Data Model (Conceptual)

This section describes the conceptual data model. Field names, data types, and implementation details are intentionally simplified and do not reflect the private source code.

Entity-Relationship Diagram

Entity descriptions

User

Represents an application account and its public profile.

Field	Purpose
`id`	Unique identifier
`username`	Unique display name
`email`	Login credential (unique)
`passwordHash`	Bcrypt-hashed password (never returned in API responses)
`bio`	Optional short biography
`avatarUrl`	Reference to profile picture
`createdAt`	Account creation timestamp

Post

A top-level content item created by a user.

Field	Purpose
`id`	Unique identifier
`authorId`	Reference to the creating user
`content`	Text content of the post
`likeCount`	Denormalized counter for fast reads
`replyCount`	Denormalized counter for fast reads
`createdAt`	Timestamp used for feed ordering

Reply

A user's response to a post.

Field	Purpose
`id`	Unique identifier
`postId`	The post being replied to
`authorId`	The replying user
`content`	Text content of the reply
`createdAt`	Timestamp

Follow

A directed edge in the social graph: follower → following.

Field	Purpose
`id`	Unique identifier
`followerId`	The user who follows
`followingId`	The user being followed
`createdAt`	Timestamp

A unique compound index on (followerId, followingId) prevents duplicate follow relationships.

Like

Records a user's "like" on a post.

Field	Purpose
`id`	Unique identifier
`userId`	The liking user
`postId`	The liked post
`createdAt`	Timestamp

A unique compound index on (userId, postId) ensures a user can only like a post once.

Indexing strategy (high-level)

Collection	Index	Purpose
Post	`(authorId, createdAt DESC)`	List posts by a user, newest first
Post	`(createdAt DESC)`	Global timeline (future)
Follow	`(followerId)`	Get all accounts a user follows
Follow	`(followingId)`	Get all followers of a user
Follow	`(followerId, followingId)` unique	Prevent duplicates, fast follow-status lookup
Like	`(userId, postId)` unique	Prevent duplicates, fast like-status lookup
Like	`(postId)`	Count/list likes per post

Feed generation pattern

To build the following feed for user U:

Query the Follow collection for all followingId values where followerId = U.
Query the Post collection for documents where authorId IN [followingIds], sorted by createdAt DESC, with cursor-based pagination.

This "fan-out on read" approach is straightforward and works well at the current scale. A precomputed timeline (fan-out on write) would be considered if read latency becomes a concern at larger scale — see Trade-offs & Future Work.

Entity-Relationship Diagram​

Entity descriptions​

User​

Post​

Reply​

Follow​

Like​

Indexing strategy (high-level)​

Feed generation pattern​