查询在Vapor中如何工作？

Question

How to return user if based on facebook user ID it already exist, and create a new user if not exist in Vapor ? You can see how I tried fetch data, but get error.

final class User: Content {
    var id: Int?
    var fbId: String

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

router.get("user") { (request) -> Future<User> in
    return Future.map(on: request) { () -> User in
        let fbId = try request.query.get(String.self, at: "fbId")
        return User.query(on: request).filter(\.fbId == fbId).first().map { (user) -> (U) in
            if user == nil {
                user = User(fbId: fbId)
            }
            return user
        }
    }
}

Answer 1

You have a few things going on here. To start with you don't need the first Future.map - not sure what that's doing.

Then you have the issue of the compiler - you have to return the same type in each closure and the function, which is awkward because if you already have a user you can return that, if you don't you need to create and save one, which returns Future<User> , which is not the same to User .

So to answer your question, U there should be User , but really you want to change first().map to first().flatMap in which case U becomes Future<User> . Then you can do something like:

router.get("user") { req -> Future<User> in
    let fbID = try req.query.get(String.self, at: "fbId")
    return User.query(on: req).filter(\.fbId == fbID).first().flatMap { user in
        let returnedUser: Future<User>
        if let foundUser = user {
            returnedUser = req.future(foundUser)
        } else {
            let newUser = User(fbId: fbID)
            returnedUser = newUser.save(on: req)
        }
        return returnedUser
    }
}

To solve your problems. Hope that helps!

Answer 2

.map { (user) -> (U) in

This defines that you get a user into the closure and have to return a U . In your example you want to return a User (so change U to User ).

If you want to create the user (in case it is nil ) you probably also want to store it in the database? If that's the case, you'll have to change map to flatMap and update like this:

.flatMap { (user) -> EventLoopFuture<User> in
  if user == nil {
    return User(fbId: fbId).save(on: req)
  }
  return req.future(user)
}