Sql 在蒸汽流利中查找所有具有空多对多关系的项目

根据vapor文档中的示例:

// Example of a pivot model.
final class PlanetTag: Model {
    static let schema = "planet+tag"

    @ID(key: .id)
    var id: UUID?

    @Parent(key: "planet_id")
    var planet: Planet

    @Parent(key: "tag_id")
    var tag: Tag

    init() { }

    init(id: UUID? = nil, planet: Planet, tag: Tag) throws {
        self.id = id
        self.$planet.id = try planet.requireID()
        self.$tag.id = try tag.requireID()
    }
}

final class Planet: Model {
    // Example of a siblings relation.
    @Siblings(through: PlanetTag.self, from: \.$planet, to: \.$tag)
    public var tags: [Tag]
}

final class Tag: Model {
    // Example of a siblings relation.
    @Siblings(through: PlanetTag.self, from: \.$tag, to: \.$planet)
    public var planets: [Planet]
}

我怎样才能用fluent查询所有没有标签的行星？

Planet.query(on: req.db).filter(?).all()

EDIT: Solution but with async/await

let pivots = try await PlanetTag.query(on: req.db).unique().all()
let planetsWithTags = pivots.map { $0.$planet.id }
let planetsWithoutTags = Planet.query(on: req.db).filter(\.$id !~ planetsWithTags)
    
return try await planetsWithoutTags.paginate(for: req).map(\.detail)