DerivedResourceCreationConverter.cs

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using System;
using System.Diagnostics;
using AnalyzeRe.APITypes;
using AnalyzeRe.Utilities;
using Newtonsoft.Json.Linq;
 
namespace AnalyzeRe.JsonConverters
{
    public class DerivedResourceCreationConverter<T> : JsonCreationConverter<T>
        where T : IAPIType
    {
        protected override T Create(Type objectType, JObject jObject)
        {
            Type resolvedType = null;
 
            string typeName = jObject[APIType_Polymorphic.TypePropertyName]?.ToString();
            if (String.IsNullOrEmpty(typeName))
                typeName = null;
            // See if the server is specifying a polymorphic sub-type for this resource
            if (typeName != null)
            {
                TypeResolver.ResolveTypeByName(typeName, out resolvedType, typeof(T));
                // Generate a warning message if we don't recognize the server-identified type.
                if (resolvedType == null)
                {
                    if (!typeof(IAPI_Polymorphic).IsAssignableFrom(objectType))
                        Debug.WriteLine("Warning: The JSON returned from server for a " +
                            $"{objectType.NiceTypeName()} contained an unexpected type field: " +
                            $"\"{APIType_Polymorphic.TypePropertyName}\": \"{typeName}\", " +
                            "which seems unnecessary, since this class is not polymorphic. " +
                            "This could be a sign that the server added polymorphism to a class " +
                            "without making the appropriate adjustments in the C# Client Library.");
                    else
                        Debug.WriteLine("Warning: The JSON returned from server for a " +
                            $"{objectType.NiceTypeName()} contained an unrecognized value in the " +
                            $"type field: \"{APIType_Polymorphic.TypePropertyName}\": \"{typeName}\". " +
                            "This could be a sign that the server added a new sub-type to a class " +
                            "without making the appropriate adjustments in the C# Client Library.");
                }
            }
            // If the server supplied no type (or an unrecognized type), we can still
            // deserialize to the expected object type so long as it's not an abstract type.
            if (resolvedType == null && !objectType.IsAbstract && !objectType.IsInterface)
                resolvedType = objectType;
 
            // If one of the two above methods succeeded, create an object instance.
            if (resolvedType != null)
                return (T)Activator.CreateInstance(resolvedType);
            // Otherwise, prepare an error describing why we couldn't deserialize this object.
            if (typeName != null)
                throw new InvalidOperationException("JSON references an unknown " +
                    $"{objectType.NiceTypeName()} sub-type: \"{typeName}\".");
            throw new InvalidOperationException(
                "Could not create an instance of the abstract class or interface " +
                objectType.NiceTypeName() + ", and the JSON object did not contain a " +
                "_type property to determine what the correct sub-type is: " + jObject);
        }
    }
}