---
title: Scenarios
description: Short, task-oriented recipes for the things you'll actually need to do — each one assumes you know the basics and gets straight to the goal.
---


These are recipes: "I need to do X — how?" Each is short and assumes you've been through [Get started](/chronicle/get-started/) and understand the [core concepts](/chronicle/concepts/). For the *why* and the full options, follow the links into the reference.

| Recipe | When you reach for it |
|---|---|
| [Rebuild a read model](/chronicle/scenarios/rebuild-a-read-model/) | You changed a projection and need the read model to reflect the new logic |
| [Enforce a unique value](/chronicle/scenarios/enforce-a-unique-value/) | A value (email, ISBN, username) must be unique across a stream |
| [Evolve an event's shape](/chronicle/scenarios/evolve-an-event/) | An event type needs to change without rewriting history |

Missing a recipe you expected? The [feature guides](/chronicle/events/) and [Troubleshooting](/chronicle/troubleshooting/) cover the long tail.