Response "',' is an invalid start of a value. Path: $. in Asp.Net Core API

Question

I am developing API in Asp.Net Core 3.1, I have a POST method below (content type is application/JSON), I am passing an invalid JSON to the response deliberately and response is also very clear. But here my question is can I make changes to return the response like

countryId is a required field

for this particular case. Please let me know if it can be done, otherwise, I am fine with this response also(because this response is also valid firs to check the content type is a valid JSON or not).

Method:

public ActionResult ValidateFields(ValidateFieldsRequest validateFieldsRequest)
        {

Request class:

public class ValidateFieldsRequest
{
    //string currencyCode, int countryId, string fieldName, string fieldValue

    [Required]
    public string currencyCode { get; set; }
    [Required]
    [RegularExpression("^[1-9]\\d*$", ErrorMessage = "Invalid fieldName.")]
    public int countryId { get; set; }
    [Required]
    [MinLength(1, ErrorMessage = "At least one field required")]
    public List<Field> fields { get; set; }

}

Request:

{
    "currencyCode": "RUB",
    "countryId": ,
    "fields": [{
            "fieldName": "BIC or Bank Code",
            "fieldValue": "12345678901234567"
        },
        {
            "fieldName": "Beneficiary Account Number",
            "fieldValue": "123456"
        }
    ]
}

Response:

{
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "|6a64d7ad-495850db788356cd.",
    "errors": {
        "$.countryId": [
            "',' is an invalid start of a value. Path: $.countryId | LineNumber: 2 | BytePositionInLine: 28."
        ]
    }
}

Solution

[RegularExpression("^[1-9]\\d*$", ErrorMessage = "Invalid fieldName.")]
public int countryId { get; set; }

the error message is set above, but actually the json you are sending can not be sent like this, you should set

"countryId": null ,

Comments

[vivek nuna]

I am talking about the case, what if I am getting request like "countryId": ,

[MustafaOmar]

actually i have never saw a request from front developer without setting value of a specified field, other wise he will remove the whole field. try removing the field from your json

[vivek nuna]

Let's suppose you don't have any control on the request and client is sending you this data

[vivek nuna]

Let's suppose you don't have any control on the request and client is sending you this data

[MustafaOmar]

dear you cannot leave the "countryId" empty , you have to set a value to it

[vivek nuna]

but you have no control on client who is sending you the request, they can definitely send this request.

[MustafaOmar]

please read the "Unset property " part in here : ibm.com/support/knowledgecenter/en/SS8JB4/…

[ddfra]

then the client won't get any response but that error because the json is not properly correct. The client should at least send a json with a correct syntax.

[vivek nuna]

So according to this it should give countryid is required message

[MustafaOmar]

"then the property will not appear in the JSON data." according to this, you should remove the "countryId" or set it to null

[vivek nuna]

Dear it's the client who's sending request and I don't have any control on the request data

[MustafaOmar]

then please contact your client, and discuss with him about it