在没有Seri​​alizeObject的情况下在F＃中解析Firebase JSON

Question

I am getting the following JSON from firebase:

{"listings":{"-cecececee-oha-":{"listing_id":"-xsxsxsxsxs-oha-","location":"Edinburgh"},"-xsxssxxsxs":{"listing_id":"-xsxsxsxs","location":"Edinburgh","messages":{"xsxsxsxs":{"-xsxssxxs":{"senderId":"wdwdwwd","senderName":"wddwdw","text":"Hey there"},"-L19r0osoet4f9SjBGE7":{"senderId":"cddccdcd","senderName":"dccd","text":"Hi"}}}},"-cdcdcdcd":{"listing_id":"-cdcdcdcd","location":"Edinburgh","messages":{"879dUqGuiXSd95QHzfhbSs05IZn2":{"-L1i6c7sGf3BcF2cCSCu":{"senderId":"879dUqGuiXSd95QHzfhbSs05IZn2","senderName":"cddcdcdcd","text":"cdcddccdcd"}},"cddcdccdcd":{"-L19FGCMuQACjYKCFEwV":{"senderId":"Rp7ytJdEvZeMFgpLqeCSzkSeTyf1","senderName":"dccdcdcd","text":"Hey"},"-cdcdcdcdcd-":{"senderId":"cdcdcdcd","senderName":"dcdccdcd","text":"cdcddccd"},"-cdcdcdcd":{"senderId":"cdcdcdcdcd","senderName":"cdcdcdcdcd","text":"How are you"}}}},"-cdcdcdcd-dccd":{"listing_id":"-cdcdcdcd-JCbiAnN","location":"Edinburgh"},"-dccdcdcdcd-EKCq2":{"listing_id":"-cdcdcdcd-EKCq2","location":"Edinburgh"},"-cddccdcdcd":{"listing_id":"-cdcdcddcdc","location":"Edinburgh"}}}

I am currently parsing this in Swift as follows, using the Firebase API:

 _ = Database.database().reference().child("users").child(UserDefaults.standard.object(forKey: "uid") as! String).observeSingleEvent(of : .value, with: { (snapshot) in
        var matches_list = [ChatMatch]()
        if let matches = snapshot.childSnapshot(forPath: "listings").value as? [String:AnyObject] {
            for (str,_) in matches {
                if let dictionary = snapshot.childSnapshot(forPath: "listings").childSnapshot(forPath: str).value as? [String:AnyObject] {
                    let location = dictionary["location"] as! String
                    let a = ChatMatch()
                    a.id = str
                    a.location = location
                    if let pairs = snapshot.childSnapshot(forPath: "listings").childSnapshot(forPath: str).childSnapshot(forPath:"messages").value as? [String:AnyObject] {
                        for (str1,_) in pairs {
                            if let dic = snapshot.childSnapshot(forPath: "listings").childSnapshot(forPath: str).childSnapshot(forPath:"messages").childSnapshot(forPath: str1).value as? [String:AnyObject] {
                                for (str2, _)  in dic {
                                    if let dic2 = snapshot.childSnapshot(forPath: "listings").childSnapshot(forPath: str).childSnapshot(forPath:"messages").childSnapshot(forPath: str1).childSnapshot(forPath: str2).value as? [String:AnyObject] {
                                        if let senderid = dic2["senderId"] as? String {
                                            if (senderid != UserDefaults.standard.object(forKey: "uid") as! String) {
                                                a.matchid = senderid
                                            }
                                        }
                                        if let senderName = dic2["senderName"] as? String {
                                            if (senderName != UserDefaults.standard.object(forKey: "name") as! String) {
                                                a.matchName = senderName
                                                matches_list.append(a)
                                                break
                                            }
                                        }
                                    }
                                }



