Mongoose models scheme in separate modul

Question

Disclaimer: I am new to mongoose/node, so please excuse me if I am misunderstanding some basic things. Yes, I found already a few postings about this topic, but could not adapt it to my needs.

I structured my main-project into multiple separate projects. One separation is the "app-core" project, which will contain the core-models and -modules, to be injected by each other project (app-core is configured as dependency in the package.json file of each project).

A (simplified) model within the app-core currently looks like this:

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var IndustrySchema = new Schema({
name: {
    type: String,
    required: true
}
}); 

module.exports = mongoose.model('Industry', IndustrySchema);

The wep-app includes this model as follow:

var Industry = require('app-core/models/Industry');

and creates the MongoDB connection like this:

var DB_URL = 'mongodb://localhost/hellowins';
var mongoose = require('mongoose');
var mongooseClient = mongoose.connect(DB_URL);
mongooseClient.connection.on('connected',function () {
  console.log("MongoDB is connected");
});

Now I have the problem, that the model will not use the mongo connection that is defined in the app-web project, rather it will consider the connection configured in the app-core.

Due to encapsulation and responsibility design I definitly don't want the core to define the connections for each possible app (which may include the core-app). So somehow I need to specify the the scheme only in the core.

I read already that I should not require the model itself (/app-core/models/Industry), and use the mongoose model instead

var Industry = mongoose.model("Industry");

But then I get the error

MissingSchemaError: Schema hasn't been registered for model "Test"

To fix this, I should register the models manually, like adviced in the first link (at the top of my posting). But somehow I don't like this approach, because I'd need to extend this everytime the application uses a new model.

And further I need a mongo connection even in the core-app - at least to run the mocha tests.

So I am bit confused about how to structure the architecture in this case.

UPDATE #1

I found now one working solution. But, unfortunately, this does not fit my requirements completely, because it is pretty difficult (resp. ugly) to extend a model by hooks (ie TestSchema.pre('save'..)).

Model (app-core)

exports.model = {
    name: {
        type: String,
        required: true
    }
};

models.js (app-web, executed once on startup)

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var models = ['Test']; // add many
exports.initialize = function() {
    var l = models.length;
    for (var i = 0; i < l; i++) {
        var model = require('hw-core/models/' + models[i]);
        var ModelSchema = new Schema(model.model);
        module.exports = mongoose.model(models[i], ModelSchema);
}

};

app.js (web-app)

require('./conf/app_models.js').initialize();

Then I just can get a model as follow

var mongoose = require('mongoose');
var TestModel = mongoose.model("Test");
var Test = new TestModel();

Answer 1

Why don't you try to export the mongoose instance from your app-core module and use it later in the web-app to connect to a database

app-core index.js

var mongoose = require('mongoose');
module.exports = {
    mongooseInstance: mongoose };

web-app index.js

var core = require('app-core'),
    mongoose = core.mongooseInstance,

mongooseClient = mongoose.connect(DB_URL);
// and so on

This might work as long as you require your models in your controllers which are initialized after the code from the index.js. I hope my response is helpful.