Redux state shape without data duplication - redux

Question

I'm new to redux and it's hard to grasp how to implement good state shape without duplicating data, in case I need to update it, and naive way would be to update in few places, but that would negate the single source of truth.
We fetch user profile and posts from API server:
www.api.com/users/placeholder
{
"user": {
"username": "placeholder",
"bio": "It's my bio",
"profileImage": "http://via.placeholder.com/350x150",
"isViewerFollowing": false
}
}
www.api.com/posts?author=placeholder
{
"posts":[{
"id": "1",
"caption":"caption placeholder",
"image":"http://via.placeholder.com/1000x1000",
"createdAt": "2017-08-18T03:22:56.637Z",
"updatedAt": "2016-08-18T03:48:35.824Z",
"isLikedbyViewer": false,
"likesCount": 0,
"author": {
"username": "placeholder",
"bio": "It's my bio",
"profileImage": "http://via.placeholder.com/350x150",
"isViewerFollowing": false,
}
},
{
"id": "2",
"caption":"caption placeholder",
"image":"http://via.placeholder.com/1000x1000",
"createdAt": "2017-08-18T03:22:56.637Z",
"updatedAt": "2016-08-18T03:48:35.824Z",
"isViewerLiked": false,
"likesCount": 0,
"author": {
"username": "placeholder",
"bio": "It's my bio",
"profileImage": "http://via.placeholder.com/350x150",
"isViewerFollowing": false,
}
}],
"postsCount": 2
}
For example, we have separate reducers for users and posts, and user wants to follow user/author, then we would need to update information in two reducers. So my final question would be, could someone hint me what would good state shape look like in this particular example ?
Thanks!

Answer 1

You should normalize your Redux state: instead of saving the entire author object for every post, you should just save the authorId.
Since you ensure that when you have a post object in the posts branch of your Redux state, you also have the related author in the authors branch, to retrieve all the posts with their author's data you can create a selector:
export function getPosts(reduxState) {
return reduxState.posts.map(post => {
const author = reduxState.authors.find(a => a.id === post.authorId);
return {
...post,
author
};
});
}