Attaches a function called "seed" to Mongoose models, which basically wraps the create function, but returns a promise. This way seeding can be done through a promise chain.

gistfile1.js

var mongoose = require('mongoose');
mongoose.Model.seed = function(entities) {
    var promise = new mongoose.Promise;
    this.create(entities, function(err) {
        if(err) { promise.reject(err); }
        else    { promise.resolve(); }
    });
    return promise;
};