Offline write strategies and optimistic UI

Choose per operation

Strategy	Flow	Appropriate
online-only	server first, then local	bank transfer/quote requiring live authorization
queued	enqueue, send later	telemetry/non-urgent fire-and-forget
lazy/local-first	local truth + outbox, sync later	notes/tasks/favorites/drafts

An app can be offline-first for reads while requiring online payment writes.

Transactional optimistic update

database.withTransaction {
    taskDao.updateTitle(id, newTitle, SyncStatus.Pending)
    outboxDao.insert(
        OutboxEntity(
            operationId = UUID.randomUUID().toString(),
            entityId = id.value,
            kind = "rename_task",
            payload = encode(newTitle),
        )
    )
}
scheduleSync()

Writing entity and outbox atomically prevents “UI changed but never synced” after crash. UI observes pending local value immediately.

Rollback is not always correct

If server rejects favorite toggle, rollback is simple. If user edited a long note while offline, discarding it is unacceptable. Preserve local draft/conflict and ask user/merge. Product semantics decide.

Multiple local edits

Before upload, collapse superseded operations when safe:

• favorite true→false can coalesce to latest desired state
• increment commands cannot always coalesce without semantics
• append messages must preserve each item/order
• create then delete before sync can cancel both if never externally visible

Use operation identity and base/server version. Do not mutate JSON payload blindly.

User-visible status

Pending/syncing/rejected/conflicted should be visible where consequences matter. “Saved” might mean saved locally; communicate when cloud backup/team visibility is pending.

Undo

Undo before remote commit can cancel/replace pending operation transactionally. After commit, undo is a new compensating operation, not history erasure.

Security

Outbox payload is persisted sensitive data. Minimize fields, encrypt if threat model requires, expire on logout/account removal, and never log full payload.

Optimistic is not imaginary

Optimistic UI should reflect a durable local state transition with pending metadata—not a ViewModel-only visual guess that disappears after process death.

Exercises

1. Choose write strategy for transfer, favorite, analytics, and note edit.
2. Coalesce safe outbox operations.
3. Design undo before and after remote commit.