C#, Json deserialization: avoid empty string array elements

Question

My json array, which comes to me from the server, can contain empty string elements. I want to remove them at the level of deserialization.

{
   "Highlights":[
         "Þingvellir National Park",
         "Gullfoss Waterfall",
         "Geysir Geothermal Area",
         "Laugarvatn","Kerið Crater",
         "Hveragerði Hot Spring Area",
         "",
         ""
   ]
}

Model:

public class TestModel
{
    public List<string> Highlights { get; set; }
}

I want that if the element is string.IsNullOrEmpty (element) == true, then it is not added to the array.

In this case, the number of elements after deserialization in the TestModel.Highlights array should be 6, not 8, because 2 of them are empty.

How can I achieve this?

Any reason you can't just run through the list afterwards and remove null or empty elements? That's likely to be simpler than persuading whatever JSON parser you're using to do it on the fly. — Jon Skeet
– Jon Skeet, Commented Nov 6, 2018 at 18:27
There is no reason or benefit to doing this, just do a simple Linq Where(s => !string.IsNullOrEmpty(s)) on Highlights — maccettura
– maccettura, Commented Nov 6, 2018 at 18:35
implementing your own JsonConverter would be probably very YAGNI :) — Falco Alexander
– Falco Alexander, Commented Nov 6, 2018 at 19:24

LeviTheOne · Accepted Answer · 2018-11-06 19:25:08Z

The simple way is to iterate trough the collection and check for null or empty strings as suggested in comments. The harder and ugly(for this situation) way would be to create a custom JsonConverter based on this answer like:

class IgnoreEmptyItemsConverter<T> : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType.IsAssignableFrom(typeof(List<T>));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        List<T> list = new List<T>();
        JArray array = JArray.Load(reader);
        foreach (var obj in array)
        {
            // really custom way (not really generic)
            if (!String.IsNullOrEmpty(obj.ToString()))
            {
                list.Add(obj.ToObject<T>(serializer));
            }
        }
        return list;
    }

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

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

and this can be used in your model like:

public class RootObject
{
    [JsonConverter(typeof(IgnoreEmptyItemsConverter<string>))]
    public List<string> Highlights { get; set; }
}

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