error while de-serializing string with escape characters in it

Question

I hope it is something very simple and must be a common scenario for other devs.

I'm sending an OUT variable from SQL which contains the error details. In my DataLayer API, I check it in VS Debugger and that's how it appears:

var string_from_stored_proc = "[{\"errornumber\":2627,\"errormessage\":\"Violation of UNIQUE KEY constraint 'KEY_Subject'. Cannot insert duplicate key in object 'edu.Subject'. The duplicate key value is (MATS10, 2).\",\"errorstate\":1,\"errorseverity\":14,\"errorline\":36,\"errroprocedure\":\"SPCreateSubject\",\"xactstate\":1}]"

I understand that VS debugger adds the escape () to the string. When I try to deserialize this string using:

JsonConvert.DeserializeObject<my_error_object>(string_from_stored_proc);

I get this error:

{"Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'BaaS.DTO.SQLErrorHandler' because the type requires a JSON object (e.g. {\"name\":\"value\"}) to deserialize correctly.\r\nTo fix this error either change the JSON to a JSON object (e.g. {\"name\":\"value\"}) or change the deserialized type to an array or a type that implements a collection interface (e.g. ICollection, IList) like List that can be deserialized from a JSON array. JsonArrayAttribute can also be added to the type to force it to deserialize from a JSON array.\r\nPath '', line 1, position 1."}

json2csharp.com fails to convert this JSON. If I remove all backslashes, it does the job. Below is the my_error_object (or converted by json2sharp) Class:

public class my_error_object
{
    public int errornumber { get; set; }
    public string errormessage { get; set; }
    public int errorstate { get; set; }
    public int errorseverity { get; set; }
    public int errorline { get; set; }
    public string errroprocedure { get; set; }
    public int xactstate { get; set; }
}

I tried to process the string_from_stored_proc and remove all backslashes but I can't remove the escape chars (which I think is the expected behavior). With those slashes, I'm unable to get the string deserialized.

Workaround: If I use var outputJson = Newtonsoft.Json.Linq.JToken.Parse(string_from_stored_proc); , it gives an output the below output:

{[
  {
    "errornumber": 2627,
    "errormessage": "Violation of UNIQUE KEY constraint 'KEY_Subject'. Cannot insert duplicate key in object 'edu.Subject'. The duplicate key value is (MATS10, 2).",
    "errorstate": 1,
    "errorseverity": 14,
    "errorline": 36,
    "errroprocedure": "SPCreateSubject",
    "xactstate": 1
  }
]}

Upon removing starting and trailing braces, am able to deserialize using NewtonSoft.

However, when I send it from the DataLayer using BadRequest(deserialized_string_from_stored_proc) and retrieve it in the BusinessLayer using

var output = await response.Content.ReadAsAsync<SQLErrorHandler>();

The output variable again has a lot of extra chars which I then need to process again. The only way which works for me is to send the deserialized object using HttpResults.OK(object) and the read it in my BusinessLayer. Which I don't want to do since it is not the correct return type in case of error.

Am I doing it right? I have two questions:

Is there a way to deserialize the given string and send over using to the BusinessLayer without string processing it?
If first is not possible, could I simply pass the string to the BusinessLayer and deserialize it there (preferred way)?

I'm happy to provide more info or code snippet to reproduce the error.

EDIT: per @Equalsk's suggestion, I have been able to deserialize it properly. however, it's in the Datalayer at the moment. Here is the output:

var equalskObj = JsonConvert.DeserializeObject<List<SQLErrorHandler>>(outputFromSP.Value.ToString());
return Ok(equalskObj);

However, I'm still not able to do the preferred way (#2). If I send the string to the BusinessLayer using return BadRequest(string_from_stored_proc) it sends

"{\r\n \"message\": \"[{\\"errornumber\\":2627,\\"errormessage\\":\\"Violation of UNIQUE KEY constraint 'KEY_Subject'. Cannot insert duplicate key in object 'edu.Subject'. The duplicate key value is (MATS10, 2).\\",\\"errorstate\\":1,\\"errorseverity\\":14,\\"errorline\\":36,\\"errroprocedure\\":\\"SPCreateSubject\\",\\"xactstate\\":1}]\"\r\n}"

Where I still have to process it. Is there a cleaner way of sending it over and then to convert as suggested? I think I should post a simplified question for this since these are separate issues. I'm really interested to see what's the best approach to do it.

Have you tried JsonConvert.DeserializeObject<List<my_error_object>>(string_from_stored_proc);? — Equalsk
– Equalsk, Commented Feb 28, 2017 at 20:53
It's looking for a list/array type because your SQL string has [ and ] around its contents. Remove those, then deserialize. — Heretic Monkey
– Heretic Monkey, Commented Feb 28, 2017 at 20:57
@Equalsk - Thanks a bunch. It did the trick. I somehow ignored that it was returning a list even when the return variable set in the Stored Procedure is a varchar (string in C# model). — sandiejat
– sandiejat, Commented Mar 1, 2017 at 0:44
However, I'm still stuck with return Ok(object) instead of being able to send a clean error string using BadRequest(string_from_stored_proc) and deserialize it in the BusinessLayer. I have updated the question with the output. Thanks again. @MikeMcCaughan - Though your answer works, it is not something I want to do in first place since it involves manual string processing. — sandiejat
– sandiejat, Commented Mar 1, 2017 at 0:50

raga · Accepted Answer · 2017-03-20 01:50:21Z

2

I was stuck with a similar thing. To get the output from your DL, you can return as below:

FROM DL (Called/Second) API

return Content(<HttpStatusCode>, "Custom Error Message Here");

For example:

Return Content(System.Net.HttpStatusCode.BadRequest, e.Message.ToString());

now in BL (First/Calling) API, if the StatusCode is not Success then read the response result. Like this:

if(!response.IsSuccessStatusCode)
{
    var errorOutput = response.Content.ReadAsStringAsync().Result;
    //Now send this errorOutput from this API to the client. Return an HTTPResult or another Content from here. Upto you!
}
return Ok(); //If response.statuscode is Success

answered Mar 20, 2017 at 1:50

raga

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1 Comment

sandiejat Over a year ago

that's helpful. passing Content is better as it supports custom error/message along with the Status Code.

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