text: var Genre = require('../models/genre');
  var Book = require('../models/book');
  var async = require('async');
  const validator = require('express-validator');
  
  // Display list of all Genre.
  exports.genre_list = function(req, res) {
      Genre.find()
      .populate('genre')
      .sort([['name', 'ascending']])
      .exec(function (err, list_genre) {
        if (err) { return next(err); }
        //Successful, so render
        res.render('genre_list', { title: 'Genre List', genre_list: list_genre });
      });
  };
  
  // Display detail page for a specific Genre.
  exports.genre_detail = function(req, res, next) {
  
      async.parallel({
          genre: function(callback) {
              Genre.findById(req.params.id)
                .exec(callback);
          },
  
          genre_books: function(callback) {
              Book.find({ 'genre': req.params.id })
                .exec(callback);
          },
  
      }, function(err, results) {
          if (err) { return next(err); }
          if (results.genre==null) { // No results.
              var err = new Error('Genre not found');
              err.status = 404;
              return next(err);
          }
          // Successful, so render
          res.render('genre_detail', { title: 'Genre Detail', genre: results.genre, genre_books: results.genre_books } );
      });
  
  };
  
  
  // Display Genre create form on GET.
  exports.genre_create_get = function(req, res, next) {     
      res.render('genre_form', { title: 'Create Genre' });
    };
  
  // Handle Genre create on POST.
  exports.genre_create_post =  [
     
      // Validate that the name field is not empty.
      validator.body('name', 'Genre name required').trim().isLength({ min: 1 }),
      
      // Sanitize (escape) the name field.
      validator.sanitizeBody('name').escape(),
    
      // Process request after validation and sanitization.
      (req, res, next) => {
    
        // Extract the validation errors from a request.
        const errors = validator.validationResult(req);
    
        // Create a genre object with escaped and trimmed data.
        var genre = new Genre(
          { name: req.body.name }
        );
    
    
        if (!errors.isEmpty()) {
          // There are errors. Render the form again with sanitized values/error messages.
          res.render('genre_form', { title: 'Create Genre', genre: genre, errors: errors.array()});
          return;
        }
        else {
          // Data from form is valid.
          // Check if Genre with same name already exists.
          Genre.findOne({ 'name': req.body.name })
            .exec( function(err, found_genre) {
               if (err) { return next(err); }
    
               if (found_genre) {
                 // Genre exists, redirect to its detail page.
                 res.redirect(found_genre.url);
               }
               else {
    
                 genre.save(function (err) {
                   if (err) { return next(err); }
                   // Genre saved. Redirect to genre detail page.
                   res.redirect(genre.url);
                 });
    
               }
    
             });
        }
      }
    ];
  
  
  
  // Display Genre delete form on GET.
  exports.genre_delete_get = function(req, res) {
      res.send('NOT IMPLEMENTED: Genre delete GET');
  };
  
  // Handle Genre delete on POST.
  exports.genre_delete_post = function(req, res) {
      res.send('NOT IMPLEMENTED: Genre delete POST');
  };
  
  // Display Genre update form on GET.
  exports.genre_update_get = function(req, res) {
      res.send('NOT IMPLEMENTED: Genre update GET');
  };
  
  // Handle Genre update on POST.
  exports.genre_update_post = function(req, res) {
      res.send('NOT IMPLEMENTED: Genre update POST');
  };