Normalized entity storage
Model a collection of records in a slice using the standard normalized IDs-plus-entities structure.
Redux Toolkit · Type Alias
EntityAdapter
EntityAdapter is the plain-object adapter type for one normalized entity collection. It bundles CRUD reducers, identity and sorting configuration, initial-state creation, and memoized selector generation.
How it works
EntityAdapter is the plain-object type returned by createEntityAdapter. It groups generated CRUD case reducers, the configured identity and sorting callbacks, initial-state creation, and selector-generation methods for one normalized entity type.
Syntax
type EntityAdapter<T, Id extends EntityId> = EntityStateAdapter<T, Id> & EntitySelectors<T, Id>Returns
An EntityAdapter instance: a plain object containing generated CRUD reducers, the configured callbacks, getInitialState, and selector-generation functions.
Key points
- createEntityAdapter returns an EntityAdapter containing ready-made reducers and selectors for a normalized collection.
- The type describes a plain object, not a class instance, with generated reducer functions and adapter utilities.
- The adapter retains the identity and ordering callbacks supplied when the adapter is created.
- getInitialState creates the normalized starting state for the entity collection.
- getSelectors can produce memoized selectors either for the entity state directly or for a selected slice of root state.
- CRUD reducer methods form the adapter's main operational API for changing normalized entity state.
Common mistakes
- Entities stored through the adapter must remain serializable plain objects rather than class instances.
- Generated reducer methods can be supplied directly as case reducers, but manual calls should occur where the state is an Immer Draft.
Example: Typing an entity adapter
import { createEntityAdapter, type EntityAdapter } from '@reduxjs/toolkit'
type User = { id: string; name: string }
const users: EntityAdapter<User> = createEntityAdapter<User>()
const state = users.getInitialState()
users.addOne(state, { id: '1', name: 'Ada' })
console.log(users.getSelectors().selectAll(state))The adapter is typed as EntityAdapter<User>, then used to create normalized state and add an entity.
When to use it
CRUD reducer logic
Reuse generated add, update, replace, upsert, and remove operations instead of writing collection reducers manually.
Entity selectors
Create memoized select-all and select-by-ID accessors for a collection or a nested slice.
Interview questions
QWhat does EntityAdapter represent?
EntityAdapter is the adapter instance type produced by createEntityAdapter. It exposes the generated reducers, the configured selectId and sortComparer callbacks, getInitialState, and selector-generation methods.
Follow-up: Why use an adapter instead of handwritten normalized reducers? It standardizes the normalized state shape and supplies reusable CRUD reducers and memoized selectors.
QWhat capabilities does an EntityAdapter expose?
Its CRUD methods operate on an entity state containing IDs and an entity lookup table. Methods include operations such as addOne, setAll, updateOne, upsertMany, and removeMany.
Follow-up: How can those methods be used in a slice? Pass them as case reducers or invoke them as mutating helpers inside Immer-backed reducer logic.
QHow does EntityAdapter support reading state?
The adapter can generate selectors for normalized data, including selectors for all entities and an entity by ID. getInitialState creates the empty normalized state used by those selectors and reducers.
Follow-up: How can the adapter be scoped to a nested slice? Supply a selector that returns that slice to getSelectors, producing selectors rooted at the Redux state.
Related
createEntityAdapterEntityStateEntitySelectorsEntityStateAdaptercreateSlicecreateReducer