*  There is no exposed reference from the model to bookshelf (e.g. can't do something like `Ad.Bookshelf.knex`). Need to require the bookshelf instance itself.

### Getting count of models matching certain criteria
```js
// select count(*) from "ads" where "classified_id" = 2'
Ad.where({ classified_id: 2 })
  .query() // <- returns QueryBuild instance
  .count()
  .then(function (count) {
    console.log('\n***', count);
  });
```