Model Binding returns null model - asp.net-core

Question

I have been unable to resolve an issue with Model Binding in an action.
It DOES bind, but not all of the time. Sometimes, the value is null and so of course it throws an error.
It seems to happen about 50% of the time, sometimes after the user has been logged in for a 4 minutes or longer.
This is the action:
[HttpPost]
public IActionResult Post([FromBody]Csr csr)
{
try
{
if(csr == null)
{
throw new Exception("Associate Controller recieved csr parameter when posting a new CSR");
}
//csr.ParentCsrId = this.GetCurrentCsr().CsrId;
csr.InsertedDate = DateTime.Now;
csr.UpdatedDate = DateTime.Now;
return Ok(_associateRepository.Add(csr));
}
catch (Exception ex)
{
LogException(ex, "Associate Controller", "Post([FromBody]Csr csr)");
throw ex;
}
}
The exception is thrown and logged correctly.
This is the data that was posted according to the browser:
Headers:
POST /api/associate HTTP/1.1
Host: portal.5-15globalenergy.it
Connection: keep-alive
Content-Length: 557
Accept: application/json
Origin: https://portal.5-15globalenergy.it
Authorization: Bearer xxxzy User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.36
Content-Type: application/json
Referer: https://portal.5-15globalenergy.it/
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
Body:
{"csrTypeId":1,"countryId":2,"stateCode":"SO","birthCountryId":2,"birthStateCode":"SO","city":"Sondrio","streetPart":"STAZIONE","birthCity":"Sondrio","firstName":"Test","lastName":"User","maritalStatusId":2,"citizenshipCountryId":2,"personalTaxNum":"xxxxxx","streetName":"VIA SAN GOTTARDO","streetNum":"11","zip":"53216","landPhone":"231562145","mobilePhone":"231562145","email":"test#GMAIL.IT","bankAccountKey":"123625478325621","birthDate":"18/04/1969","orderStatusId":3,"streetCode":"","parentCsrId":"2130","syncStatusId":1,"languageId":3}
If there is an error in binding, is there a way to trap this?

Answer 1

I finally got this resolved. Here is the takeaway: If you get a null model, yet data was passed in the Web Request, it means that ModelBinding failed.
In my case, a misformatted date string could not be converted to a date. The result is the entire model is null, not just the data field.
The way to get the Errors is through the ModelState object. In my case, no error message was returned. But an Exception Object WAS returned.
Here is the code to concatenate it into a string:
string desc = "";
foreach (var modelState in ViewData.ModelState.Values)
{
foreach (var error in modelState.Errors)
{
if(!String.IsNullOrWhiteSpace(error.ErrorMessage))
desc = desc + " " + error.ErrorMessage.ToString();
if(error.Exception != null)
{
desc = desc + " Exception: " + error.Exception.ToString();
}
}
}