unreadExists

UnreadExists is a boolean predicate used in software systems to indicate whether there exists at least one unread item in a collection, such as emails, messages, notifications, or tasks. It is commonly exposed as a function, API endpoint, or query clause that can be evaluated without retrieving the full set of items.

The predicate typically accepts context parameters such as a user identifier, a container or folder identifier, and possibly an item type. It returns true when there is at least one item marked unread (or lacking a read timestamp) that matches the criteria, and false otherwise. In some designs unreadExists is purely read-only and has no side effects; in others it may be combined with filtering to scope to specific time ranges or states.

Example in SQL: SELECT EXISTS (SELECT 1 FROM messages WHERE user_id = ? AND is_read = FALSE); In a functional style, unreadExists(user, folder) might be implemented as exists(filter(is_unread, itemsInFolder(user, folder))).

Usage and performance: unreadExists is often used to decide whether to fetch full item lists or to render notification icons. Implementations usually rely on appropriate indexing on the unread flag and the relevant identifiers to avoid full scans. Treat unreads carefully in concurrent environments to prevent race conditions; consider read timestamps or optimistic locking if marks change frequently.

Variants: some systems track per-item read timestamps instead of a boolean; others provide a per-user unread count in addition to the boolean predicate. While closely related to counts and lists of unread items, unreadExists focuses on existence to optimize operations and rendering.