Implementing various methods of caching in Rails is relatively simple, and in most basic cases Rails handles cache invalidation out of the box or with minimal code. But when using many-to-many associations, propagating changes in one object to all its associated objects needs some setting up so that Rails can handle cache invalidation. In “Invalidating caches when using many-to-many associations in Rails,” I talk about various methods of achieving this, and why one should choose one over the other.