Rename JProperty in json.net

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Somewhat counterintuitively, that extension method assumes that the token you are passing to it is the value of a JProperty, not the JProperty itself. Presumably, this is to make it easy to use with the square bracket syntax:

JObject jo = JObject.Parse(json);
jo["bad"].Rename("good");

If you have a reference to the property, you can still use that extension method if you call it on the property’s Value like this:

JObject jo = JObject.Parse(json);
JProperty prop = jo.Property("bad");
prop.Value.Rename("good");

However, that makes the code seem confusing. It would be better to improve the the extension method so that it will work in both situations:

public static void Rename(this JToken token, string newName)
{
    if (token == null)
        throw new ArgumentNullException("token", "Cannot rename a null token");

    JProperty property;

    if (token.Type == JTokenType.Property)
    {
        if (token.Parent == null)
            throw new InvalidOperationException("Cannot rename a property with no parent");

        property = (JProperty)token;
    }
    else
    {
        if (token.Parent == null || token.Parent.Type != JTokenType.Property)
            throw new InvalidOperationException("This token's parent is not a JProperty; cannot rename");

        property = (JProperty)token.Parent;
    }

    // Note: to avoid triggering a clone of the existing property's value,
    // we need to save a reference to it and then null out property.Value
    // before adding the value to the new JProperty.  
    // Thanks to @dbc for the suggestion.

    var existingValue = property.Value;
    property.Value = null;
    var newProperty = new JProperty(newName, existingValue);
    property.Replace(newProperty);
}

Then you can do:

JObject jo = JObject.Parse(json);
jo.Property("bad").Rename("good");  // works with property reference
jo["good"].Rename("better");        // also works with square bracket syntax

Fiddle: https://dotnetfiddle.net/RSIdfx

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