Remove fields from JSON dynamically using Json.Net

Question

I have some JSON input, the shape of which I cannot predict, and I have to make some transformations (to call it something) so that some fields are not logged. For instance,

Answer 1

You can parse your JSON to a JContainer (which is either an object or array), then search the JSON hierarchy using DescendantsAndSelf() for properties with names that match some Regex, or string values that match a Regex, and remove those items with JToken.Remove().

For instance, given the following JSON:

{
  "Items": [
    {
      "id": 5,
      "name": "Peter",
      "password": "some pwd"
    },
    {
      "id": 5,
      "name": "Peter",
      "password": "some pwd"
    }
  ],
  "RootPasswrd2": "some pwd",
  "SecretData": "This data is secret",
  "StringArray": [
    "I am public",
    "This is also secret"
  ]
}

You can remove all properties whose name includes "pass.*w.*r.*d" as follows:

var root = (JContainer)JToken.Parse(jsonString);

var nameRegex = new Regex(".*pass.*w.*r.*d.*", RegexOptions.IgnoreCase | RegexOptions.CultureInvariant);
var query = root.DescendantsAndSelf()
    .OfType()
    .Where(p => nameRegex.IsMatch(p.Name));
query.RemoveFromLowestPossibleParents();

Which results in:

{
  "Items": [
    {
      "id": 5,
      "name": "Peter"
    },
    {
      "id": 5,
      "name": "Peter"
    }
  ],
  "SecretData": "This data is secret",
  "StringArray": [
    "I am public",
    "This is also secret"
  ]
}

And you can remove all string values that include the substring secret by doing:

var valueRegex = new Regex(".*secret.*", RegexOptions.IgnoreCase);
var query2 = root.DescendantsAndSelf()
    .OfType()
    .Where(v => v.Type == JTokenType.String && valueRegex.IsMatch((string)v));
query2.RemoveFromLowestPossibleParents();

var finalJsonString = root.ToString();

Which when applied after the first transform results in:

{
  "Items": [
    {
      "id": 5,
      "name": "Peter"
    },
    {
      "id": 5,
      "name": "Peter"
    }
  ],
  "StringArray": [
    "I am public"
  ]
}

For convenience, I am using the following extension methods:

public static partial class JsonExtensions
{
    public static TJToken RemoveFromLowestPossibleParent(this TJToken node) where TJToken : JToken
    {
        if (node == null)
            return null;
        JToken toRemove;
        var property = node.Parent as JProperty;
        if (property != null)
        {
            // Also detach the node from its immediate containing property -- Remove() does not do this even though it seems like it should
            toRemove = property;
            property.Value = null;
        }
        else
        {
            toRemove = node;
        }
        if (toRemove.Parent != null)
            toRemove.Remove();
        return node;
    }

    public static IEnumerable RemoveFromLowestPossibleParents(this IEnumerable nodes) where TJToken : JToken
    {
        var list = nodes.ToList();
        foreach (var node in list)
            node.RemoveFromLowestPossibleParent();
        return list;
    }
}

Demo fiddle here.