Why isn't FromQuery working in my ASP.Net Core 1.1 controller action

Question

I am working on an ASP.Net Core 1.1 web API. I have a ServiceTypeCode controller as shown below;

[Produces("application/json")]
[Route("api/[controller]")]
public class ServiceTypeCodeController : Controller
{ 
    ...
    ...
    ...


    [HttpGet]
    public IActionResult Get([FromQuery] string a_query)
    {
        try
        {
            if (string.IsNullOrEmpty(a_query))
            {
                OperationResult<List<ServiceTypeCode>, string> result = m_bl.GetAllServiceTypeCodes();
                if (result.Success && result.Result.Count > 0)
                {
                    return Ok(JsonConvert.SerializeObject(result.Result));
                }
            } else
            {
                // Deserialize query into dictionary of strings and StringValues 
                var query = QueryHelpers.ParseQuery(a_query.ToLower());

                if (query.TryGetValue("mailclasscode", out var mailClassCode))
                {
                    if (!string.IsNullOrEmpty(mailClassCode))
                    {
                        OperationResult<List<ServiceTypeCode>, string> result = m_bl.GetAllServiceTypeCodes(mailClassCode);
                        if (result.Success && result.Result.Count > 0)
                        {
                            return Ok(JsonConvert.SerializeObject(result.Result));
                        }
                    }
                }
                if (query.TryGetValue("stc", out var stc))
                {
                    if (!string.IsNullOrEmpty(stc))
                    {
                        OperationResult<ServiceTypeCode, string> result = m_bl.GetServiceTypeCode(stc);
                        if (result.Success)
                        {
                            return Ok(JsonConvert.SerializeObject(result.Result));
                        }
                    }
                }
            }
            return NotFound();
        }
        catch (Exception ex)
        {
            string msg = "An exception occurred while trying to get a list of ServiceTypeCodes from the database.";
            m_logger.LogError(1, ex, msg);
            ApiError error = BuildError("Server Error - Exception", "500", "Get", ex, msg);
            return Ok(JsonConvert.SerializeObject(error));
        }

    }

If I use the url ...

http://localhost:5000/api/servicetypecodes

in PostMan with the GET verb, I get the list of service type codes, as expected. However, If I try to add anything as a query string, such as ...

http://localhost:5000/api/servicetypecodes?mailclasscode=fc

and set a breakpoint in my code at the

if (string.IsNullOrEmpty(a_query))

location, the value of a_query is null instead of the expected "mailclasscode=fc"

What am I missing here?

Thanks in advance for any help.

Answer 1

The .Net Core Controller Method's variable names must be the same as what you are sending.

http://localhost:5000/api/servicetypecodes?mailclasscode=fc

If using that url to pass data the controller method will have to look like this:

[HttpGet]
public IActionResult Get([FromQuery] string mailclasscode)
{...}

Or vice versa.

Good luck - happy coding.

Answer 2

You can have the query string name differ from the variable name in the method. You have to let .NetCore know how by defining it in code like so (using your variable names):

[HttpGet]
public IActionResult Get([FromQuery(Name = "mailclasscode")] string a_query)
{
   ...
}

or more generically:

[HttpGet]
public IActionResult Get([FromQuery(Name = "myQueryStringParamName")] string myCodeParamName)
{
   ...
}