Deserializing JSON when sometimes array and sometimes object

A very detailed explanation on how to handle this case is available at “Using a Custom JsonConverter to fix bad JSON results”.

To summarize, you can extend the default JSON.NET converter doing

1. Annotate the property with the issue

   [JsonConverter(typeof(SingleValueArrayConverter<OrderItem>))]
   public List<OrderItem> items;
   

2. Extend the converter to return a list of your desired type even for a single object

   public class SingleValueArrayConverter<T> : JsonConverter
   {
       public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
       {
           throw new NotImplementedException();
       }
   
       public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
       {
           object retVal = new Object();
           if (reader.TokenType == JsonToken.StartObject)
           {
               T instance = (T)serializer.Deserialize(reader, typeof(T));
               retVal = new List<T>() { instance };
           } else if (reader.TokenType == JsonToken.StartArray) {
               retVal = serializer.Deserialize(reader, objectType);
           }
           return retVal;
       }
   
       public override bool CanConvert(Type objectType)
       {
           return true;
       }
   }
   

As mentioned in the article this extension is not completely general but it works if you are fine with getting a list.