_string('postgresql://?service=foo&PrintError=1&RaiseError=0');  # Username, database, an option and search_path  $pg->from_string('postgres://sri@/db6?&PrintError=1&search_path=test_schema');

new

  my $pg = Mojo::Pg->new;  my $pg = Mojo::Pg->new('postgresql://postgres@/test');  my $pg = Mojo::Pg->new(Mojo::Pg->new);

Construct a new Mojo::Pg object and parse connection string with``from_string'' if necessary.

  # Customize configuration further  my $pg = Mojo::Pg->new->dsn('dbi:Pg:service=foo');

DEBUGGING

You can set the "DBI_TRACE" environment variable to get some advanceddiagnostics information printed by DBI.

  DBI_TRACE=1  DBI_TRACE=15  DBI_TRACE=SQL

REFERENCE

This is the class hierarchy of the Mojo::Pg distribution.

*: Mojo::Pg
*: Mojo::Pg::Database
*: Mojo::Pg::Migrations
*: Mojo::Pg::PubSub
*: Mojo::Pg::Results
*: Mojo::Pg::Transaction
*: SQL::Abstract::Pg

AUTHOR

Sebastian Riedel, "sriAATTcpan.org".

CREDITS

In alphabetical order:

Christopher Eveland

Dan Book

Flavio Poletti

Hernan Lopes

Joel Berger

Matt S Trout

Peter Rabbitson

William Lindley

COPYRIGHT AND LICENSE

This program is free software, you can redistribute it and/or modify it underthe terms of the Artistic License version 2.0.

Index

connection

ATTRIBUTES

abstract
auto_migrate
database_class
dsn
max_connections
migrations
options
parent
password
pubsub
search_path
username

METHODS

db
from_string
new

COPYRIGHT AND LICENSE

SEE ALSO

This document was created byman2html,using the manual pages.