Firebase data - error converting value

Question

I have posted question regarding firebase two days ago: Android Firebase - add authenticated user into database

I got help that I needed and that solved first problem. But now I have a new problem. I was googling for quite some time, there are some posts about this issue but nothing solved my problem. I din't want to spam the previous question so I posted a new one.

When I try reading inserted data from the firebase database I get this error:

Newtonsoft.Json.JsonSerializationException: Error converting value "test@user.com" to type 'carServiceApp.My_Classes.Account'. Path 'email', line 1, position 24.

Here is the code:

 private async Task LoadData()
    {
        FirebaseUser users = FirebaseAuth.GetInstance(loginActivity.app).CurrentUser;
        id = users.Uid;

        var firebase = new FirebaseClient(loginActivity.FirebaseURL);
        var items = await firebase.Child("users").Child(id).OnceAsync<Account>();


        foreach (var item in items)
        {
            Account user = new Account();
            user.uid = item.Object.uid;
            user.name = item.Object.name;
            user.lastName = item.Object.lastName;
            user.phone = item.Object.phone;
            user.email = item.Object.email;

            userInput_ime.Text = user.name;
            userInput_prezime.Text = user.lastName;
            userInput_broj.Text = user.phone;
            userInput_email.Text = user.email;
        }

    }

This is firebase data:

-users
    -jwAP2dYNzJeiF3QlmEIEQoruUkO2
       email: "test@user.com"
       lastName: "user"
       name: "test"
       phone: "12421"
       uid: "jwAP2dYNzJeiF3QlmEIEQoruUkO2"

Interesting thing is that when I try reading data with this:

var items = await firebase.Child("users").OnceAsync<Account>();

This works fine (I get last inserted user) . But when I add 'uid' node, then I get error. I was trying to solve this for quite some time but I just can't figure it out. I guess that there is no problem with the account class because it works in the case without uid node but doesn't work when another child() method is added.

Other information (Account class code and the way of storing that data into the database) you can see in the link at the top.

Note: I tried adding constructor in Account class but that doesn't help.

Answer 1

This was suppose to be a comment, but this is just suppose to be an addition for anyone that needs help with this issue.

I know that this answer has been out there for a while but this still seems to be a running structural quirk with Firebase and the usage of their rules. I ran into this issue with a complex structure that looked kind of like this

-Orders
    -9876trfghji (User ID)
     -0
       BusnID: "ty890oihg"
       Name: "Some Name"
       AddOns: Object
       ItemData: Object(containing other objects)
       UserID: "9876trfghji"

Note: In this case as well as the case with cordas, you will see that both of the final objects has a UserID or uid.

I also was running into the issue of class de-serialization of the object without having the actual User ID in the objects data when it was being sent back to the device.

The reason that you have a “redundant” usage of the user id is for a security measure with the Firebase rules. The first UserID with the structure above you are able to control the access to the information based off of the users id without having to have an extra validation clause in the rules. Currently as of this post the the rule below would protect the data based on the User ID.

“Orders” : {
        "$uid":{
                  ".read":"auth != null",
                  ".write":"auth.uid == $uid"
                }
    }

this allows the user with only the authorized user id to write content but anyone that has valid credentials can view the data.

The second User ID has to be placed in the object because without it you would not be able to do a standard cast to the object because your object would not have all of the data it would need to create the object. Regardless of if you are using a package like GoogleGson or Newtonsoft.Json the object still isn't full.

There is how ever a work around for this problem besides re-entering the User ID into the object. With the object that I have above I decided to just re-enter the User ID in my personal code to save the time and hassle of manual creation.

Using the Firebase.Database NuGet package you can manually create the object. Here is an example of the object in cordas problem

    public static void GetUser_Firebase(User user, FirebaseApp app)
    {
    FirebaseDatabase database = FirebaseDatabase.GetInstance(app);
    DatabaseReference reference = database.GetReference($"/users/{user.UserID}");
    //"Using for getting firebase information", $"/users/{user.UserID}"
    reference.AddListenerForSingleValueEvent(new UserInfo_DataValue());
    }

class UserInfo_DataValue : Java.Lang.Object, IValueEventListener
{
    private string ID;
 public UserInfo_DataValue(string uid)
 {
      this.ID = uid;
    }
    public void OnCancelled(DatabaseError error)
    {
        //"Failed To Get User Information For User "
    }

