Json.Net can't deserialize from dynamic object to nullable<short>

Question

I have the following JSON being sent to an MVC controller:

{
  "CId": 374,
  "CultureId": 1,
  "VGS": null,
  "DisplayOrder": 1
}

I am using JSON.Net to convert this to a dynamic object and later assigning the properties into an entity:

public partial class FooEntity
{
    public short DisplayOrder { get; set; }
    public Nullable<short> VGS { get; set; }
    public short CId { get; set; }
    public short CultureId { get; set; }
}

Notice that the VGS property we are assigning into is a nullable short, however when trying to create a new instance of the entity and assign the values, I get an error when trying to assign the VGS:

dynamic data = JsonConvert.DeserializeObject(payload);
var foo = new FooEntity();
foo.CId = data.CId;
foo.CultureId = data.CultureId;
foo.VGS = data.VGS; // Errors here
foo.DisplayOrder = data.DisplayOrder;

An exception of type 'System.FormatException' occurred in mscorlib.dll but was not handled in user code

Additional information: Input string was not in a correct format.

As far as I can tell, the json is correct to deserialize into a null value, and since I am assigning into a nullable value, I'm not sure what is causing the error?

Maybe VGS is being deserialized as object, and that's why you can't assign it to a Nullable<sort> — Pikoh
– Pikoh, Commented Jan 18, 2017 at 10:22
JsonConvert.DeserializeObject<FooEntity>(payload);Can you try with generic? — Hameed Syed
– Hameed Syed, Commented Jan 18, 2017 at 10:22

smoksnes · Accepted Answer · 2017-01-18 10:33:02Z

1

JSON.Net does not know what to parse VGS to, which will make it an object. Then you cannot assign an object to VGS. Below is a working example. It can be solved in several ways:

Solution 1: Use explicit cast.

var payload = "{\"CId\": 374, \"CultureId\": 1,\"VGS\": null,\"DisplayOrder\": 1}";
dynamic dyn = JsonConvert.DeserializeObject<FooEntity>(payload);
var foo2 = new FooEntity();
foo.CId = dyn.CId;
foo.CultureId = dyn.CultureId;
foo.VGS = (short?)dyn.VGS; // Note the explicit cast.
foo.DisplayOrder = dyn.DisplayOrder;

Solution 2: Specify type.

var payload = "{\"CId\": 374, \"CultureId\": 1,\"VGS\": null,\"DisplayOrder\": 1}";
dynamic data = JsonConvert.DeserializeObject<FooEntity>(payload); // Specify type.
var foo = new FooEntity();
foo.CId = data.CId;
foo.CultureId = data.CultureId;
foo.VGS = data.VGS;
foo.DisplayOrder = data.DisplayOrder;

But then there's really no reason to use dynamic at all. You can serialize it directly to the entity you want.

FooEntity entity = JsonConvert.DeserializeObject<FooEntity>(payload);

answered Jan 18, 2017 at 10:33

smoksnes

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3 Comments

Anduril Over a year ago

Solution 2 wasnt possible because the actual payload is more complicated but solution 1 worked. Thank you.

Ghasan غسان Over a year ago

The first solution does not really solve the issue, even if you don't specify a cast, it works fine. Netwtonsft.Json has implicit conversion operators to and from most built-in types, and this is not an issue. The issue here is something else, but hopefully the second one worked for the OP.

Ghasan غسان Over a year ago

You can see here that JToken has almost all implicit conversions to built-in types. github.com/JamesNK/Newtonsoft.Json/blob/…

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