running a transformation on a Json DeserializeObject for a property

Question

Assuming a json string like the following:

string json = \'{\"string_property\":\"foo_bar\", ... other objects here ...}\';

I was wondering

Answer 1

I've ended up doing the following:

First, create a converter that only reads and all it does is url decode the string.

public class UrlDecoderConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(string);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;
        var s = (string)JToken.Load(reader);
        return HttpUtility.UrlDecode(s);
    }

    public override bool CanWrite => false;

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

Then, simply add the following the POCO properties that need to be decoded:

[JsonConverter(typeof(UrlDecoderConverter))]
public string url { get; set; }

Answer 2

You can transform your string properties as you deserialize your root object by using a custom JsonConverter targeted at all string type values:

public class ReplacingStringConverter : JsonConverter
{
    readonly string oldValue;
    readonly string newValue;

    public ReplacingStringConverter(string oldValue, string newValue)
    {
        if (string.IsNullOrEmpty(oldValue))
            throw new ArgumentException("string.IsNullOrEmpty(oldValue)");
        if (newValue == null)
            throw new ArgumentNullException("newValue");
        this.oldValue = oldValue;
        this.newValue = newValue;
    }

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(string);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;
        var s = (string)JToken.Load(reader);
        return s.Replace(oldValue, newValue);
    }

    public override bool CanWrite { get { return false; } }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

Then use it like:

var settings = new JsonSerializerSettings { Converters = new[] { new ReplacingStringConverter("_", "") } };
var result = JsonConvert.DeserializeObject<RootObject>(json, settings);

Note however that if individual string-type properties have their own converters applied directly with [JsonConverter(Type)], those converters will be used in preference to the ReplacingStringConverter in the Converters list.