                            }
                        }
                }
            }
        }
        }

        for match in matches_list {

            Database.database().reference().child("listings").child(match.location!).child(match.id!).observeSingleEvent(of: .value, with: { (snapshot2) in
                if let dict = snapshot2.value as? [String : Any] {
                    let new_listing = Listing()

                    let fromString = dict["from"] as! String
                    let toString = dict["to"] as! String
                    let landlordId = dict["landlord_id"] as! String
                    let landlordName = dict["name"] as! String
                    let listingId = dict["listing_id"] as! String
                    let pic1url = dict["pic_1_url"] as! String
                    let pic2url = dict["pic_2_url"] as! String
                    let pic3url = dict["pic_3_url"] as! String
                    let pic4url = dict["pic_4_url"] as! String
                    let pic5url = dict["pic_5_url"] as! String
                    let pricepernight = dict["price_per_night"] as! String
                    let postcode = dict["postcode"] as! String
                    let location = dict["location"] as! String

                    let dateFormatter = DateFormatter()
                    dateFormatter.dateFormat = "dd/mm/yyyy"
                    dateFormatter.timeZone = TimeZone(abbreviation: "GMT+0:00")

                    let fromdate = dateFormatter.date(from: fromString)
                    new_listing.from = fromdate

                    let todate = dateFormatter.date(from: toString)
                    new_listing.to = todate

                    new_listing.landlordId = landlordId
                    new_listing.landlordName = landlordName
                    new_listing.listingId = listingId
                    new_listing.pricePerNight = Int(String(pricepernight.suffix(pricepernight.count - 1)))!
                    if (pic1url != "none") {
                        new_listing.pic1url = URL(string: pic1url)
                    }
                    if (pic2url != "none") {
                        new_listing.pic2url = URL(string: pic2url)
                    }
                    if (pic3url != "none") {
                        new_listing.pic3url = URL(string: pic3url)
                    }
                    if (pic4url != "none") {
                        new_listing.pic4url = URL(string: pic4url)
                    }
                    if (pic5url != "none") {
                        new_listing.pic5url = URL(string: pic5url)
                    }
                    new_listing.postcode = postcode
                    new_listing.location = location
                    new_listing.partnername = match.matchName
                    new_listing.partnerid = match.matchid
                    listings.append(new_listing)
                    if (matches_list.index(of: match) == matches_list.count - 1) {
                        completionHandler(true, listings)
                        return
                    }
                }
            })
        }
        if (matches_list.count == 0) {
            completionHandler(false, listings)
        }

    })
}

As you can see, I make my way through the JSON by converting into dictionaries and looping through pairs.

I need to do the same thing now in F# . I manage to obtain the JSON using the REST API as there is no native API for Firebase in F#. However, I am completely lost when it comes to parsing this JSON. I managed to come up with the following code:

let myCallbackGetChats (reader:IO.StreamReader) url = 
    let html = reader.ReadToEnd()
    let reader : JsonTextReader = new JsonTextReader(new StringReader(html))

    while (reader.Read()) do 
        if reader.Value <> null then 
            let value = reader.Value :?> String 

This allows me to loop through the JSON and read all the values, however I don't think this is suitable here as some of the values might not exist (which is handled by the if let in Swift). Also, I don't think this maintains the nesting or hierarchy structure of the JSON properly, it simply visits all the values in turn.

I was reading through this tutorial: http://www.hoonzis.com/fsharp-json-serializaton/ however I'm not sure how to use :

JsonConvert.SerializeObject(data)

Am I supposed to simply create an object which mimics the structure of the JSON? How will dates get handled then, will they be converted automatically? What about doubles stored as Strings etc? I would be much more comfortable writing this code myself, like I did in Swift as this would ensure everything is properly parsed, however I do not know where to begin really and how to handle the nesting of the JSON in the code snippet I provided.

Answer 1

You can either use the JSON Type Provider , as mentioned in the comments, or you can create F# Record Types that match the structure of the JSON document you're working with and use a library like Newtonsoft.Json to deserialize the JSON to your F# records. If you specify the types in your F# record correctly, they will be parsed appropriately by the serializer, and you won't have to traverse the JSON manually. For nested objects, simply create a record type that matches the structure of the inner document and make it a field in the record for the outer object.

If you want to know how one would go about parsing JSON in F#, take a look at this tutorial .