I am failing at a task to encrypt certain fields when serializing into JSON and decrypt those fields during deserialization into a specific C# class.
I reduced the problem to its most basic issue, which is that I cannot customize the deserialization of specific fields by manipulating the value, and I don't know the reason. I am using a custom contract resolver and a custom value provider for each field. I can see that the GetValue function is executed but the SetValue is never executed.
The code sample:
class Program
{
static void Main(string[] args)
{
var text = "This is text";
var number = 1;
var anotherText = "This is another text";
var anotherNumber = 2;
var sampleInner = new SampleInner(anotherText, anotherNumber);
var sample = new SampleMessage(text, number, sampleInner);
var myCustomContractResolver = new MyCustomContractResolver();
var jsonSettings = GetJsonSettings(myCustomContractResolver);
Console.WriteLine("Serializing..");
var json = JsonConvert.SerializeObject(sample, jsonSettings);
Console.WriteLine(json);
Console.WriteLine("Deserializing..");
var sampleDeserialized = JsonConvert.DeserializeObject(json, typeof(SampleMessage), jsonSettings);
Console.WriteLine(sampleDeserialized);
Console.ReadLine();
}
private static JsonSerializerSettings GetJsonSettings(IContractResolver contractResolver)
{
var jsonSettings =
new JsonSerializerSettings
{
ContractResolver = contractResolver
};
return jsonSettings;
}
}
the custom contract resolver:
public class MyCustomContractResolver
: DefaultContractResolver
{
public MyCustomContractResolver()
{
NamingStrategy = new CamelCaseNamingStrategy();
}
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
var jsonProperties = base.CreateProperties(type, memberSerialization);
foreach (var jsonProperty in jsonProperties)
{
var propertyInfo = type.GetProperty(jsonProperty.UnderlyingName);
var defaultValueProvider = jsonProperty.ValueProvider;
jsonProperty.ValueProvider = new MyValueProvider(defaultValueProvider);
}
return jsonProperties;
}
}
and the custom value provider whose SetValue is never executed during deserialization:
public class MyValueProvider
: IValueProvider
{
private readonly IValueProvider _valueProvider;
public MyValueProvider(IValueProvider valueProvider)
{
_valueProvider = valueProvider;
}
public void SetValue(object target, object value)
{
//This is not executed during deserialization. Why?
_valueProvider.SetValue(target, value);
Console.WriteLine($"Value set: {value}");
}
public object GetValue(object target)
{
var value = _valueProvider.GetValue(target);
Console.WriteLine($"Value get: {value}");
return value;
}
}
Here is the sample code to reproduce it in case it's needed.
Hopefully somebody can let me know what am I missing :)
UPDATE 1: The object I serialize/deserialize is immutable (no public setters) and that's a requirement because I need to support such objects. As a comment points out, then it makes sense there is no SetValue executed
UPDATE 2: Thanks to @dbc for the brilliant answer no I know a good workaround for deserialization into immutable object. The final version code after the accepted answer.
UPDATE 3: The chosen answer is absolutely correct given the question. However, after investigating further I decided to go with a slightly different approach that works for both immutable and mutable classes in case somebody is in a similar situation. Instead using value providers I use now a combination of contract resolver and json converter so that with the contract resolver I can decide how to serialize/deserialize based on the type, and with the json converter I can access the value during serialization/deserialization and manipulate as desired.
Basically, on my contract resolver I override the method to create properties (where I can access my original Type properties) and selectively I specify which json converter to use.
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
var jsonProperties = base.CreateProperties(type, memberSerialization);
//Filter here based on type, attribute or whatever and if want to customize a specific property type:
foreach (var jsonProperty in jsonProperties)
{
jsonProperty.Converter = new MyJsonConverter();
}
return jsonProperties;
}
and in the MyJsonConverter we can choose what to do when writing into json or when reading from json:
public class MyJsonConverter
: JsonConverter
{
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
//I can do whatever with value
var finalValue = $"{value}-edited";
writer.WriteValue(finalValue);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
// I can do whatever with the value
var value = (string)reader.Value;
var newValue = "whatever";
return newValue;
}
public override bool CanWrite => true;
public override bool CanRead => true;
public override bool CanConvert(Type objectType)
{
return true;
}
}
