Counter Cache In Vapor 3

MyModels.swift

final class MyUser: PostgreSQLModel {
    static let idKey: WritableKeyPath<MyUser, Int?> = \MyUser.id
    var id: Int?
    var myParticipationsCount: Int = 0

    init(id: Int? = nil) {
        self.id = id
    }
}


final class MyParticipation: PostgreSQLModel {
    static let idKey: WritableKeyPath<MyParticipation, Int?> = \MyParticipation.id
    var id: Int?
    var userId: MyUser.ID

    init(id: Int? = nil, userId: MyUser.ID) {
        self.id = id
        self.userId = userId
    }

    var user: Parent<MyParticipation, MyUser> {
        return parent(\.userId)
    }

    func didCreate(on connection: PostgreSQLConnection) throws -> EventLoopFuture<MyParticipation> {
        try updateCounterCache(connection)
        return Future.map(on: connection, { self })
    }

    func didUpdate(on connection: PostgreSQLConnection) throws -> EventLoopFuture<MyParticipation> {
        try updateCounterCache(connection)
        return Future.map(on: connection, { self })
    }
    func willDelete(on connection: PostgreSQLConnection) throws -> EventLoopFuture<MyParticipation> {
        try updateCounterCache(connection, willDelete: true)
        return Future.map(on: connection, { self })
    }

    func updateCounterCache(_ connection: PostgreSQLConnection, willDelete: Bool = false) throws {
        _ = try user.get(on: connection).flatMap(to: MyUser.self, { myUser in
            return try MyParticipation
                .query(on: connection)
                .filter(\MyParticipation.userId == self.userId)
                .count()
                .flatMap(to: MyUser.self, { participationCount in
                    if(willDelete) {
                        myUser.myParticipationsCount = participationCount
                    } else {
                        myUser.myParticipationsCount = participationCount - 1
                    }
                    return myUser.save(on: connection)
                })
        })
    }
}