nested-data-reducer.js

import { combineReducers } from 'redux'
import { createAction, handleActions } from 'redux-actions'

const authorFetched = createAction('AUTHOR_FETCHED')
const bookFetched   = createAction('BOOK_FETCHED')

const literaryReducer = handleActions({
  // maybe an author has a bunch of books as sub-resources
  AUTHOR_FETCHED: (state, action) => {
    const author = action.payload
    const { books } = author

    const authors = Object.assign({}, state.authors, { [author.id]: author })
    const books = Object.assign({}, state.books, books)

    return { authors, books }
  },

  // a book has an author sub-resource
  BOOK_FETCHED: (state, action) => {
    const book = action.payload
    const { author } = book

    const authors = Object.assign({}, state.authors, { [author.id]: author })
    const books = Object.assign({}, state.books, { [book.id]: book })

    return { authors, books }
  },
}, {
  authors: {},
  books: {},
})

export const authorSelector = id => state => state.literary.authors[id]
export const bookSelector = id => state => state.literary.books[id]

export default combineReducers({
  literary: literaryReducer,
  otherStuff: otherReducer,
})