pg-promise

What is pg-promise?

pg-promise is a Node.js library for interfacing with PostgreSQL databases. It provides a powerful and flexible API for executing SQL queries, managing transactions, and handling connections. The library is built on top of the 'pg' module and adds a layer of promise-based functionality, making it easier to work with asynchronous operations.

What are pg-promise's main functionalities?

Basic Query Execution

This feature allows you to execute basic SQL queries. The example demonstrates how to select all active users from a 'users' table.

const pgp = require('pg-promise')();
const db = pgp('postgres://username:password@host:port/database');

db.any('SELECT * FROM users WHERE active = $1', [true])
  .then(data => {
    console.log(data);
  })
  .catch(error => {
    console.error(error);
  });

Parameterized Queries

This feature allows you to use parameterized queries to prevent SQL injection. The example shows how to insert a new user into the 'users' table and return the new user's ID.

const pgp = require('pg-promise')();
const db = pgp('postgres://username:password@host:port/database');

const query = 'INSERT INTO users(name, email) VALUES($1, $2) RETURNING id';
const values = ['John Doe', '[e-mail]'];

db.one(query, values)
  .then(data => {
    console.log('New User ID:', data.id);
  })
  .catch(error => {
    console.error(error);
  });

Transactions

This feature allows you to manage transactions, ensuring that a series of queries either all succeed or all fail. The example demonstrates how to insert a user and their profile in a single transaction.

const pgp = require('pg-promise')();
const db = pgp('postgres://username:password@host:port/database');

db.tx(t => {
  return t.batch([
    t.none('INSERT INTO users(name, email) VALUES($1, $2)', ['John Doe', '[e-mail]']),
    t.none('INSERT INTO profiles(user_id, bio) VALUES((SELECT id FROM users WHERE email = $1), $2)', ['[e-mail]', 'Bio for John Doe'])
  ]);
})
  .then(data => {
    console.log('Transaction successful');
  })
  .catch(error => {
    console.error('Transaction failed:', error);
  });

Connection Management

This feature allows you to manage database connections explicitly. The example shows how to establish and release a connection.

const pgp = require('pg-promise')();
const db = pgp('postgres://username:password@host:port/database');

db.connect()
  .then(obj => {
    obj.done(); // success, release the connection;
    console.log('Connection successful');
  })
  .catch(error => {
    console.error('Connection failed:', error);
  });

Other packages similar to pg-promise

pg

The 'pg' package is a low-level PostgreSQL client for Node.js. It provides basic functionality for connecting to a PostgreSQL database and executing queries. Unlike pg-promise, it does not include built-in promise support, so you need to handle asynchronous operations manually or use a promise library.

sequelize

Sequelize is an ORM (Object-Relational Mapper) for Node.js that supports multiple SQL dialects, including PostgreSQL. It provides a higher-level API for defining models and relationships, making it easier to work with complex data structures. Unlike pg-promise, which is focused on SQL query execution, Sequelize abstracts much of the SQL away.

knex

Knex.js is a SQL query builder for Node.js that supports multiple database types, including PostgreSQL. It provides a flexible and chainable API for building SQL queries programmatically. While pg-promise focuses on executing raw SQL queries, Knex.js allows you to construct queries using JavaScript methods.

README

Introduction

This library joins Promise and PG to help writing easy-to-read database code that relies on promises:

• Streamlined database code structure, thanks to full Promise integration;
• Robust, declarative approach to handling results from every single query;
• Database connections are managed automatically in every usage case;
• Functions, Procedures and Transactions are all fully supported.

Install

$ npm install pg-promise

Getting started

1. Load the library

var pgpLib = require('pg-promise');

2. Configure database connection

Use one of the two ways to specify connection:

• Configuration object:

var cn = {
    host: 'localhost', // server name or ip address
    port: 5432,
    database: 'my_db_name',
    user: 'user_name',
    password: 'user_password'
};

• Connection string:

var cn = "postgres://username:password@host:port/database";

This library doesn't use any of the connection's details, it simply passes them on to PG when opening a new connection. For more details see ConnectionParameters class in PG, such as additional connection properties supported.

3. Initialize the library

var pgp = pgpLib(cn);

NOTE: Only one global instance should be used throughout the application.

See also chapter Advanced for the use of parameter options during initialization. But for now you are ready to use the library.

Usage

The basics

In order to eliminate the chances of unexpected query results and make code more robust, each request is parametrized with the expected/supported Query Result Mask, using type queryResult as shown below:

queryResult = {
    one: 1,     // single-row result is expected;
    many: 2,    // multi-row result is expected;
    none: 4     // no rows expected.
};

In the following generic-query example we indicate that the call can return any number of rows:

pgp.query("select * from users", queryResult.none | queryResult.many);

which is equivalent to calling:

pgp.manyOrNone("select * from users");

This usage pattern is facilitated through result-specific methods that can be used instead of the generic query:

pgp.many("select * from users"); // one or more records are expected
pgp.one("select * from users limit 1"); // one record is expected
pgp.none("update users set active=TRUE where id=1"); // no records expected

The mixed-result methods are:

• oneOrNone - expects 1 or 0 rows to be returned;
• manyOrNone - any number of rows can be returned, including 0.

