Apollo-ios: Generic parameter 'Mutation' could not be inferred

[JulienLevallois]

Hi ! I got this error with mutation & query too. Do you know why ?

Thanks

[rusty-jules]

Same issue here. Swift 4.2 Xcode 10

[mayuritalaviya]

Same issue in 'mutation' and 'fetch' with xcode 10. Any one got solution ??

[kadishmal]

The following worked for me:

let mutationInput = CreateUserSettingsInput(id: username, pauseSync: false, lastSyncDate: Int(NSDate().timeIntervalSince1970))
let mutation = CreateUserSettingsMutation(input: mutationInput)

self.appSyncClient?.perform(mutation: mutation) { (result, error) in
    ...
}

[jxltom]

It is because the wrong field in result is accessed.

result.data.yourfield is OK but result.data.somewrongfield will raise this error.

[juanpdelat]

@jxltom is right, using the proper field fixed it for me. I believe the error message should be improved.

[designatednerd]

Unfortunately the error message is coming from Swift rather than from us. I know Swift has been working to make its error messages from generics a bit less opaque, but there's not a lot we can do about it.

I'm going to close this one out, but please feel free to open a new issue if you run into any further problems!

[michaelryannewell]

There is no (result, error), just a response object that can be mapped to result or error. The code below highlights the new syntax. The new response object is called (result). Notice that it replaces (result, error):

let mutationInput = CreateUserSettingsInput(id: username, pauseSync: false, lastSyncDate: Int(NSDate().timeIntervalSince1970))
let mutation = CreateUserSettingsMutation(input: mutationInput)

self.appSyncClient?.perform(mutation: mutation) { (result) in

            do {

                // success value

                let success = try result.get()
                print("success: \(success)")

                // data errors

                let dataErrors = success.errors
                print("dataErrors: \(dataErrors)")

                // data

                let data = success.data
                print("data: \(data)")

                // your field

                success.data?.yourField

                // or

                data?.yourField


            } catch {

                // mutation error

                let error = result.mapError({ (error) -> Error in

                    return error

                })

                print("error: \(error)")

            }

}

[designatednerd]

Yep - this is also a totally valid way to access the Result. Personally I prefer the switch way of accessing it as I find it a bit easier to read:

client.perform(mutation: mutation) { result in
  switch result {
  case .success(let graphQLResult):
    // Deal with GraphQLResult and its data and/or errors properties here
  case .failure(let error): 
    // deal with network errors here 
  }
}

[michaelryannewell]

Yep - this is also a totally valid way to access the Result. Personally I prefer the switch way of accessing it as I find it a bit easier to read:

client.perform(mutation: mutation) { result in
  switch result {
  case .success(let graphQLResult):
    // Deal with GraphQLResult and its data and/or errors properties here
  case .failure(let error): 
    // deal with network errors here 
  }
}

Thank you @designatednerd I learned something new today!

You can view the result enum for Swift in the docs as Swift > Result

/// A value that represents either a success or a failure, including an
/// associated value in each case.
public enum Result where Failure : Error {

/// A success, storing a `Success` value.
case success(Success)

/// A failure, storing a `Failure` value.
case failure(Failure)