where(query) {
    return this._findRecordsWhere(query).map(duplicate);
  }
Returns an array of models from `collection` that match the
    key-value pairs in the `query` object. Note that a string
    comparison is used. `query` is a POJO.

    ```js
    // Given users = [ { id: 1, name: 'Link' }, { id: 2, name: 'Zelda' } ]

    db.users.where({ name: 'Zelda' }); // [ { id: 2, name: 'Zelda' } ]
    ```

    @method where
    @param query
    @public