Vapor如何将EventLoopFuture<Type>转为对应Type，删除路由报错求解

错误的核心是flatMapThrowing方法的使用场景不对。flatMapThrowing的闭包需要返回非Future类型的普通值，但你在闭包中返回的product.delete(on: req.db).transform(to: .noContent)是EventLoopFuture<HTTPStatus>类型，两者类型不匹配，因此触发编译错误。

把内层的flatMapThrowing替换为flatMap即可，flatMap支持闭包返回Future类型，同时也兼容闭包内主动抛出错误的逻辑，修正后代码如下：

func deleteHandler(_ req: Request) throws -> EventLoopFuture<HTTPStatus> {
    let user = req.auth.get(User.self)
    return Product.find(req.parameters.get("productID"), on: req.db)
        .unwrap(or: Abort(.notFound))
        .flatMap { product in
            // 把原来的flatMapThrowing改为flatMap
            return product.$user.get(on: req.db).flatMap { owner in
                guard try user?.requireID() == owner.requireID() else {
                    throw Abort(.forbidden)
                }
                // 直接返回Future即可匹配类型要求
                return product.delete(on: req.db)
                    .transform(to: .noContent)
            }
        }
}

• 不要使用wait()解决编译问题：wait()会阻塞当前正在运行的EventLoop，违反Vapor的非阻塞设计规则，很容易引发死锁、服务无响应等运行时故障。
• 如果你使用的是Vapor 4+支持async/await的版本，可以改写为异步逻辑，可读性更高：

func deleteHandler(_ req: Request) async throws -> HTTPStatus {
    guard let user = req.auth.get(User.self) else {
        throw Abort(.unauthorized)
    }
    guard let product = try await Product.find(req.parameters.get("productID"), on: req.db) else {
        throw Abort(.notFound)
    }
    let owner = try await product.$user.get(on: req.db)
    guard try user.requireID() == owner.requireID() else {
        throw Abort(.forbidden)
    }
    try await product.delete(on: req.db)
    return .noContent
}

内容的提问来源于stack exchange，提问作者Wendell