Detect if deserialized object is missing a field with the JsonConvert class in Json.NET

Question

I'm trying to deserialize some JSON objects using Json.NET. I've found however that when I deserialize an object that doesn't have the properties I'm looking for that no error is thrown up but a default value is returned for the properties when I access them. It's important that I'm able to detect when I've deserialized the wrong type of object. Example code:

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; using Newtonsoft.Json;  namespace Json_Fail_Test {     class Program     {         [JsonObject(MemberSerialization.OptOut)]         private class MyJsonObjView         {             [JsonProperty("MyJsonInt")]             public int MyJsonInt { get; set; }         }          const string correctData = @"         {             'MyJsonInt': 42         }";          const string wrongData = @"         {             'SomeOtherProperty': 'fbe8c20b'         }";          static void Main(string[] args)         {             var goodObj = JsonConvert.DeserializeObject<MyJsonObjView>(correctData);             System.Console.Out.WriteLine(goodObj.MyJsonInt.ToString());              var badObj = JsonConvert.DeserializeObject<MyJsonObjView>(wrongData);             System.Console.Out.WriteLine(badObj.MyJsonInt.ToString());         }     } } 

The output of this program is: 42 0

I would prefer an exception be thrown to failing silently. Short of that is there a way to detect if the serialization failed to find a parameter?

I know I can parse the data with a Json object and then check for the parameter with a key value lookup but the codebase I'm in uses the pattern above and I'd like keep that consistent if it's possible.

Answer 1

The Json.Net serializer has a MissingMemberHandling setting which you can set to Error. (The default is Ignore.) This will cause the serializer to throw a JsonSerializationException during deserialization whenever it encounters a JSON property for which there is no corresponding property in the target class.

static void Main(string[] args) {     try     {         JsonSerializerSettings settings = new JsonSerializerSettings();         settings.MissingMemberHandling = MissingMemberHandling.Error;          var goodObj = JsonConvert.DeserializeObject<MyJsonObjView>(correctData, settings);         System.Console.Out.WriteLine(goodObj.MyJsonInt.ToString());          var badObj = JsonConvert.DeserializeObject<MyJsonObjView>(wrongData, settings);         System.Console.Out.WriteLine(badObj.MyJsonInt.ToString());     }     catch (Exception ex)     {         Console.WriteLine(ex.GetType().Name + ": " + ex.Message);     } } 

Result:

42 JsonSerializationException: Could not find member 'SomeOtherProperty' on object of type 'MyJsonObjView'. Path 'SomeOtherProperty', line 3, position 33. 

See: MissingMemberHandling setting.