How do you add a JToken to an JObject?

Question

I'm trying to add a JSON object from some text to an existing JSON file using JSON.Net. For example if I have the JSON data as below:

  {
  "food": {
    "fruit": {
      "apple": {
        "colour": "red",
        "size": "small"
      },
      "orange": {
        "colour": "orange",
        "size": "large"
      }
    }
  }
}

I've been trying to do this like this:

var foodJsonObj = JObject.Parse(jsonText);
var bananaJson = JObject.Parse(@"{ ""banana"" : { ""colour"": ""yellow"", ""size"": ""medium""}}");
var bananaToken = bananaJson as JToken;
foodJsonObj["food"]["fruit"]["orange"].AddAfterSelf(bananaToken);

But this gives the error: "Newtonsoft.Json.Linq.JProperty cannot have multiple values."

I've actually tried a few different ways but can't seem to get anywhere. In my example what I really want to do is add the new item to "fruit". Please let me know if there is a better way of doing this or a simpler library to use.

Answer 1

I think you're getting confused about what can hold what in JSON.Net.

• A JToken is a generic representation of a JSON value of any kind. It could be a string, object, array, property, etc.
• A JProperty is a single JToken value paired with a name. It can only be added to a JObject, and its value cannot be another JProperty.
• A JObject is a collection of JProperties. It cannot hold any other kind of JToken directly.

In your code, you are attempting to add a JObject (the one containing the "banana" data) to a JProperty ("orange") which already has a value (a JObject containing {"colour":"orange","size":"large"}). As you saw, this will result in an error.

What you really want to do is add a JProperty called "banana" to the JObject which contains the other fruit JProperties. Here is the revised code:

JObject foodJsonObj = JObject.Parse(jsonText);
JObject fruits = foodJsonObj["food"]["fruit"] as JObject;
fruits.Add("banana", JObject.Parse(@"{""colour"":""yellow"",""size"":""medium""}"));

Answer 2

TL;DR: You should add a JProperty to a JObject. Simple. The index query returns a JValue, so figure out how to get the JProperty instead :)

---

The accepted answer is not answering the question as it seems. What if I want to specifically add a JProperty after a specific one? First, lets start with terminologies which really had my head worked up.

• JToken = The mother of all other types. It can be A JValue, JProperty, JArray, or JObject. This is to provide a modular design to the parsing mechanism.
• JValue = any Json value type (string, int, boolean).
• JProperty = any JValue or JContainer (see below) paired with a name (identifier). For example "name":"value".
• JContainer = The mother of all types which contain other types (JObject, JValue).
• JObject = a JContainer type that holds a collection of JProperties
• JArray = a JContainer type that holds a collection JValue or JContainer.

Now, when you query Json item using the index [], you are getting the JToken without the identifier, which might be a JContainer or a JValue (requires casting), but you cannot add anything after it, because it is only a value. You can change it itself, query more deep values, but you cannot add anything after it for example.

What you actually want to get is the property as whole, and then add another property after it as desired. For this, you use JOjbect.Property("name"), and then create another JProperty of your desire and then add it after this using AddAfterSelf method. You are done then.

For more info: http://www.newtonsoft.com/json/help/html/ModifyJson.htm

This is the code I modified.

public class Program
{
  public static void Main()
  {
    try
    {
      string jsonText = @"
      {
        ""food"": {
          ""fruit"": {
            ""apple"": {
              ""colour"": ""red"",
              ""size"": ""small""
            },
            ""orange"": {
              ""colour"": ""orange"",
              ""size"": ""large""
            }
          }
        }
      }";

      var foodJsonObj = JObject.Parse(jsonText);
      var bananaJson = JObject.Parse(@"{ ""banana"" : { ""colour"": ""yellow"", ""size"": ""medium""}}");

      var fruitJObject = foodJsonObj["food"]["fruit"] as JObject;
      fruitJObject.Property("orange").AddAfterSelf(new JProperty("banana", fruitJObject));

      Console.WriteLine(foodJsonObj.ToString());
    }
    catch (Exception ex)
    {
      Console.WriteLine(ex.GetType().Name + ": " + ex.Message);
    }
  }
}

Answer 3

Just adding .First to your bananaToken should do it:
foodJsonObj["food"]["fruit"]["orange"].Parent.AddAfterSelf(bananaToken .First);
.First basically moves past the { to make it a JProperty instead of a JToken.

@Brian Rogers, Thanks I forgot the .Parent. Edited