Normalizing State

We previously saw how to "normalize" state, by keeping items in an object keyed by item IDs. This gives us the ability to look up any item by its ID without having to loop through an entire array. However, writing the logic to update normalized state by hand was long and tedious. Writing "mutating" update code with Immer makes that simpler, but there's still likely to be a lot of repetition - we might be loading many different types of items in our app, and we'd have to repeat the same reducer logic each time.

Redux Toolkit includes a createEntityAdapter API that has prebuilt reducers for typical data update operations with normalized state. This includes adding, updating, and removing items from a slice. createEntityAdapter also generates some memoized selectors for reading values from the store.