如何在vapor 4中选择连接表中的所有列？

import Vapor
import Fluent

final class User: Model {
    static let schema = "users"
    
    @ID(key: .id)
    var id: UUID?
    
    @Field(key: "name")
    var name: String
    
    @Children(for: \.$user)
    var posts: [Post]
    
    init() {}
    
    init(id: UUID? = nil, name: String) {
        self.id = id
        self.name = name
    }
}

final class Post: Model {
    static let schema = "posts"
    
    @ID(key: .id)
    var id: UUID?
    
    @Field(key: "title")
    var title: String
    
    @Parent(key: "user_id")
    var user: User
    
    init() {}
    
    init(id: UUID? = nil, title: String, userID: User.IDValue) {
        self.id = id
        self.title = title
        self.$user.id = userID
    }
}

func getAllColumnsFromJoinTable() throws {
    let db = ...
    
    let columns = try db.schema(User.schema)
        .join(Post.self, on: \User.$id == \Post.$userID)
        .fields
        .map { $0.name }
    
    print(columns)
}