Answer by Tony Ngo for NGRX reducers using the same state object

At first part you already mention that spliting reducer to small reducer so I would not mention again.

Secondly you can use NGRX/Entity to let NGRX handle CRUD operation for you so the code complexity would be reduce because NGRX/Entity already include some API allow developer to do CRUD operation on the state.

Example:

const userReducer = createReducer(  initialState,  on(UserActions.addUser, (state, { user }) => {    return adapter.addOne(user, state)  }),  on(UserActions.upsertUser, (state, { user }) => {    return adapter.upsertOne(user, state);  }),  on(UserActions.addUsers, (state, { users }) => {    return adapter.addMany(users, state);  }),  on(UserActions.upsertUsers, (state, { users }) => {    return adapter.upsertUsers(users, state);  }),  on(UserActions.updateUser, (state, { user }) => {    return adapter.updateOne(user, state);  }),  on(UserActions.updateUsers, (state, { users }) => {    return adapter.updateMany(users, state);  }),  on(UserActions.mapUsers, (state, { entityMap }) => {    return adapter.map(entityMap, state);  }),  on(UserActions.deleteUser, (state, { id }) => {    return adapter.removeOne(id, state);  }),  on(UserActions.deleteUsers, (state, { ids }) => {    return adapter.removeMany(ids, state);  }),  on(UserActions.deleteUsersByPredicate, (state, { predicate }) => {    return adapter.removeMany(predicate, state);  }),  on(UserActions.loadUsers, (state, { users }) => {    return adapter.addAll(users, state);  }),  on(UserActions.clearUsers, state => {    return adapter.removeAll({ ...state, selectedUserId: null });  }));