SwiftUI - How to structure relational data in state - swift

Question

I'm new to Swift and I am having trouble understanding how to structure relational data in a larger app.
Consider this api json response
// posts
{
"entities": {
"posts": [
{
"id": "1",
"content": "I am a post!"
"user": {
"id": "1",
"username": "user1"
}
},
{
"id": "2",
"content": "I am another post!"
"user": {
"id": "1",
"username": "user1"
}
}
]
}
}
// posts/featured
{
"entities": {
"posts": [
{
"id": "2",
"content": "I am another post!"
"user": {
"id": "1",
// username is not needed in the featured posts UI
}
}
]
}
}
There are a couple of things to keep in mind:
posts and posts/featured represent two independent screens on the app, each displaying a separate set of posts. Overlaps are allowed, as in the response above.
The api is tied to the app views, i.e. it will return only the data that is directly used in the app. posts/featured does not show the username, hence it is not returned by the api.
If a post's content is changed in posts, that update should automatically be applied to the same post in posts/featured only if it is there.
My attempt
Here is how I attempted to model this.
The Post and User structs
struct Post {
let id: String
var content: String?
var user: String?
init(json: [String: Any]) {
let id = json["id"] as! String
let content = json["content"] as? String ?? nil
let user = json["user"] as? [String: Any] ?? nil
self.id = id
self.content = content
self.user = user != nil ? user!["id"] as? String : nil
}
}
struct User {
let id: String
var username: String?
init(json: [String: Any]) {
let id = json["id"] as! String
let username = json["username"] as? String ?? nil
self.id = id
self.username = username
}
}
My entityState
class EntityState: ObservableObject {
#Published var posts: [String: Post]
#Published var users: [String: User]
... more stuff
}
Updating data across screens
My only solution is to normalize the state, and have Post.user be a String representing the User.id. With that, I keep in EntityState the dictionaries of posts and users, and in my ViewModels, I keep a local array of strings representing the postIds of the specific screen.
To update the data, only one update is required in the EntityState model and it will propagate everywhere it is being referenced by id.
Using Post and User struct in the code
Since User.username will sometimes be empty depending on where it is requested, it forces me to deal with conditionals or worse, use User.username! everywhere, which I don't think is correct, yet I am unsure of a better way.
What is the best way to structure this? I also control the api, so I am flexible in returning different data.

Answer 1

let json = """
{
"entities": {
"posts": [
{
"id": "1",
"content": "I am a post!",
"user": {
"id": "1",
"username": "user1"
}
},
{
"id": "2",
"content": "I am another post!",
"user": {
"id": "1",
"username": "user1"
}
},
{
"id": "2",
"content": "I am another post!",
"user": {
"id": "1"
}
}
]
}
}
"""
// Simulate data received from a network call
let data = json.data(using: .utf8)!
struct Entity: Codable {
var entities: [String : [Post]]
}
struct Post: Codable {
let id: String
var content: String?
var user: User?
}
struct User: Codable {
let id: String
var username: String?
}
do {
let entity = try JSONDecoder().decode(Entity.self, from: data)
print(entity)
}catch {
print(error)
}
Inspecting in the console:
po entity
▿ Entity
▿ entities : 1 element
▿ 0 : 2 elements
- key : "posts"
▿ value : 3 elements
▿ 0 : Post
- id : "1"
▿ content : Optional<String>
- some : "I am a post!"
▿ user : Optional<User>
▿ some : User
- id : "1"
▿ username : Optional<String>
- some : "user1"
▿ 1 : Post
- id : "2"
▿ content : Optional<String>
- some : "I am another post!"
▿ user : Optional<User>
▿ some : User
- id : "1"
▿ username : Optional<String>
- some : "user1"
▿ 2 : Post
- id : "2"
▿ content : Optional<String>
- some : "I am another post!"
▿ user : Optional<User>
▿ some : User
- id : "1"
- username : nil
RE: Well, this structure doesn't provide any details/explanation regarding state normalisation and why you didn't use it, nor does it provide any explanation for dealing with optional properties of structs in the code. It also doesn't address the problem of updating one Post/User entity and having that update be reflected across the app in multiple states. I've listed in my question 3 "requirements" to keep in mind, and my attempted solution for each at the end. I was hoping for a more complete answer around those points of discussion. – Darius Mandres 3 hours ago
State management in SwiftUI does not happen in the data. These structs are used for bringing in json to a more useable format. A popular way to do that in swift is by using structs. This will likely happen async on a background thread depending how you are getting your json. If you want to lean about state management in SwiftUI I suggest looking here https://developer.apple.com/documentation/swiftui/state-and-data-flow
2)Optionals are a part of swift. They replaced nil pointers of objective-c which were also very popular. If you want to avoid them you should consider two struct one Posts one Featured. In most cases if I'm dealing with ui personally I like to use a default value. Such as Text(userName ?? "") or Text(userName ?? "User Name Unavailable"), but that's up to you as a programmer, If by mistake a featured finds its way into posts should your app crash so you can find it?
Structs in swift are copies they are passed by copy not reference. If you modify a copy it applies to that copy. You can use a class and copy a pointer throughout the app, or you can notify people using that same struct of changes.
I think you may want to consider breaking your question up into specifics and posting individual questions if you still need help.