System.Text.Json - The JSON value could not be converted to System.String

Question

I have the following json being sent to api

{
     "Id":22,
     "UserId":22,
     "Payload":{
        "Field":"some payload value"
        ...more unknown field/values go here
     },
     "ContextTypeId":1,
     "EventTypeId":1,
     "SessionId":1
}

I would like to map it to the following:

  public class CreateTrackItem : IRequest<int>
    {  
        public int Id { get; set; }
        public int UserId { get; set; }

        public string Payload { get; set; }
        public int ContextTypeId { get; set; }
        public int SessionId { get; set; }
        public int EventTypeId { get; set; }
    }

When mapped the Payload property fails that it cannot map json to string, i simply want the Payload to be a string version of the json (will go into a jsonb field in postgres)

I am using .NET Core 3.0 and prefer to use the built in System.Text.Json if possible before switching to Newtonsoft.

`Payload` needs to be a `class` object with `property` `Field`. `"Payload":{ "Field":"some payload value" },` This is a complex object, not a string. — Ryan Wilson, Oct 29 '19 at 20:20
@RyanWilson since the payload structure is unknown, other than that it will be valid json, its impossible to construct a class, that is why the property is set to be a string which will take what ever json is thrown at it — Zoinky, Oct 29 '19 at 20:25
Then you either need to write a custom `JSON Converter` or try using type `JToken`, please see this post (https://stackoverflow.com/questions/29980580/deserialize-json-object-property-to-string) — Ryan Wilson, Oct 29 '19 at 20:26

score 9 · Answer 1 · edited Mar 07 '22 at 00:48

9

If you are using asp.net core 3.0 (or System.Text.Json with .Net 6) then this has built-in JSON support. I have used the following and it works without setting the custom input handler.

//// using System.Text.Json;

[HttpPost]
public async Task<IActionResult> Index([FromBody] JsonElement body)
{

    string json = System.Text.Json.JsonSerializer.Serialize(body);
    return Ok();

}

edited Mar 07 '22 at 00:48

Jeremy Thompson

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answered Nov 24 '19 at 03:28

ameya

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score 0 · Accepted Answer · answered Oct 29 '19 at 21:01

You can use Object type instead of string. Or use JToken type from Newtonsoft as Ryan already commented above.

public object Payload { get; set; }

 public class CreateTrackItem : IRequest<int>
{  
    public int Id { get; set; }
    public int UserId { get; set; }

    public object Payload { get; set; }
    public int ContextTypeId { get; set; }
    public int SessionId { get; set; }
    public int EventTypeId { get; set; }
}

System.Text.Json - The JSON value could not be converted to System.String

2 Answers2