    public void OnDataChange(DataSnapshot snapshot)
    {
        Dictionary<string, string> Map = new Dictionary<string, string>();
        var items = snapshot.Children?.ToEnumerable<DataSnapshot>(); // using Linq
        foreach(DataSnapshot item in items)
        {
            try
            {
                Map.Add(item.Key, item.Value.ToString()); // item.value is a Java.Lang.Object
            }
            catch(Exception ex)
            {
                //"EXCEPTION WITH DICTIONARY MAP"
            }
        }
        User toReturn = new User();
        toReturn.UserID this.ID;
        foreach (var item in Map)
        {
            switch (item.Key)
            {
                case "email":
                    toReturn.email = item.Value;
                    break;
                case "lastName":
                    toReturn.lastName = item.Value;
                    break;
                case "name":
                    toReturn.name = item.Value;
                    break;
                case "phone":
                    toReturn.phone = item.Value;
                    break;                        
            }
        }
    }
}

Update There is something that I would like to mention that I left out when I was writing this and that is the usage of Firebase.Database NuGet package with the Gson NuGet package and the Newtonsoft.Json Library

If you decide to use the FIrebase.Database library just know that you will be working very close with the Java.Lang and the Java.Util libraries. Objects like Java.Lang.Object can be very difficult and time consuming to write the code needed to de-serialize the data, but don't fear Gson is here!

The Gson package if you allow it can take a large load of work off of your hands for class de-serialization if you allow it. Gson is a library that will allow you to do Java.Lang.Obj to json string de-serialization. I know it seems weird, hand it an object get back a string sounds counter intuitive I know but just bear with me.

Here is an example of how to us the Gson Library with the object in cordas problem.

 public static void Get_User(User user, FirebaseApp app)
    {
        FirebaseDatabase database = FirebaseDatabase.GetInstance(app);
        DatabaseReference reference = database.GetReference($"Users/{user.UserID}");
        reference.AddListenerForSingleValueEvent(new User_DataValue(user, app));
        //$"Trying to make call for user orders Users/{user.UserID}");
    }

class User_DataValue : Java.Lang.Object, IValueEventListener
    {
        private User User;
        private FirebaseApp app;
        public UserOrderID_Init_DataValue(User user, FirebaseApp app)
        {
            this.User = user;
            this.app = app;
        }
        public void OnCancelled(DatabaseError error)
        {
            //$"Failed To Get User Orders {error.Message}");
        }
        public void OnDataChange(DataSnapshot snapshot)
        {
            //"Data received for user orders");
            var gson = new GsonBuilder().SetPrettyPrinting().Create();

            var json = gson.ToJson(snapshot.Value); // Gson extention method obj -> string
            Formatted_Output("Data received for user order json ", json);

            User user = JsonConvert.DeserializeObject<User>(json); //Newtonsoft.Json extention method string -> object

           //now the user is a fully populated object with very little work
        }

For anyone that might run into this in the future I hope that this helps

Answer 2

Ok, so I didn't exactly find a solution for this problem nor do I really understand why was this happening but I have found a workaround. I believe it's not ideal solution and that it does not fix existing problem. Or maybe it was problem with me not understanding firebase logic but here is what I came up with.

So, considering that it was all working fine if I didn't specify that uid node it was obvious there was some problem with class and data in firebase, matching problem I guess. Anyway, I decided to have that last uid node so I can have specific user selected and also to have the same data in firebase as it was in case where it was all working. So, this is how I have inserted data into firebase:

  var item = firebase.Child("users").Child(id).PostAsync<Account>(user);

This created users node and child node. And PostAsync method created one more node with random key. So when I tried reading with this:

var data = await firebase.Child("users").Child(id).OnceAsync<Account>();

It worked without problem. Now firebase data looks like this:

   users
     JPKdQbwcXbhBatZ2ihBNLRauhV83
        -LCXyLpvdfQ448KOPKUp 
              email:  "spider@man.com"
              lastName:  "man"
              name:  "spider"
              phone:  "14412"
              uid: "JPKdQbwcXbhBatZ2ihBNLRauhV83"

There is a bit of redundancy, I basically have two ID's, but I don't understand how to create my class so I can get that data any other way so I made it this way. It works fine.

If anyone has better solution, I will gladly change it. Cheers