I would like to deserialize a System.Security.Claims.Claim
object serialized in the following way:
{
"Issuer" : "LOCAL AUTHORITY",
"OriginalIssuer" : "LOCAL AUTHORITY",
"Type" : "http://my.org/ws/2015/01/identity/claims/mytype",
"Value" : "myvalue",
"ValueType" : "http://www.w3.org/2001/XMLSchema#string"
}
What I get is a JsonSerializationException
:
Unable to find a constructor to use for type System.Security.Claims.Claim. A class should either have a default constructor, one constructor with arguments or a constructor marked with the JsonConstructor attribute.
After some investigation I finally understand the meaning of one in the above message: The JSON deserializer cannot find the right constructor as there are - in the case of the Claim
type - multiple constructors with arguments (although there exists a constructor with arguments matching exactly the above properties).
Is there a way to tell the deserializer which constructor to choose without adding the JsonConstructor
attribute to that mscorlib type?
Daniel Halan has solved this issue with a patch to Json.NET a few years ago. Is there a way to solve this without modifying Json.NET these days?
If it is not possible to add a [JsonConstructor]
attribute to the target class (because you don't own the code), then the usual workaround is to create a custom JsonConverter
as was suggested by @James Thorpe in the comments. It is pretty straightforward. You can load the JSON into a JObject
, then pick the individual properties out of it to instantiate your Claim
instance. Here is the code you would need:
class ClaimConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(System.Security.Claims.Claim));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JObject jo = JObject.Load(reader);
string type = (string)jo["Type"];
string value = (string)jo["Value"];
string valueType = (string)jo["ValueType"];
string issuer = (string)jo["Issuer"];
string originalIssuer = (string)jo["OriginalIssuer"];
return new Claim(type, value, valueType, issuer, originalIssuer);
}
public override bool CanWrite
{
get { return false; }
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
To use the converter, simply pass an instance of it to the JsonConvert.DeserializeObject<T>()
method call:
Claim claim = JsonConvert.DeserializeObject<Claim>(json, new ClaimConverter());
Fiddle: https://dotnetfiddle.net/7LjgGR