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POSharing a Mongoose instance between multiple NPM packages
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copied!<p>In an attempt to modularize a large existing Node+Express+Mongoose application into multiple mountable apps, each developed as a separate NPM package, we're wondering whether sharing a single Mongoose instance between them is a good idea?</p> <p>Let's say we have a suite of NPM packages each containing client-side assets, Mongoose models, and a REST-API implemented with Express. They do share a few common traits but are essentially to be considered separate reusable artefacts. A host application, also Express-based, mounts these under various root URIs:</p> <pre><code>var discussions = require('discussions'), tickets = require('tickets'), events = require('events'), express = require('express'), app = express(); var environment = { ...see below... }; ... app.use('/events-api', events(environment)); app.use('/tickets-api', tickets(environment)); app.use('/discussions-api', discussions(environment)); </code></pre> <p>Now, since the <code>events</code>, <code>tickets</code> and <code>discussions</code> apps (separate NPM packages pulled in via the host <code>package.json</code>) use Mongoose, as do the host application itself, we figured we would pass in the host Mongoose instance through some kind of <code>environment</code> object that also include other stuff that the host wants to share with the mounted apps.</p> <p>Do you see any obvious flaws with this approach? The mounted apps in this case would <strong>not</strong> specify Mongoose as a dependency in their respective <code>package.json</code>, and they would <strong>not</strong> <code>require('mongoose')</code> as normally done but instead get the Mongoose instance from the host which is responsible for connecting it to MongoDB.</p> <p>If this is a bad idea and you suggest each sub-app declare a dependency towards Mongoose on their own, each NPM package would get their own copy of Mongoose and would each have to connect to MongoDB, right?</p> <p>Some background info:</p> <ul> <li>We really do want to include the apps in a host application, running in a single process, rather that having multiple Node instances. The host contains middleware for authentication and other things.</li> <li>We do want to have the apps as separately developed NPM packages included as versioned dependencies of the various host applications that we build, rather than just copying their source to a host application.</li> <li>We realize that reusing the same Mongoose instance between multiple mounted apps will have them share the same model namespace.</li> </ul> <p><strong>Edit:</strong> To clarify the package structure after all has been <code>npm install</code>ed:</p> <pre><code>host/ assets/ models/ routes/ node_modules/ express/ ... mongoose/ ... events/ assets/ ... models/ ... routes/ ... tickets/ assets/ ... models/ ... routes/ ... discussions/ assets/ ... models/ ... routes/ ... </code></pre> <p>That is, the <code>events</code>, <code>tickets</code>, and <code>discussions</code> apps do not include Mongoose (or Express) of their own but are designed to rely on an always-present host application that suppliesd those dependencies.</p> <p>We're assuming here that an NPM package like <code>tickets</code> cannot simply <code>require</code> stuff from the parent, right?</p>

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