gistfile1.js

var mongoose = require('mongoose'),
    auto_increment = require('mongoose-auto-increment');

var category_schema = new mongoose.Schema({
  name: {required: true, type: String},
  categories: [{ name: {required: true, type: String}}],
  parent_id: Number
});

category_schema.plugin(auto_increment.plugin, 'Category');
category_schema.plugin(auto_increment.plugin, 'Category.categories');

var Category = module.exports = mongoose.model('Category', category_schema);