Swift converting Decodable struct to Dictionary

Question

I have created a decoadable struct that will be used to parse data stored in firebase.

struct DiscussionMessage: Decodable {
    var message: String
    var userCountryCode: String
    var userCountryEmoji: String
    var messageTimestamp: Double
    var userName: String
    var userEmailAddress: String
    var fcmToken: String?
    var question: String?
    var recordingUrl: String?
}

I want to use this struct to also store data in firebase. But I get the error:

*** Terminating app due to uncaught exception 'InvalidFirebaseData', reason: '(setValue:) Cannot store object of type __SwiftValue at . Can only store objects of type NSNumber, NSString, NSDictionary, and NSArray.' terminating with uncaught exception of type NSException

When I store the data like this:

let message = DiscussionMessage(message: messageTextView.text, userCountryCode: userCountryCode, userCountryEmoji: userCountryEmoji, messageTimestamp: timestamp, userName: userName, userEmailAddress: userEmail, fcmToken: nil, question: nil, recordingUrl: nil)       
        
messagesReference.childByAutoId().setValue(message)

Is there a way to convert a decodable object to a dictionary so I can store it in firebase?

Answer 1

You don't need it to be Decodable. What you need is to be able to encode it (Encodable). So start by declaring your structure as Codable. After encoding it you can convert your data into a dictionary using JSONSerialization jsonObject method:

extension Encodable {
    func data(using encoder: JSONEncoder = .init()) throws -> Data { try encoder.encode(self) }
    func string(using encoder: JSONEncoder = .init()) throws -> String { try data(using: encoder).string! }
    func dictionary(using encoder: JSONEncoder = .init(), options: JSONSerialization.ReadingOptions = []) throws -> [String: Any] {
        try JSONSerialization.jsonObject(with: try data(using: encoder), options: options) as? [String: Any] ?? [:]
    }
}

---

extension Data {
    func decodedObject<D: Decodable>(using decoder: JSONDecoder = .init()) throws -> D {
        try decoder.decode(D.self, from: self)
    }
}

---

extension Sequence where Element == UInt8 {
    var string: String? { String(bytes: self, encoding: .utf8) }
}

---

I would also declare the srtuct properties as constants. If you need to change any value just create a new object:

struct DiscussionMessage: Codable {
    let message, userCountryCode, userCountryEmoji, userName, userEmailAddress: String
    let messageTimestamp: Double
    let fcmToken, question, recordingUrl: String?
}

---

let message: DiscussionMessage = .init(message: "message", userCountryCode: "BRA", userCountryEmoji: "", userName: "userName", userEmailAddress: "email@address.com", messageTimestamp: 1610557474.227274, fcmToken: "fcmToken", question: "question", recordingUrl: nil)

do {
    let string = try message.string()
    print(string)      // {"fcmToken":"fcmToken","userName":"userName","message":"message","userCountryEmoji":"","userEmailAddress":"email@address.com","question":"question","messageTimestamp":1610557474.2272739,"userCountryCode":"BRA"}
    
    let dictionary = try message.dictionary()
    print(dictionary)  // ["userName": userName, "userEmailAddress": email@address.com, "userCountryEmoji": , "messageTimestamp": 1610557474.227274, "question": question, "message": message, "fcmToken": fcmToken, "userCountryCode": BRA]
    
    let data = try message.data()      // 218 bytes
    let decodedMessages: DiscussionMessage = try data.decodedObject()
    print("decodedMessages", decodedMessages)    // ecodedMessages DiscussionMessage(message: "message", userCountryCode: "BRA", userCountryEmoji: "", userName: "userName", userEmailAddress: "email@address.com", messageTimestamp: 1610557474.227274, fcmToken: Optional("fcmToken"), question: Optional("question"), recordingUrl: nil)
} catch {
    print(error)
}

Answer 2

I'm going to toss out an answer and see if it helps.

I would suggest extending Encodable to allow any object that conforms to return a dictionary of itself that can be written to Firebase.

Here's the extension

extension Encodable {
    var dict: [String: Any]? {
        guard let data = try? JSONEncoder().encode(self) else { return nil }
        return (try? JSONSerialization.jsonObject(with: data, options: .allowFragments)).flatMap { $0 as? [String: Any] }
    }
}

and then just a change to the struct

struct DiscussionMessage: Encodable {
   ...your properties...
}

And the code

let msg = DiscussionMessage(data to populate with)
let dict = msg.dict
messagesReference.childByAutoId().setValue(dict)

Keep in mind that the Realtime Database has no nil - any node that has no value does not exist so only the properties that have values will be written.

Oh - and ensure the properties are valid Firebase types of NSNumber, NSString, NSDictionary, and NSArray (and Bool)