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Cover image for Mongoose calls examples with async-await in an ExpressJS API
Adrian Matei
Adrian Matei

Posted on • Edited on • Originally published at codepedia.org

Mongoose calls examples with async-await in an ExpressJS API

#node #javascript #mongoose #mongodb

A lot has been written already about the transition from callbacks
to promises and now to the new async/await1 feature in ES7.

"The purpose of async/await functions is to simplify the behavior of using promises synchronously and to perform some behavior on a group of Promises. Just as Promises are similar to structured callbacks, async/await is similar to combining generators and promises."1

In this blog post I present what this code "upgrade" meant for CRUD operations performed on dev bookmarks. I use Moongoose in an ExpressJS/NodeJS backend to perform the operations against a MongoDB database. The source code is available on Github.

In a later refactoring the database access part has been decoupled from ExpressJS and moved to separate service functions. Thanks to unified error handling the database errors are now handled centrally.

Create

Before 

router.post('/:id/bookmarks', keycloak.protect(), function(req, res, next){
  const descriptionHtml = req.body.descriptionHtml ? req.body.descriptionHtml: converter.makeHtml(req.body.description);

  console.log(req.body);

  var bookmark = new Bookmark({
    name: req.body.name,
    location: req.body.location,
    language: req.body.language,
    description: req.body.description,
    descriptionHtml: descriptionHtml,
    category: req.body.category,
    tags: req.body.tags,
    publishedOn: req.body.publishedOn,
    githubURL: req.body.githubURL,
    userId: req.params.id,
    shared: req.body.shared,
    starredBy: req.body.starredBy
  });

  console.log('Bookmark to create ' + bookmark);

  bookmark.save(function (err, updatedBookmark) {
    if (err){

      if(err.name == 'ValidationError'){
        var errorMessages = [];
        for (var i in err.errors) {
          errorMessages.push(err.errors[i].message);
        }

        var error = new Error('Validation MyError', errorMessages);
        console.log(JSON.stringify(error));
        res.setHeader('Content-Type', 'application/json');
        return res.status(409).send(JSON.stringify(new MyError('Validation Error', errorMessages)));
      }

      console.log(err);
      res.status(500).send(err);
    } else {
      res.set('Location', 'http://localhost:3000/' + req.params.id + '/bookmarks/' + updatedBookmark.id);
      res.status(201).send({response:'Bookmark created for userId ' + req.params.id});
    }
    // saved!
  });

});
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After

Router 

personalBookmarksRouter.post('/', keycloak.protect(), async (request, response) => {

  UserIdValidator.validateUserId(request);
  const bookmark = bookmarkHelper.buildBookmarkFromRequest(request);
  let newBookmark = await PersonalBookmarksService.createBookmark(request.params.userId, bookmark);

  response
    .set('Location', `${config.basicApiUrl}private/${request.params.userId}/bookmarks/${newBookmark.id}`)
    .status(HttpStatus.CREATED)
    .send({response: 'Bookmark created for userId ' + request.params.userId});

});
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Service 

let createBookmark = async function (userId, bookmark) {
  BookmarkInputValidator.validateBookmarkInput(userId, bookmark);

  await BookmarkInputValidator.verifyPublicBookmarkExistenceOnCreation(bookmark);

  let newBookmark = await bookmark.save();

  return newBookmark;
}
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Read

Before 

/* GET bookmarks for user */
router.get('/:userId/bookmarks/:bookmarkId', keycloak.protect(), function(req, res, next) {
    Bookmark.findOne({_id: bookmarkId, userId:req.params.userId}, function(err, bookmark){
      if(err){
        return res.status(500).send(err);
      }
      res.send(bookmark);
    });
});
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After

Router 

/* GET bookmarks for user */
personalBookmarksRouter.get('/:bookmarkId', keycloak.protect(), async (request, response) => {
  UserIdValidator.validateUserId(request);

  const {userId, bookmarkId} = request.params;
  const bookmark = await PersonalBookmarksService.getBookmarkById(userId, bookmarkId);

  return response.status(HttpStatus.OK).send(bookmark);
});
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Service 

let getBookmarkById = async (userId, bookmarkId) => {
  const bookmark = await Bookmark.findOne({
    _id: bookmarkId,
    userId: userId
  });

  if (!bookmark) {
    throw new NotFoundError(`Bookmark NOT_FOUND the userId: ${userId} AND id: ${bookmarkId}`);
  } else {
    return bookmark;
  }
};
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Update

