text: var async = require('async');
  var Book = require('../models/book');
  var Author = require('../models/author');
  
  // Display list of all Authors
  exports.author_list = function(req, res, next) {
  
      Author.find()
          .sort([['family_name', 'ascending']])
          .exec(function (err, list_authors) {
              if (err) { return next(err); }
              //Successful, so render
              res.render('author_list', { title: 'Author List', author_list:  list_authors});
          });
  
  };
  
  // Display detail page for a specific Author
  exports.author_detail = function(req, res, next) {
  
      async.parallel({
          author: function(callback) {
              Author.findById(req.params.id)
                  .exec(callback);
          },
          authors_books: function(callback) {
              Book.find({ 'author': req.params.id },'title summary')
                  .exec(callback);
          },
      }, function(err, results) {
          if (err) { return next(err); }
          //Successful, so render
  
          res.render('author_detail', { title: 'Author Detail', author: results.author, author_books: results.authors_books } );
      });
  
  };
  
  // Display Author create form on GET
  exports.author_create_get = function(req, res, next) {
      res.render('author_form', { title: 'Create Author'});
  };
  
  // Handle Author create on POST
  exports.author_create_post = function(req, res, next) {
  
      req.checkBody('first_name', 'First name must be specified.').notEmpty(); //We won't force Alphanumeric, because people might have spaces.
      req.checkBody('family_name', 'Family name must be specified.').notEmpty();
      req.checkBody('family_name', 'Family name must be alphanumeric text.').isAlpha();
      req.checkBody('date_of_birth', 'Invalid date').optional({ checkFalsy: true }).isDate();
      req.checkBody('date_of_death', 'Invalid date').optional({ checkFalsy: true }).isDate();
  
      req.sanitize('first_name').escape();
      req.sanitize('family_name').escape();
      req.sanitize('first_name').trim();
      req.sanitize('family_name').trim();
      req.sanitize('date_of_birth').toDate();
      req.sanitize('date_of_death').toDate();
  
      var errors = req.validationErrors();
  
      var author = new Author(
          { first_name: req.body.first_name,
              family_name: req.body.family_name,
              date_of_birth: req.body.date_of_birth,
              date_of_death: req.body.date_of_death
          });
  
      if (errors) {
          res.render('author_form', { title: 'Create Author', author: author, errors: errors});
          return;
      }
      else {
          // Data from form is valid
  
          author.save(function (err) {
              if (err) { return next(err); }
              //successful - redirect to new author record.
              res.redirect(author.url);
          });
      }
  
  };
  
  // Display Author delete form on GET
  exports.author_delete_get = function(req, res, next) {
  
      async.parallel({
          author: function(callback) {
              Author.findById(req.params.id).exec(callback);
          },
          authors_books: function(callback) {
              Book.find({ 'author': req.params.id }).exec(callback);
          },
      }, function(err, results) {
          if (err) { return next(err); }
          //Successful, so render
          res.render('author_delete', { title: 'Delete Author', author: results.author, author_books: results.authors_books } );
      });
  
  };
  
  // Handle Author delete on POST
  exports.author_delete_post = function(req, res, next) {
  
      req.checkBody('authorid', 'Author id must exist').notEmpty();
  
      async.parallel({
          author: function(callback) {
              Author.findById(req.body.authorid).exec(callback);
          },
          authors_books: function(callback) {
              Book.find({ 'author': req.body.authorid },'title summary').exec(callback);
          },
      }, function(err, results) {
          if (err) { return next(err); }
          //Success
          if (results.authors_books>0) {
              //Author has books. Render in same way as for GET route.
              res.render('author_delete', { title: 'Delete Author', author: results.author, author_books: results.authors_books } );
              return;
          }
          else {
              //Author has no books. Delete object and redirect to the list of authors.
              Author.findByIdAndRemove(req.body.authorid, function deleteAuthor(err) {
                  if (err) { return next(err); }
                  //Success - got to author list
                  res.redirect('/catalog/authors');
              });
  
          }
      });
  
  };
  
  // Display Author update form on GET
  exports.author_update_get = function(req, res, next) {
      res.send('NOT IMPLEMENTED: Author update GET' );
  };
  
  // Handle Author update on POST
  exports.author_update_post = function(req, res, next) {
      res.send('NOT IMPLEMENTED: Author update POST' );
  };