Each of the query calls returns a Promise object, as shown below, to be used in the standard way. And when the expected and actual results do not match, the call will be rejected.

pgp.many("select * from users").then(function(data){
    console.log(data); // printing the data received
},function(reason){
    console.log(reason); // printing the reason why the call was rejected
});

Functions and Procedures

In PostgreSQL stored procedures are just functions that usually do not return anything.

Suppose we want to call a function to find audit records by user id and maximum timestamp. We can make the call as shown below:

pgp.func('findAudit', [
    123,
    new Date()
]);

We passed it user id = 123, plus current Date/Time as the timestamp. We assume that the function signature matches the parameters that we passed. All values passed are serialized automatically to comply with PostgreSQL type formats.

And when you are not expecting any return results, call pgp.proc instead. Both methods return a Promise object.

Transactions

Every call shown in chapters above would acquire a new connection from the pool and release it when done. In order to execute a transaction on the same connection, a transaction class is to be used.

Example:

var promise = require('promise');

var tx = new pgp.tx(); // creating a new transaction object

tx.exec(function(/*client*/){

    // creating sequence of transaction queries:
    var query1 = tx.none("update users set active=TRUE where id=123");
    var query2 = tx.one("insert into audit(entity, id) values('users', 123) returning id");

    // returning a promise that determines a successful transaction:
    return promise.all([query1, query2]); // all of the queries are to be resolved;

}).then(function(data){
    console.log(data); // printing successful transaction output
}, function(reason){
    console.log(reason); // printing the reason why the transaction failed
});

In the example above we create a new transaction object and call its method exec, passing it a call-back function that must do all the queries needed and return a Promise object. In the example we use promise.all to indicate that we want both queries inside the transaction to resolve before executing a COMMIT. And if one of the queries fails to resolve, ROLLBACK will be executed instead, and the transaction call will be rejected.

Notes

• While inside a transaction, we make calls to the same-named methods as outside of transactions, except we do it on the transaction object instance now, as opposed to the global pgp object, which gives us access to the shared connection object. The same goes for calling functions and procedures within transactions, using tx.func and tx.proc accordingly.
• Just for flexibility, the transaction call-back function takes parameter client - the connection object.

Type Helpers

The library provides several helper functions to convert basic javascript types into their proper PostgreSQL presentation that can be passed directly into queries or functions as parameters. All of such helper functions are located within namespace pgp.as:

pgp.as.bool(value); // returns proper PostgreSQL boolean presentation

pgp.as.text(value); // returns proper PostgreSQL text presentation,
                    // fixing single-quote symbols, wrapped in quotes

pgp.as.date(value); // returns proper PostgreSQL date/time presentation,
                    // wrapped in quotes.

As these helpers are not associated with a connection, and thus can be called from anywhere.

Advanced

Initialization options

Initialization options are supported as shown in the example:

var options = {
    connect: function(client){
        var cp = client.connectionParameters;
        console.log("Connected to database '" + cp.database + "'");
    },
    disconnect: function(client){
        var cp = client.connectionParameters;
        console.log("Disconnected from database '" + cp.database + "'");
    }
};
var pgp = pgpLib(cn, options);

Two events supported at the moment - connect and disconnect, to notify of virtual connections being established or released accordingly. Each event takes parameter client, which is the client connection object. These events are mostly for connection monitoring, while debugging your application.

De-initialization

When exiting your application, make the following call:

pgp.end();

This will release pg connection pool globally and make sure that the process terminates without delay. If you do not call it, your process may be waiting for 30 seconds (default) or so, waiting for the pg connection pool to expire.

Direct connection usage

The library exposes method connect in case of some unique reason that you may want to manage the connection yourself, as opposed to trusting the library doing it for you automatically.

Usage example:

pgp.connect().then(function(db){
    // connection was established successfully;

    // do stuff with the connection object (db.client) and/or queries;

    // when done with all the queries, call done():
    db.done();

}, function(reason){
    // failed to connect;
    console.log('Connection problem: ' + reason);
});

NOTE: When using the direct connection, events connect and disconnect won't be fired.

History

• A refined version 0.1.4 released on March 5th, 2015.
• First solid Beta, 0.1.2 on March 4th, 2015.
• It reached first Beta version 0.1.0 on March 4th, 2015.
• The first draft v0.0.1 was published on March 3rd, 2015, and then rapidly incremented due to many initial changes that had to come in, mostly documentation.

License

Copyright (c) 2014-2015 Vitaly Tomilov ([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.