Before 

/**
 * full UPDATE via PUT - that is the whole document is required and will be updated
 * the descriptionHtml parameter is only set in backend, if only does not come front-end (might be an API call)
 */
router.put('/:userId/bookmarks/:bookmarkId', keycloak.protect(), function(req, res, next) {
  if(!req.body.descriptionHtml){
    req.body.descriptionHtml = converter.makeHtml(req.body.description);
  }
  Bookmark.findOneAndUpdate({_id: req.params.bookmarkId, userId: req.params.userId}, req.body, {new: true}, function(err, bookmark){
    if(err){
      if (err.name === 'MongoError' && err.code === 11000) {
        res.status(409).send(new MyError('Duplicate key', [err.message]));
      }

      res.status(500).send(new MyError('Unknown Server Error', ['Unknow server error when updating bookmark for user id ' + req.params.userId + ' and bookmark id '+ req.params.bookmarkId]));
    }
    if(!bookmark){
      return res.status(404).send('Bookmark not found for user');
    }
    res.status(200).send(bookmark);
  });

});
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After

Router 

/**
 * full UPDATE via PUT - that is the whole document is required and will be updated
 * the descriptionHtml parameter is only set in backend, if only does not come front-end (might be an API call)
 */
personalBookmarksRouter.put('/:bookmarkId', keycloak.protect(), async (request, response) => {

  UserIdValidator.validateIsAdminOrUserId(request);

  const bookmark = bookmarkHelper.buildBookmarkFromRequest(request);

  const {userId, bookmarkId} = request.params;
  const updatedBookmark = await PersonalBookmarksService.updateBookmark(userId, bookmarkId, bookmark);

  return response.status(HttpStatus.OK).send(updatedBookmark);
});
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Service 

let updateBookmark = async (userId, bookmarkId, bookmark) => {

  BookmarkInputValidator.validateBookmarkInput(userId, bookmark);

  await BookmarkInputValidator.verifyPublicBookmarkExistenceOnUpdate(bookmark, userId);

  const updatedBookmark = await Bookmark.findOneAndUpdate(
    {
      _id: bookmarkId,
      userId: userId
    },
    bookmark,
    {new: true}
  );

  const bookmarkNotFound = !updatedBookmark;
  if (bookmarkNotFound) {
    throw new NotFoundError('Bookmark NOT_FOUND with id: ' + bookmarkId + ' AND location: ' + bookmark.location);
  } else {
    return updatedBookmark;
  }
};
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Delete

Before 

/*
* DELETE bookmark for user
*/
router.delete('/:userId/bookmarks/:bookmarkId', keycloak.protect(), function(req, res, next) {
  Bookmark.findOneAndRemove({_id: req.params.bookmarkId, userId: req.params.userId}, function(err, bookmark){
    if(err){
      return res.status(500).send(new MyError('Unknown server error', ['Unknown server error when trying to delete bookmark with id ' + req.params.bookmarkId]));
    }
    if(!bookmark){
      return res.status(404).send(new MyError('Not Found Error', ['Bookmark for user id ' + req.params.userId + ' and bookmark id '+ req.params.bookmarkId + ' not found']));
    }
    res.status(204).send('Bookmark successfully deleted');
  });

});
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After

Router 

/*
* DELETE bookmark for user
*/
personalBookmarksRouter.delete('/:bookmarkId', keycloak.protect(), async (request, response) => {

  UserIdValidator.validateIsAdminOrUserId(request);

  await PersonalBookmarksService.deleteBookmarkById(request.params.userId, request.params.bookmarkId);
  return response.status(HttpStatus.NO_CONTENT).send();
});
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Service 

let deleteBookmarkById = async (userId, bookmarkId) => {
  const bookmark = await Bookmark.findOneAndRemove({
    _id: bookmarkId,
    userId: userId
  });

  if (!bookmark) {
    throw new NotFoundError('Bookmark NOT_FOUND with id: ' + bookmarkId);
  }

  return true;
};
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Unified error handling

As mentioned in the beginning of the post the error handling has been centralised - see below the code snippet dealing
with MongoDB Errors:


app.use(function handleDatabaseError(error, request, response, next) {
  if (error instanceof MongoError) {
    if (error.code === 11000) {
      return response
        .status(HttpStatus.CONFLICT)
        .json({
          httpStatus: HttpStatus.CONFLICT,
          type: 'MongoError',
          message: error.message
        });
    } else {
      return response.status(503).json({
        httpStatus: HttpStatus.SERVICE_UNAVAILABLE,
        type: 'MongoError',
        message: error.message
      });
    }
  }
  next(error);
});
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Conclusion

Note how the code has become shorter, easier to read (especially for someone like me, with a Java/JavaEE background) and the error handling is now much clearer.

Another cool feature of async/await is how to easily implement multiple parallel, but that in a coming post...

This post was originally published at Cleaner code in NodeJs with async-await - Mongoose calls example

  1. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function ↩

Top comments (1)

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arghanilanjonnondi profile image
Argha-Nilanjon-Nondi •

Thanks for simplifying mongoose

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