How to serialize a JSON property of type array to its proper .NET Array type rather than JArray

Question

I have the following JSON to POST to my Web API endpoint.

[
    {
        "name": "REGION",
        "value": ["MA", "SE", "SW"]
    }
]

The Web API endpoint is as follows

public class Parameter
{
    public string Name { get; set; }
    // Value can be string, string[], int, or int[]
    public dynamic Value { get; set; }
}

[Route("{chart}/data/")]
[HttpPost]
public IHttpActionResult GetData(string chart, IList<Parameter> parameters)
{
    // ... do stuff ...
}

Whenever value in the JSON is an array the deserialized parameter's Value is a JArray rather than an array of string, int, etc. However, if value is a simply a string or number then Value in the deserialized parameters is also a string or a number.

What gives? Why isn't the array in the JSON being deserialized into an array of the proper type?

That is how the Json.Net was designed. Value is dynamic. the framework will choose the least common denominator. Without a strongly typed object to bind to the model wont know what to convert the data to. — Nkosi, Dec 12 '18 at 22:58
This feels like an [XY problem](https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem) with a bigger issue around the design. What is this ultimately going to be used for? Why would such varying data be sent to that action? — Nkosi, Dec 12 '18 at 22:59
If you don't want `"value"` to be deserialized into `JObject` or `JArray`, you could manually convert to the conventional .Net types instead. See [How do I use JSON.NET to deserialize into nested/recursive Dictionary and List?](https://stackoverflow.com/q/5546142) and [JSON.net serializes a json array into a JArray when the destination is an object. How can I change that?](https://stackoverflow.com/q/38594282). In fact this may be a duplicate of one or both; agree? — dbc, Dec 12 '18 at 23:05
@Nkosi The endpoint accepts one or more parameters. Each parameter's value may be an int or a string. Ultimately, these are used in a where clause in SQL query to return data. Originally each parameter could have a single value. This worked well for several years. Recently, requirements changed and each parameter may have multiple values (all of the same type). — Ryan Taylor, Dec 13 '18 at 14:07

score 1 · Accepted Answer · answered Dec 13 '18 at 14:01

This was my solution. It "corrects" for JArray by inspecting the Value type after deserialization and converting it to the appropriate string[].

public class Parameter
{
    public string Name { get; set; }
    public dynamic Value { get; set; }

    [OnDeserialized]
    public void OnDeSerialized(StreamingContext context)
    {
        Type type = this.Value.GetType();
        if (type == typeof(JArray)) 
        {
            var value = (this.Value as JArray).ToObject(typeof(string[]));
            this.Value = value;
        }
    }
}

How to serialize a JSON property of type array to its proper .NET Array type rather than JArray

1 Answers1