Опитайте-
mongoose.model('category', CategorySchema, 'categories');
mongoose.model('topics', TopicSchema, 'categories');
mongoose.model('articles', ArticlesSchema, 'categories');
Както е споменато в документите:http://mongoosejs.com/docs/api.html# index_Mongoose-model
Вижте - https://stackoverflow.com/a/14454102/3896066