How to add JObject property by path if not exists?

问题

Given the following code:

var context = JObject.FromObject(new
                {
                    data = new
                    {
                        mom = "",
                        dad = "",
                        sibling = "",
                        cousin = ""
                    }
                });

var path = "$.data.calculated";

var token = context.SelectToken(path);

token will be null. Thus, of course, trying this will produce an exception:

token.Replace("500");

I've seen other examples about how to add properties to a JObject, of course, but they all seem like you have to know something about the object structure beforehand. What I need to do is something like this:

if (token == null)
{
    context.Add(path);
    token = context.SelectToken(r.ContextTarget);
}

I could then use the replace method on the new token to set its' value. But context.Add(path) throws an exception:

"Can not add Newtonsoft.Json.Linq.JValue to Newtonsoft.Json.Linq.JObject."

How can I dynamically add a property using a full path like this, without knowing the existing object structure?

回答1:

While this isn't a catch-all (won't correctly do arrays for example), it does handle the above simple case and should provide for multiple levels into the hierarchy.

if (token == null)
{
    var obj = CreateObjectForPath(path, newValue);                        
    context.Merge(obj);                        
}

And the meat of the roll-your-own part:

private JObject CreateObjectForPath(string target, object newValue)
{
    var json = new StringBuilder();

    json.Append(@"{");

    var paths = target.Split('.');

    var i = -1;
    var objCount = 0;

    foreach (string path in paths)
    {
        i++;

        if (paths[i] == "$") continue;

        json.Append('"');
        json.Append(path);
        json.Append('"');
        json.Append(": ");

        if (i + 1 != paths.Length)
        {
            json.Append("{");
            objCount++;
        }
    }

    json.Append(newValue);

    for (int level = 1; level <= objCount; level++)
    {
        json.Append(@"}");
    }

    json.Append(@"}");
    var jsonString = json.ToString();
    var obj = JObject.Parse(jsonString);
    return obj;
}

来源：https://stackoverflow.com/questions/51310888/how-to-add-jobject-property-by-path-if-not-exists

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