Solving Riverpod’s Family Provider Cache Dilemma with Signals & mapSignal

The key issue in Flutter apps using Riverpod 3 family providers with backend REST APIs is stale data appearing across multiple cached query results. For example, if a user moves a task from "In Progress" to "Done", the task may still appear in the "In Progress" column in the UI until the next full refetch from the server. Similarly, user name changes in embedded task objects are not reflected without a full refetch.

This stale data stems from using parameterized fetchers as isolated state containers within each family provider. Each filter creates its own independent copy of the data, so updating one instance doesn't propagate changes to the others. This leads to overlapping subset inconsistencies and stale relational data.

The solution is to switch to a normalized entity store using the Signals library in Dart. Instead of multiple isolated providers, all entities live in a single mapSignal shared by all needed locations. Filtered views are then derived as computed signals that reactively reference the normalized store. This eliminates duplicate objects, enables in-place entity updates without network overhead, and allows fine-grained reactivity as entities change.

The mapSignal provides key-level reactivity, so updating a single entity only notifies listeners for that specific key. This avoids the need for full invalidations or complex mutation loops between providers. By normalizing the data and deriving projections, the app gains a single source of truth with reactive views that stay perfectly in sync as the underlying data evolves.