How to Efficiently Locate JTokens by Name within Nested JObject Hierarchies?

Locating JTokens by Name in JObject Hierarchies

In response to the need for retrieving specific JTokens from complex JSON responses, this article presents a discussion on the available options within the NewtonsoftJson library and provides an alternative solution in the form of a recursive method.

NewtonsoftJson SelectToken Method

While the NewtonsoftJson library does not offer a direct method for searching JTokens by name, it does provide the SelectToken() method. This method allows you to navigate through the JObject hierarchy and select tokens based on their path. For instance, to retrieve the "text" JToken from the provided JSON response:

JObject jObject = JObject.Parse(json);
string distanceText = jObject.SelectToken("routes[0].legs[0].distance.text").ToString();

Recursive Token Search Method

If you require finding all occurrences of a JToken with a specific name regardless of its location, a recursive method is necessary. Here's an example:

public static class JsonExtensions
{
    public static List<jtoken> FindTokens(this JToken containerToken, string name)
    {
        // Initialize a list to store matching JTokens
        List<jtoken> matches = new List<jtoken>();

        // Call the recursive helper method
        FindTokens(containerToken, name, matches);

        // Return the matches
        return matches;
    }

    private static void FindTokens(JToken containerToken, string name, List<jtoken> matches)
    {
        // Recursively traverse the JObject and JArray elements
        switch (containerToken.Type)
        {
            case JTokenType.Object:
                // Check JProperties for the name and recurse on their values
                foreach (JProperty child in containerToken.Children<jproperty>())
                {
                    if (child.Name == name)
                    {
                        matches.Add(child.Value);
                    }
                    FindTokens(child.Value, name, matches);
                }
                break;
            case JTokenType.Array:
                // Recurse on each element of the array
                foreach (JToken child in containerToken.Children())
                {
                    FindTokens(child, name, matches);
                }
                break;
        }
    }
}</jproperty></jtoken></jtoken></jtoken></jtoken>

Demo and Output

Here's a sample demonstration:

// Load the JSON response
string json = GetJson();

// Parse the JSON into a JObject
JObject jo = JObject.Parse(json);

// Find all "text" JTokens using the FindTokens method
foreach (JToken token in jo.FindTokens("text"))
{
    Console.WriteLine(token.Path + ": " + token.ToString());
}

This code prints the following output:

routes[0].legs[0].distance.text: 1.7 km
routes[0].legs[0].duration.text: 4 mins
routes[0].legs[1].distance.text: 2.3 km
routes[0].legs[1].duration.text: 5 mins

Conclusion

While the built-in SelectToken() method provides a convenient way to navigate specific paths in a JObject, the recursive FindTokens method offers a solution for finding all occurrences of a JToken with a given name, regardless of its location within the hierarchy. The choice between these approaches depends on the specific requirements of your application.

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