Vapor 4: Children relation not eager loaded, use $ prefix to acces - swift

Question

Currently I am working on a school assignment where we have to build an API using Vapor. I have a few basic API calls working and I am trying a bit more advanced API calls now but I can't get this to work.
I have this function addToParty that is being called when the URL /party/join/:partyID is called with a body
{
"id": "CC1FAC6B-A2B3-471C-A488-147300196981",
"username": "string",
"is_ready": true
}
I am trying to find a party by the partyId and add the user to the list of users of the party.
func addToParty (req: Request) throws -> EventLoopFuture<Party.Output> {
guard let id = req.parameters.get("partyID", as: UUID.self) else {
throw Abort(.badRequest)
}
let input = try req.content.decode(Party.JoinParty.self)
return Party.find(id, on: req.db)
.unwrap(or: Abort(.notFound))
.flatMap { element in
element.users.append(User(id: UUID(input.id), username: input.username, is_ready: input.is_ready))
return element.save(on: req.db)
.map{ Party.Output(code: "200") }
}
}
When I try the code above I get the error Fatal error: Children relation not eager loaded, use $ prefix to access: Children<Party, User>(for: [party_id]): file FluentKit/Children.swift, line 33 from the line
element.users.append(User(id: UUID(input.id), username: input.username, is_ready: input.is_ready))
When I comment this line the code runs and I get a return code.
I tried adding the prefix to element.$users and $User but then it complains about not being able to find element.$users and $User in scope.
Party model
import Fluent
import Vapor
final class Party: Model, Content {
static let schema = "parties"
struct JoinParty: Content {
let id: String
let username: String
let is_ready: Bool
}
struct Output: Content {
let code: String
}
#ID(key: .id)
var id: UUID?
#Field(key: "party_code")
var party_code: String
#Field(key: "host_id")
var host_id: UUID
#Field(key: "is_active")
var is_active: Bool
// change to Game when model is made
#Field(key: "selected_games")
var selected_games: [String]?
// change to Setting when model is made
#Field(key: "settings")
var settings: String
#Field(key: "results")
var results: Array<GameResult>?
#Children(for: \.$party)
var users: [User]
init() { }
init(id: UUID? = nil,
party_code: String,
host_id: UUID,
is_active: Bool,
selected_games: [String]? = nil,
settings: String,
results: Array<GameResult>? = nil) {
self.id = id
self.party_code = party_code
self.host_id = host_id
self.is_active = is_active
self.selected_games = selected_games
self.settings = settings
self.results = results
}
}
User model
import Fluent
import Vapor
final class User: Model, Content {
static let schema = "users"
struct Input: Content {
let id: UUID
let username: String
}
struct Output: Content {
let id: String
let username: String
}
#ID(key: .id)
var id: UUID?
#Field(key: "username")
var username: String
#Field(key: "is_ready")
var is_ready: Bool
#OptionalParent(key: "party_id")
var party: Party?
#Children(for: \.$user)
var gameResults: [GameResult]
init() {}
init(id: UUID? = nil, username: String, is_ready: Bool, partyID: UUID? = nil) {
self.id = id
self.username = username
self.is_ready = is_ready
self.$party.id = partyID
}
}
I have a similar function to update a username from a user already working which is almost the same thing.
func update(req: Request) throws -> EventLoopFuture<User.Output> {
let input = try req.content.decode(User.Input.self)
return User.find(input.id, on: req.db)
.unwrap(or: Abort(.notFound))
.flatMap { user in
user.username = input.username
return user.save(on: req.db)
.map { User.Output(id: user.id!.uuidString, username: user.username) }
}
}
Any help would be really appreciated.
Thank you in advance.

Answer 1

Unfortunately, adding children to a parent model is not that intuitive yet. I hope that someday we can get that added, but it's not there yet. Fluent 5 maybe?
Anyway, what you'll need to do instead is create your new User model, passing in the party's ID value to the partyID initializer parameter, and then save the User model.
let user = User(id: UUID(input.id), username: input.username, is_ready: input.is_ready, partyID: element.id)
return user.save(on: request.db)
So your method should end up looking like this:
func addToParty(req: Request) throws -> EventLoopFuture<Party.Output> {
guard let id = req.parameters.get("partyID", as: UUID.self) else {
throw Abort(.badRequest)
}
let input = try req.content.decode(Party.JoinParty.self)
return Party.find(id, on: req.db).unwrap(or: Abort(.notFound)).flatMap { element in
return User(
id: UUID(input.id),
username: input.username,
is_ready: input.is_ready,
partyID: element.id
).save(on: req.db)
}.transform(to: Party.Output(code: "200"))
}