NoSQL App

A blog server backed by MongoDB and driven by a Python client. One class, MongoBlogServer, maps four text commands — post, show, comment, and delete — onto operations against a single collection.

Everything lives in database blog, collection posts, where both posts and comments are documents in that one collection. A post carries blogName, userName, title, postBody, a tags array, a timestamp, a permalink, and a comments array. The permalink is derived, not supplied: a post's is its blog name joined to its title with every non-alphanumeric run replaced by an underscore, and a comment's is its timestamp. A unique index on permalink enforces that each is distinct, and a second index on blogName turns "show this blog" into a keyed lookup rather than a scan of the collection.

Comments are stored as references rather than embedded. A comment is its own document in the same posts collection; the parent's comments array holds only the permalink strings of its children. A thread is therefore a tree linked by permalink: show_posts finds a blog's posts, then walks each comments array with a find_one by permalink, recursing into nested replies. That is adjacency-by-reference in a store with no joins — the relationship the application maintains, because MongoDB does not.

Each command is a short sequence of collection operations. post inserts a document; comment inserts a comment document and then $pushes its permalink into the parent with an update_one; delete is a soft delete that $sets postBody to "deleted by <user>" rather than removing the document, so replies that still reference it stay reachable.

The index behind those keyed lookups is a B-tree — the same balanced tree relational engines reach for.

Collaborative project with Ke Lou.