MongoDB & Node.js Final 4 - Enhancing the Blog to support viewers liking certain comments In this problem, you will be enhancing the blog project to support users liking certain comments and the like counts showing up the in the permalink page. Start by downloading the code in Final4.zip and loading up the blog dataset posts.json. The user inter…

final4-js

/* The PostsDAO must be constructed with a connected database object */
function PostsDAO(db) {
    "use strict";

    /* If this constructor is called without the "new" operator, "this" points
     * to the global object. Log a warning and call it correctly. */
    if (false === (this instanceof PostsDAO)) {
        console.log('Warning: PostsDAO constructor called without "new" operator');
        return new PostsDAO(db);
    }

    var posts = db.collection("posts");

    this.insertEntry = function (title, body, tags, author, callback) {
        "use strict";
        console.log("inserting blog entry" + title + body);

        // fix up the permalink to not include whitespace
        var permalink = title.replace( /\s/g, '_' );
        permalink = permalink.replace( /\W/g, '' );

        // Build a new post
        var post = {"title": title,
                "author": author,
                "body": body,
                "permalink":permalink,
                "tags": tags,
                "comments": [],
                "date": new Date()}

        // now insert the post
        posts.insert(post, function (err, result) {
            "use strict";

            if (err) return callback(err, null);

            console.log("Inserted new post");
            callback(err, permalink);
        });
    }

    this.getPosts = function(num, callback) {
        "use strict";

        posts.find().sort('date', -1).limit(num).toArray(function(err, items) {
            "use strict";

            if (err) return callback(err, null);

            console.log("Found " + items.length + " posts");

            callback(err, items);
        });
    }

    this.getPostsByTag = function(tag, num, callback) {
        "use strict";

        posts.find({ tags : tag }).sort('date', -1).limit(num).toArray(function(err, items) {
            "use strict";

            if (err) return callback(err, null);

            console.log("Found " + items.length + " posts");

            callback(err, items);
        });
    }

    this.getPostByPermalink = function(permalink, callback) {
        "use strict";
        posts.findOne({'permalink': permalink}, function(err, post) {
            "use strict";

            if (err) return callback(err, null);

            // XXX: Look here for final exam to see where we store "num_likes"

            // fix up likes values. set to zero if data is not present
            if (typeof post.comments === 'undefined') {
                post.comments = [];
            }

            // Each comment document in a post should have a "num_likes" entry, so we have to
            // iterate all the comments in the post to make sure that is the case
            for (var i = 0; i < post.comments.length; i++) {
                if (typeof post.comments[i].num_likes === 'undefined') {
                    post.comments[i].num_likes = 0;
                }
                post.comments[i].comment_ordinal = i;
            }
            callback(err, post);
        });
    }

    this.addComment = function(permalink, name, email, body, callback) {
        "use strict";

        var comment = {'author': name, 'body': body}

        if (email != "") {
            comment['email'] = email
        }

        posts.update({'permalink': permalink}, {'$push': {'comments': comment}}, function(err, numModified) {
            "use strict";

            if (err) return callback(err, null);

            callback(err, numModified);
        });
    }

    this.incrementLikes = function(permalink, comment_ordinal, callback) {
        "use strict";

        // The "comment_ordinal" argument specifies which comment in the post we are looking at
        // Here is an example of how to build a selector with the 'comment_ordinal' variable
        // We have to do it this way because a literal object with variables in field names such as:
        // { 'comments.' + comment_ordinal + '.author' : 'Frank' } is illegal Javascript.
        var selector_example = {};
        var comment_ordinal_example = 0;
        selector_example['comments.' + comment_ordinal_example + '.author'] = 'Frank';
        // Now selector_example = { 'comments.0.author' : 'Frank' } which is a selector for the
        // string 'Frank' in the 'author' field of the first element of the 'comments' array (which
        // is zero indexed).

        var selector = {};
        selector['comments.' + comment_ordinal + '.num_likes'] = 1;

        // TODO: Final exam question - Increment the number of likes
        posts.update({'permalink': permalink}, {$inc: selector}, function(err, numModified) {
            if (err)
                return callback(err, null);
            else
                callback(err, numModified);
        });
        // callback(Error("incrementLikes NYI"), null);
    }
}

module.exports.PostsDAO = PostsDAO;