September 19, 2018 Asp.Net MVC Troubleshooting .Net
Troubleshooting MVC Serialization
I was trying to POST from JavaScript to my Asp.Net MVC “Classic” controller and the parameter was null. I tried several different casings using $.ajax (really I’d rather use
EcmaScript Proimses
, but this project already has jQuery so I can’t rock the boat too much), but it kept serializing to null.
There was no error indication output in MVC. It turns out I was missing a comma in my POST body when using Postman/jQuery.
Here’s what I finally came up with to see the actual exception.
Let’s say you have an MVC action.
[HttpPost]
[Route("GetScore")]
public async Task<ScoreResponse> GetScore(ScoreRequest requestContent, CancellationToken cancellationToken)
{
add this to the body of your action method.
// Re-wind to read the content out of the post as MVC has already read the string
var readStream = await Request.Content.ReadAsStreamAsync();
readStream.Seek(0, System.IO.SeekOrigin.Begin);
var content = await this.Request.Content.ReadAsStringAsync();
var r = JsonConvert.DeserializeObject<ScoreDto>(content);
Note: If the content is null or you get an “This stream does not support seek operations.” then your JSON object in the body must have some bad properties or missing a comma. Reduce the JSON down to the simplest form possible until you get something that is non-null.
Now in the response, you’ll get the exception (or you could try catch the DeserializeObject)
{
"Message": "An error has occurred.",
"ExceptionMessage": "After parsing a value an unexpected character was encountered: \". Path 'FirstName', line 5, position 0.",
"ExceptionType": "Newtonsoft.Json.JsonReaderException",
"StackTrace": " at Newtonsoft.Json.JsonTextReader.ParsePostValue(Boolean ignoreComments)\r\n at Newtonsoft.Json.JsonTextReader.Read()\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)\r\n at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)\r\n at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)\r\n at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSetting
}
Other things to look for
- you have “NULL” instead of “null” in your JSON. Note the casing!
public string P {get; set; }was set to null in the body of your JSON.
I hope this helps someone.
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