pg

What is pg?

The pg npm package is a PostgreSQL client for Node.js. It provides functionalities to connect to a PostgreSQL database server and execute queries, manage transactions, and listen to notifications from the database.

What are pg's main functionalities?

Connecting to a PostgreSQL database

This code sample demonstrates how to connect to a PostgreSQL database using the pg package. It includes creating a new client instance and connecting to the database with a connection string.

const { Client } = require('pg');
const client = new Client({
  connectionString: 'postgresql://user:password@localhost:5432/database'
});
client.connect();

Executing a query

This code sample shows how to execute a SQL query to select all records from a table and print the results. It also handles any potential errors and closes the connection.

client.query('SELECT * FROM my_table', (err, res) => {
  console.log(err ? err.stack : res.rows);
  client.end();
});

Using async/await for queries

This code sample uses async/await syntax to execute a query and print the results. It's a more modern approach to handling asynchronous operations in Node.js.

async function fetchData() {
  const res = await client.query('SELECT * FROM my_table');
  console.log(res.rows);
  client.end();
}
fetchData();

Managing transactions

This code sample illustrates how to manage a transaction with the pg package. It begins a transaction, attempts to insert data, commits the transaction if successful, or rolls back if an error occurs.

async function transactionExample() {
  await client.query('BEGIN');
  try {
    await client.query('INSERT INTO my_table (col) VALUES ($1)', ['data']);
    await client.query('COMMIT');
  } catch (e) {
    await client.query('ROLLBACK');
    throw e;
  }
}
transactionExample();

Listening to notifications

This code sample demonstrates how to listen for notifications from the PostgreSQL server. It sets up an event listener for 'notification' events and executes the LISTEN command to subscribe to a specific notification.

const client = new Client();
client.connect();
client.on('notification', (msg) => {
  console.log('New notification:', msg);
});
client.query('LISTEN my_notification');

Other packages similar to pg

mysql

The mysql package is a client for MySQL databases. It provides similar functionalities to pg, such as connecting to a database, executing queries, and managing transactions. However, it is designed specifically for MySQL and not PostgreSQL.

sequelize

Sequelize is an ORM (Object-Relational Mapping) library for Node.js. It supports multiple database systems, including PostgreSQL. Unlike pg, which is a lower-level client, Sequelize provides a higher-level abstraction with features like model definition, associations, and migrations.

typeorm

TypeORM is another ORM for TypeScript and JavaScript that runs on Node.js. It supports PostgreSQL among other databases. It provides an even higher level of abstraction compared to Sequelize and includes features like data-mapper patterns, repositories, and automatic schema generation.

knex

Knex.js is a SQL query builder for Node.js that supports PostgreSQL, MySQL, SQLite3, and more. It provides chainable query building capabilities and can be used as a query client without the full ORM features. It's a middle ground between pg and full ORMs like Sequelize and TypeORM.

README

#node-postgres

Non-blocking PostgreSQL client for node.js. Pure JavaScript and native libpq bindings. Active development, well tested, and production use.

Installation

npm install pg

Examples

Simple, using built-in client pool

var pg = require('pg'); 
//or native libpq bindings
//var pg = require('pg').native

var conString = "tcp://postgres:1234@localhost/postgres";

//error handling omitted
pg.connect(conString, function(err, client) {
  client.query("SELECT NOW() as when", function(err, result) {
    console.log("Row count: %d",result.rows.length);  // 1
    console.log("Current year: %d", result.rows[0].when.getYear());
  });
});

Evented api

var pg = require('pg'); //native libpq bindings = `var pg = require('pg').native`
var conString = "tcp://postgres:1234@localhost/postgres";

var client = new pg.Client(conString);
client.connect();

//queries are queued and executed one after another once the connection becomes available
client.query("CREATE TEMP TABLE beatles(name varchar(10), height integer, birthday timestamptz)");
client.query("INSERT INTO beatles(name, height, birthday) values($1, $2, $3)", ['Ringo', 67, new Date(1945, 11, 2)]);
client.query("INSERT INTO beatles(name, height, birthday) values($1, $2, $3)", ['John', 68, new Date(1944, 10, 13)]);

//queries can be executed either via text/parameter values passed as individual arguments
//or by passing an options object containing text, (optional) parameter values, and (optional) query name
client.query({
  name: 'insert beatle',
  text: "INSERT INTO beatles(name, height, birthday) values($1, $2, $3)",
  values: ['George', 70, new Date(1946, 02, 14)]
});

//subsequent queries with the same name will be executed without re-parsing the query plan by postgres
client.query({
  name: 'insert beatle',
  values: ['Paul', 63, new Date(1945, 04, 03)]
});
var query = client.query("SELECT * FROM beatles WHERE name = $1", ['John']);

//can stream row results back 1 at a time
query.on('row', function(row) {
  console.log(row);
  console.log("Beatle name: %s", row.name); //Beatle name: John
  console.log("Beatle birth year: %d", row.birthday.getYear()); //dates are returned as javascript dates
  console.log("Beatle height: %d' %d\"", Math.floor(row.height/12), row.height%12); //integers are returned as javascript ints
});

//fired after last row is emitted
query.on('end', function() { 
  client.end();
});

Example notes

node-postgres supports both an 'event emitter' style API and a 'callback' style. The callback style is more concise and generally preferred, but the evented API can come in handy. They can be mixed and matched. The only events which do not fire when callbacks are supplied are the error events, as they are to be handled by the callback function.

All examples will work with the pure javascript bindings (currently default) or the libpq native (c/c++) bindings (currently in beta)

To use native libpq bindings replace require('pg') with require('pg').native.

The two share the same interface so no other code changes should be required. If you find yourself having to change code other than the require statement when switching from pg to pg.native, please report an issue.

Info

• pure javascript client and native libpq bindings share the same api
• heavily tested
  • the same suite of 200+ integration tests passed by both javascript & libpq bindings
  • benchmark & long-running memory leak tests performed before releases
  • tested with with
    • postgres 8.x, 9.x
    • Linux, OS X
    • node 2.x & 4.x
• row-by-row result streaming
• built-in (optional) connection pooling
• responsive project maintainer
• supported PostgreSQL features
  • parameterized queries
  • named statements with query plan caching
  • async notifications
  • extensible js<->postgresql data-type coercion
• query queue
• active development
• fast
• close mirror of the node-mysql api for future multi-database-supported ORM implementation ease

Contributors

Many thanks to the following:

• creationix
• felixge
• pshc
• pjornblomqvist
• JulianBirch
• ef4
• napa3um
• drdaeman
• booo
• neonstalwart

Documentation

Documentation is a work in progress primarily taking place on the github WIKI

Documentation

PLEASE check out the WIKI

If you have a question, post it to the FAQ section of the WIKI so everyone can read the answer

Production Use

• bayt.com

if you use node-postgres in production and would like your site listed here, fork & add it

Help

If you need help or run into any issues getting node-postgres to work on your system please report a bug or contact me directly. I am usually available via google-talk at my github account public email address.

License

Copyright (c) 2010 Brian Carlson ([e-mail])

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.