How can I deserialize JSON to a simple Dictionary in ASP.NET?

Question

I have a simple key/value list in JSON being sent back to ASP.NET via POST. Example:

{ \"key1\": \"value1\", \"key2\": \"value2\"}

Answer 1

It seems all of these answers here just assume you can get that little string out of a bigger object... for people looking to simply deserealize a large object with such a dictionary somewhere inside the mapping, and who are using the System.Runtime.Serialization.Json DataContract system, here's a solution:

An answer on gis.stackexchange.com had this interesting link. I had to recover it with archive.org, but it offers a pretty much perfect solution: a custom IDataContractSurrogate class in which you implement exactly your own types. I was able to expand it easily.

I made a bunch of changes in it, though. Since the original source is no longer available, I'll post the entire class here:

using System;
using System.CodeDom;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Json;
using System.Text;

namespace JsonTools
{
    /// 

    /// Allows using Dictionary<String,String> and Dictionary<String,Boolean> types, and any others you'd like to add.
    /// Source: https://web.archive.org/web/20100317222656/my6solutions.com/post/2009/06/30/DataContractSerializer-DataContractJsonSerializer-JavaScriptSerializer-XmlSerializer-for-serialization.aspx
    /// 
    public class JsonSurrogate : IDataContractSurrogate
    {
        /// 

        /// Deserialize an object with added support for the types defined in this class.
        /// 
        /// Contract class
        /// JSON String
        /// Text encoding
        /// The deserialized object of type T
        public static T Deserialize(String json, Encoding encoding)
        {
            if (encoding == null)
                encoding = new UTF8Encoding(false);
            DataContractJsonSerializer deserializer = new DataContractJsonSerializer(
                typeof(T), new Type[0], int.MaxValue, true, new JsonSurrogate(), false);
            using (MemoryStream stream = new MemoryStream(encoding.GetBytes(json)))
            {
                T result = (T)deserializer.ReadObject(stream);
                return result;
            }
        }

        // make sure all values in this are classes implementing JsonSurrogateObject.
        private static Dictionary KnownTypes = 
            new Dictionary()
            {
                {typeof(Dictionary), typeof(SSDictionary)},
                {typeof(Dictionary), typeof(SBDictionary)}
            };

        #region Implemented surrogate dictionary classes

        [Serializable]
        public class SSDictionary : SurrogateDictionary
        {
            public SSDictionary() : base() {}
            protected SSDictionary (SerializationInfo info, StreamingContext context) : base(info, context) {}
        }
        [Serializable]
        public class SBDictionary : SurrogateDictionary
        {
            public SBDictionary() : base() {}
            protected SBDictionary (SerializationInfo info, StreamingContext context) : base(info, context) {}
        }

        #endregion

        /// 
Small interface to easily extract the final value from the object.
        public interface JsonSurrogateObject
        {
            Object DeserializedObject { get; }
        }

        /// 

        /// Class for deserializing any simple dictionary types with a string as key.
        /// 
        /// Any simple type that will be deserialized correctly.
            [Serializable]
        public abstract class SurrogateDictionary : ISerializable, JsonSurrogateObject
        {
            public Object DeserializedObject { get { return dict; } }
            private Dictionary dict;

            public SurrogateDictionary()
            {
                dict = new Dictionary();
            }

            // deserialize
            protected SurrogateDictionary(SerializationInfo info, StreamingContext context)
            {
                dict = new Dictionary();
                foreach (SerializationEntry entry in info)
                {
                    // This cast will only work for base types, of course.
                    dict.Add(entry.Name, (T)entry.Value);
                }
            }
            // serialize
            public void GetObjectData(SerializationInfo info, StreamingContext context)
            {
                foreach (String key in dict.Keys)
                {
                    info.AddValue(key, dict[key]);
                }
            }

        }

        /// 

            /// Uses the KnownTypes dictionary to get the surrogate classes.
        /// 
        /// 
        /// 
        public Type GetDataContractType(Type type)
        {
            Type returnType;
            if (KnownTypes.TryGetValue(type, out returnType))
            {
                return returnType;
            }
            return type;
        }

        public object GetObjectToSerialize(object obj, Type targetType)
        {
            throw new NotImplementedException();
        }

        /// 

        ///     Gets the object out of the surrogate datacontract object. This function is the reason all surrogate objects need to implement the JsonSurrogateObject class.
        /// 
        /// Result of the deserialization
        /// Expected target type of the deserialization
        /// 
        public object GetDeserializedObject(object obj, Type targetType)
        {
            if (obj is JsonSurrogateObject)
            {
                return ((JsonSurrogateObject)obj).DeserializedObject;
            }
            return obj;
        }

        public Type GetReferencedTypeOnImport(string typeName, string typeNamespace, object customData)
        {
            return null;
        }

        #region not implemented

        public object GetCustomDataToExport(MemberInfo memberInfo, Type dataContractType)
        {
            throw new NotImplementedException();
        }

        public object GetCustomDataToExport(Type clrType, Type dataContractType)
        {
            throw new NotImplementedException();
        }

        public void GetKnownCustomDataTypes(Collection customDataTypes)
        {
            throw new NotImplementedException();
        }

        public CodeTypeDeclaration ProcessImportedType(CodeTypeDeclaration typeDeclaration, CodeCompileUnit compileUnit)
        {
            throw new NotImplementedException();
        }

        #endregion
    }
}

To add new supported types to the class, you just need to add your class, give it the right constructors and functions (look at SurrogateDictionary for an example), make sure it inherits JsonSurrogateObject, and add its type mapping to the KnownTypes dictionary. The included SurrogateDictionary can serve as basis for any Dictionary types where T is any type that does deserialize correctly.

Calling it is really simple:

MyObjtype newObj = JsonSurrogate.Deserialize(jsonStr, encoding);

Note that for some reason this thing has trouble using key strings which contain spaces; they were simply not present in the final list. Might just be it's simply against json specs and the api I was calling was poorly implemented, mind you; I dunno. Anyway, I solved this by regex-replacing them with underscores in the raw json data and fixing the dictionary after the deserialization.