How Can I Detect Missing Fields During JSON Deserialization with JsonConvert?

Use JsonConvert to detect missing fields during deserialization

Handling missing fields is critical to ensuring data integrity and consistency when deserializing JSON objects using Json.NET's JsonConvert class. By default, MissingMemberHandling is set to Ignore, causing the deserializer to silently return default values ​​for missing properties. To perform strict validation and detect errors, set MissingMemberHandling to Error.

Example

Consider the following code:

<code class="language-csharp">using System;
using Newtonsoft.Json;

namespace Json_Fail_Test
{
    [JsonObject(MemberSerialization.OptOut)]
    public class MyJsonObjView
    {
        [JsonProperty("MyJsonInt")]
        public int MyJsonInt { get; set; }
    }

    class Program
    {
        const string correctData = @"{ 'MyJsonInt': 42 }";

        const string wrongData = @"{ 'SomeOtherProperty': 'fbe8c20b' }";

        static void Main()
        {
            try
            {
                JsonSerializerSettings settings = new JsonSerializerSettings()
                {
                    MissingMemberHandling = MissingMemberHandling.Error
                };

                var goodObj = JsonConvert.DeserializeObject<MyJsonObjView>(correctData, settings);
                Console.WriteLine(goodObj.MyJsonInt.ToString());

                var badObj = JsonConvert.DeserializeObject<MyJsonObjView>(wrongData, settings);
                Console.WriteLine(badObj.MyJsonInt.ToString());
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.GetType().Name + ": " + ex.Message);
            }
        }
    }
}</code>

Results

Setting MissingMemberHandling to Error will throw a JsonSerializationException when a property is missing in the JSON data.

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

Conclusion

By configuring MissingMemberHandling as Error, Json.NET enforces strict compliance with the defined class structure during deserialization. This helps identify and prevent possible data loss or corruption due to missing fields.

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