Newtonsoft Custom Json Converter String Array to Comma Separated string WebApi 2

Question

I thought this would pretty easily to convert from JSON array to a comma-separated string and back using Newtonsoft, but I am having issues getting the ReadJson to work. I thought I would just deserialize from the reader to a string array and then call Join, but I keep getting errors: Unexpected token while deserializing object: PropertyName. Path '[0]..

Here is the code I am using:

public class myModel
{
    [JsonConverter(typeof(CommaSeperatedStringJsonConverter))]
    public string myString { get; set; }
    public int myNumber { get; set; }
}

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

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var stringArray = serializer.Deserialize(reader, typeof(string[]));
        return string.Join(",", stringArray);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        if (value is null)
        {
            writer.WriteNull();
        } 
        else
        {
            serializer.Serialize(writer, value.ToString().Split(','), typeof(string[]));
        }
    }
}

Brian Rogers · Accepted Answer · 2020-03-19 20:47:15Z

2

Try using the generic version of Deserialize instead. In other words, change this line:

var stringArray = serializer.Deserialize(reader, typeof(string[]));

To this:

var stringArray = serializer.Deserialize<string[]>(reader);

Fiddle: https://dotnetfiddle.net/KpQSiG

It shouldn't matter, but for some reason it does in this situation. If I have more time I'll try to dig into the source code to see what is happening.

edited Mar 19, 2020 at 20:47

answered Mar 19, 2020 at 20:10

Brian Rogers

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2 Comments

Calidus Over a year ago

Turns out I had a bug a different custom Json Converter being used on the same class, that was executing before this one. I am still using .Net Framework and NetwonSoft 12.03, your example looks to be using .Net Core.

Brian Rogers Over a year ago

I updated the fiddle to use .Net Framework 4.7.2 instead of .Net Core. The solution still seems to work.

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