Here are a couple of Json.NET functions which I wrote to assist in working with Json operations in C#:

public class JsonHelpers
{
	public static string MergeJsonWithStoredField(string existingJson, JProperty newJson)
	{
		if (newJson == null) throw new ArgumentNullException("newJson");

		JObject jObject;

		if (string.IsNullOrWhiteSpace(existingJson))
		{
			jObject = new JObject(newJson);
		}
		else
		{
			jObject = JObject.Parse(existingJson.Trim());
			jObject.Add(newJson);
		}

		return jObject.ToString(Formatting.None);
	}


	public static IEnumerable<JProperty> CreateJsonPropertiesFromObject(Object objectToJsonify)
	{
		if (objectToJsonify == null) throw new ArgumentNullException("objectToJsonify");

		ICollection<JProperty> properties = new List<JProperty>();

		foreach (var propertyInfo in objectToJsonify.GetType().GetProperties(BindingFlags.Instance | BindingFlags.Public))
		{
			properties.Add(new JProperty(propertyInfo.Name, propertyInfo.GetValue(objectToJsonify)));
		}

		return properties;
	}

	public static string AddObjectToJsonArray(string jsonAsString, string keyOfArray, Object objectToJsonify)
	{
		JObject existingStoredJsonObject;
		JArray jArray;

		// convert object to a json object
		var newJsonObject = new JObject(CreateJsonPropertiesFromObject(objectToJsonify));

		// if the existing stored string is null or emptiness, just create it and return.
		if (string.IsNullOrWhiteSpace(jsonAsString))
		{
			existingStoredJsonObject = new JObject();
			jArray = new JArray(newJsonObject);
			existingStoredJsonObject.Add(JsonPropertyKeys.PostEventMaterialsWereAccessed, jArray);

			return existingStoredJsonObject.ToString(Formatting.None);
		}

		// ************* if we got here, we need to now process the existing stored json as an input *************
		existingStoredJsonObject = JObject.Parse(jsonAsString);

		// 1st, see if valid json is stored at all
		if (!ReferenceEquals(null, existingStoredJsonObject))
		{
			JToken jToken;

			// 2nd, see if the array which we are augmenting already exists
			if (existingStoredJsonObject.TryGetValue(keyOfArray, StringComparison.OrdinalIgnoreCase, out jToken))
			{
				jArray = jToken.Value<JArray>();
				jArray.AddFirst(newJsonObject); // add so most recent is at beginning of the array

				return existingStoredJsonObject.ToString(Formatting.None);
			}

			// if the array does not exist in the existing json, just create it
			jArray = new JArray(newJsonObject);
			existingStoredJsonObject.Add(keyOfArray, jArray);

			return existingStoredJsonObject.ToString(Formatting.None);
		}

		return jsonAsString;
	}

	public static JObject CreateJsonObjectFromDictionary(IDictionary<string, string> dataForJson)
	{
		var outObject = new JObject();

		foreach (var keyValuePair in dataForJson)
		{
			outObject.Add(keyValuePair.Key, keyValuePair.Value);
		}

		return outObject;
	}
}

The methods came in handy as I was storing json in a database field of type nvarchar. I needed to be able to update the json, add new keys/values and augment existing arrays.

Here’s a few usage examples:

1. Adds a new property to an existing Json object:

public static AugmentOrderHistory(SomeViewModel viewModel, bool? createdByImpersonatedClaim)
{
	...
	JProperty createdByImpersonatedUserMsg = new JProperty(
		JsonPropertyKeys.OrderCreatedByImpersonatedUserKey,
		createdByImpersonatedClaim.Value
		);

	newOrder.AdminComments = JsonHelpers.MergeJsonWithStoredField(
		newOrder.AdminComments, 
		createdByImpersonatedUserMsg
		);
	...
}

2. Converts a C# object to a JObject and adds it as a Json object to a Javascript array.

 
public static AugmentOrderHistoryWithObject(...)
{
	...
	var fieldsToComments = new PostEventMaterialsWereAccessed
	{
		DateAdded = TtsConfig.UtcNowAsCts,
		Code = identifyModel.OnDemandCode,
		UserEmail = identifyModel.Email,
		UserName = identifyModel.FullName,		
	};	
	
	string updatedUserComments = JsonHelpers.AddObjectToJsonArray(
		order.History,
		JsonPropertyKeys.PostEventMaterialsWereAccessedKey,
		fieldsToComments
		);
	...
        /* json looks something like {"PostEventMaterialsWereAccessed":[{"Code":"rzszq","DateAdded":"2015-06-03T06:49:34.0986495","UserName":"Jonty","UserEmail":"jonty@bla.com"},{"Code":"rzszq","DateAdded":"2015-06-02T14:52:56.7051448","UserName":"harry","UserEmail":"harry@bla.com"}]} */
}

New Zealand should declare James Newton-King to be a nationl treasure.