Integration

This document is the guidelines for integrating pg-promise with reusable libraries.

standard approach

The standard way is by adding pg-promise as a dependency in your package.json.

advantages:

• isolated use of promise libraries
• coding strictly for the referenced version of pg-promise
• providing your own Initialization Options

disadvantages:

• requires separate database connection parameters
• requires creation of a separate instance of the Database object

If the client module creates its own Database object from the same connection parameters, it will result in a duplicate Database object warning, as explained in the Database API.

via db parameter

You can accept db - Database object as a parameter, to use it directly. And you can access all pg-promise features via property db.$config.

advantages:

• consistent use of the Initialization Options, as configured by the client
• no dependencies: reusing pg-promise and the promise library as configured by the client
• no duplicate Database objects, optimal use of the connection and event listeners

disadvantages:

• cannot set your own Initialization Options, and you can break the client's code, if you try
• can only use the basic promise methods as exposed via db.$config.promise

mixed approach

You can support pg-promise through explicit dependencies (for the default), and via db parameter as a optional override.

This is the recommended approach, because it can suit the needs of both client types:

• clients that use pg-promise internally will be able to pass in db as a parameter
• clients that do not use pg-promise internally will rely on your library's defaults

extras

promises

When using pg-promise via db parameter, you have access to the underlying layer of promises:

• db.$config.promiseLib - the promise library as configured by the client
• db.$config.promise - the basic promise interface as used by pg-promise

If you want to provide compatibility with any promise library configured by pg-promise client, you have to rely on the available basic promise interface:

const $p = db.$config.promise; // your basic promise interface

// for a new promise object:
return $p(function(resolve, reject) {
   // call resolve/reject as needed
});

// for a resolved promise:
return $p.resolve(value);

// for a rejected promise:
return $p.reject(reason);

There are no other methods in the basic promise interface beside the ones shown above.

version

If you want to enforce the minimum-version requirement on the db parameter, you can use the following function:

// Compares a version-parameter to pg-promise database object version,
// and returns the comparison result:
//  -1: database object version is older
//   1: database object version is newer
//   0: the same versions
//
// It will always return -1 for pg-promise prior to 4.4.8,
// starting from which the version could be determined.

const parseVersion = require('vparse');

function comparePGPVersion(db, version) {

    if (!db || !db.constructor || db.constructor.name !== 'Database') {
        throw new TypeError('Parameter \'db\' is invalid.');
    }

    if (!db.$config || !db.$config.version) {
        return -1; // version is prior to 4.4.8
    }

    return parseVersion(db.$config.version).compare(version);
}