Deserialize jagged json response with unknown dimension

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Hi, I am working to deserialize a json string and write its content into a datatable. I have the following json string with jagged array and unknown dimension. Running into errors when deserialize the json into datatable.

Error: Object reference not set to an instance of an object

{
  "events": [
    {
      "Id": 456895,
      "Name": "Chelsea - Arsenal",
      "BetOffers": {
          "BetType": "Game",
          "Pick": "1",
          "Odds": 1.15
            }
    },
    {
      "Id": 456879,
      "Name": "Liverpool - Manchester United",
      "BetOffers": {
          "BetType": null,
          "Pick": "1",
          "Odds": null
            }
    },
    {
      "Id": 9101112,
      "Name": "Arsenal - Manchester United",
      "BetOffers": {
          "BetType": null,
          "Pick": "1",
          "Odds": null
            }
    },
        {
      "Id": 13141516,
      "Name": "Liverpool - Chelsea",
      "BetOffers": "not accepting"
    },
    {
      "Id": 123456,
      "Name": {
                "game": "Chelsea - Liverpool",
                "gameurl": "http://game.com/api/game/adfgfm"
            },
      "BetOffers": {
          "BetType": "Game",
          "Pick": "1",
          "Odds": 1.15
            }
    }
  ]
}

What I have tried:

I am using the below code.

C#

public class Event
{
    public int Id { get; set; }
    public string Name { get; set; }
    public BetOffer BetOffers { get; set; }
}
public class BetOffer
{
    public string BetType { get; set; }
    public string Pick { get; set; }
    public double? Odds { get; set; }
}
public class MyRootObject
{
    public List<Event> events { get; set; }
}

        try
        {
            string jsonstring = "{\"events\":[{\"Id\":456895,\"Name\":\"Chelsea - Arsenal\",\"BetOffers\":{\"BetType\":\"Game\",\"Pick\":\"1\",\"Odds\":1.15}},{\"Id\":456879,\"Name\":\"Liverpool - Manchester United\",\"BetOffers\":{\"BetType\":null,\"Pick\":\"1\",\"Odds\":null}}]}";;
            var root = JsonSerializer.Deserialize<MyRootObject>(jsonstring);

            string connectionString = "";

            DataTable dt = new DataTable();
            dt.Columns.Add(new DataColumn("ID", typeof(string)));
            dt.Columns.Add(new DataColumn("Name", typeof(string)));
            dt.Columns.Add(new DataColumn("BetType", typeof(string)));
            dt.Columns.Add(new DataColumn("Pick", typeof(string)));
            dt.Columns.Add(new DataColumn("Odds", typeof(string)));
            DataRow dr = dt.NewRow();

            for (int i = 0; i < root.events.Count; i++)
            {
                    dr = dt.NewRow();
                    dr["ID"] = root.events[i].ID;
                    dr["Name"] = root.events[i].Name;
                    dr["BetType"] = (root.events[i].BetOffers.BetType ?? (object)DBNull.Value);;
                    dr["Pick"] = root.events[i].BetOffers.Pick;
                    dr["Odds"] = (root.events[i].BetOffers.Odds ?? (object)DBNull.Value);;
                    dt.Rows.Add(dr);
            }
}

Posted 1-Dec-20 7:55am

Member 12586110

Updated 1-Dec-20 14:45pm

v4

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OriginalGriff · Answer 1 · 2020-12-01T08:17:00

Look at your code:

C#

string jsonstring;
var root = JsonSerializer.Deserialize<MyRootObject>(jsonstring);

What you pass to be deserialized contians nothing - it is null becase you have not assigned a string to the variable.

You can't deserialize nothing, that's just silly! :laugh:

Think of it this way: You have a parking space outside your house where you always park your car. If you get up one morning and leave for work but the space is empty, how are you going to drive to work?
You can't: the space contains no car.
The space is a variable: it is capable of holding a car but when it doesn't, it contains null and every time you try to use a car in an empty space you have real problems.

You need to work out where the JSON data comes from, where it is stored, and pass that to the Deserialize method - or you can't have it generate anything for you tom play with later!