gistfile1.js

// Page is the returned mongoose Model for 'Page'
Page
  // finding all pages that have isPublished set to true
  .find({isPublished: true})
  // populating the sub-documents 'album' from the 'Album' Model
  .populate({
    path: 'album'
  })
  // execute the query
  .exec(function (error, pages) {
    // if it errors just return right out of there
    if (error) return callback(error);
    // else callback node style (first value error (which is null), second value the result)
    // filter the pages to only the ones we need
    callback(null, pages.filter(function (page) {
      // filter accepts 'true' for anything you want to keep and 'false' for not
      // if there's no album then return false (reject)
      // if the album has a url of 'shop' or 'events' then return true (keep)
      // otherwise return false (reject)
      return !page.album ?
        false :
        page.album.url === 'shop' || page.album.url === 'events';
    }));
  });