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我正在使用服务器端 swift 框架 Vapor 编写一个 API。我的模型非常简单。我有一个Workout表，它与Circuit表具有对多关系，与表具有对多关系Exercise。当 api 使用者创建一个锻炼时，json 包含锻炼中的所有电路和锻炼。这是一个例子：

{
    ...
    circuits: [{
        ...,
        exercises: [{
            "title": ...
        }, {
            "title": ...
        }]
    }, {
        ...,
        exercises: [{
            "title": ...
        }, {
            "title": ...
        }]
    }]
}

我遇到的问题是当用户在多个电路中进行相同的练习时，会创建重复的练习。我在创建新练习之前查询了数据库，但似乎保存都是异步发生的，这使我无法在保存新练习之前检测到数据库中具有相同 ID/标题的现有练习。这是我的代码：

private func saveExercise(on conn: DatabaseConnectable, with content: WorkoutCreateExerciseContent, for authUser: User) throws -> Future<Exercise> {

        if let exerciseId: UUID = content.id {

            return Exercise.find(exerciseId, on: conn)
                .unwrap(or: Abort(.badRequest, reason: "No exercise for id: \(exerciseId.uuidString)"))

        } else if let title: String = content.title, let isPublicallyVisible: Bool = content.isPublicallyVisible {

            return Exercise.query(on: conn).filter(\.title == title).filter(\.directions == content.directions).first().flatMap({ (possibleMatchingExercise: Exercise?) -> Future<Exercise> in

                if let matchingExercise: Exercise = possibleMatchingExercise {

                    return conn.future(matchingExercise)

                } else {
                    print("xxx Found no match for \(title)")
                    let newExercise: Exercise = Exercise(
                        title: title,
                        directions: content.directions,
                        isPublicallyVisible: isPublicallyVisible
                    )
                    newExercise.userId = authUser.id
                    return newExercise.save(on: conn)

                }

            })

        } else {

            throw Abort(.badRequest, reason: """
                Bad data for exercise. Expecting either of the following:
                {
                    /"id/": /"some id/"
                }
                or
                {
                    /"title/": /"some title/"
                    /"directions/": /"(optional)/",
                    /"isPublicallyVisible/": false
                }
                id takes priority over other properties.
            """)
        }

    }

    private func saveCircuit(on conn: DatabaseConnectable, with content: CircuitCreateContent, order: Int, workoutId: UUID, authUser: User) throws -> Future<Circuit> {

        return try content.exercises.map({ (exerciseContent: WorkoutCreateExerciseContent) throws -> Future<Exercise> in

            let createdExercise: Future<Exercise> = try self.saveExercise(
                on: conn,
                with: exerciseContent,
                for: authUser
            )

            return createdExercise

        })
        .flatten(on: conn)
        .flatMap({ (exercises: [Exercise]) -> Future<Circuit> in

            let circuit: Circuit = Circuit(
                workoutId: workoutId,
                order: order,
                exerciseDuration: content.exerciseDuration,
                restDuration: content.restDuration,
                exerciseIDs: exercises.compactMap({ $0.id })
            )

            return circuit.save(on: conn)

        })

    }

    func saveWorkout(_ conn: DatabaseConnectable,  _ authentiatedUser: User, _ content: WorkoutCreateContent) throws -> Future<Workout> {

        let workout: Workout = content.makeWorkout()

        workout.userId = authentiatedUser.id

        // First save the exercises

        let createdWorkout: Future<Workout> = workout.save(on: conn).flatMap({ (savedWorkout: Workout) -> Future<Workout> in

            let createdCircuits: Future<[Circuit]> = try content.circuits.enumerated().map({ (order: Int, circuitContent: CircuitCreateContent) throws -> Future<Circuit> in

                let createdCircuit: Future<Circuit> = try self.saveCircuit(
                    on: conn, with: circuitContent,
                    order: order,
                    workoutId: savedWorkout.id!,
                    authUser: authentiatedUser
                )

                return createdCircuit

            })
            .flatten(on: conn)

            return createdCircuits.then({ _ -> Future<Workout> in
                return conn.future(savedWorkout)
            })

        })

        return createdWorkout

    }

有人看到我在这里缺少什么吗？Future有没有办法在开始新的之前等待 a完成Future？我是 Vapor 的新手，所以我对 Vapor 的 fluent api 不太熟悉。

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1 回答 1

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假设我们有两个假想的方法返回Future<>

func randomUInt() -> Future<UInt> { ... }
func multiply(value: UInt, by multiplier: UInt) -> Future<UInt> { ... }

我们想将一个随机数乘以 5，但如果随机数为零或 1，则想抛出错误。multiply(value: ,by: )因此我们需要在调用该方法之前等待随机数。

let result: Future<UInt> = randomUInt().flatMap { (value) -> Future<UInt> in
    guard value > 1 else { throw YourError }
    return multiply(value: value, by: 5)
}
于 2020-02-18T17:30:49.683 回答