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How can I throw an exception in an ASP.NET Core WebAPI controller that returns an object?

In Framework WebAPI 2, I have a controller that looks like this:

[Route("create-license/{licenseKey}")]
public async Task<LicenseDetails> CreateLicenseAsync(string licenseKey, CreateLicenseRequest license)
{
    try
    {
        // ... controller-y stuff
        return await _service.DoSomethingAsync(license).ConfigureAwait(false);
    }
    catch (Exception e)
    {
        _logger.Error(e);
        const string msg = "Unable to PUT license creation request";
        throw new HttpResponseException(HttpStatusCode.InternalServerError, msg);
    }
}

Sure enough, I get back a 500 error with the message.

How can I do something similar in ASP.NET Core Web API?

HttpRequestException doesn't seem to exist. I would prefer to continue returning the object instead of HttpRequestMessage.

8 months ago · Santiago Trujillo

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It's better not to catch all exceptions in every action. Just catch exceptions you need to react specifically and catch (and wrap to HttpResponse) all the rest in Middleware.

8 months ago · Santiago Trujillo Report

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Accepted Answer · 2022-06-13T20:04:06.715Z

What about something like this. Create a middleware where you will expose certain exception messages:

public class ExceptionMiddleware
{
    private readonly RequestDelegate _next;

    public ExceptionMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        try
        {
            await _next(context);
        }
        catch (Exception ex)
        {
            context.Response.ContentType = "text/plain";
            context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;

            if (ex is ApplicationException)
            {
                await context.Response.WriteAsync(ex.Message);
            }
        }
    }
}

Use it in your app:

app.UseMiddleware<ExceptionMiddleware>();
app.UseMvc();

And then in your action throw the exception:

[Route("create-license/{licenseKey}")]
public async Task<LicenseDetails> CreateLicenseAsync(string licenseKey, CreateLicenseRequest license)
{
    try
    {
        // ... controller-y stuff
        return await _service.DoSomethingAsync(license).ConfigureAwait(false);
    }
    catch (Exception e)
    {
        _logger.Error(e);
        const string msg = "Unable to PUT license creation request";
        throw new ApplicationException(msg);
    }
}

A better approach is to return an IActionResult. That way you dont have to throw an exception around. Like this:

[Route("create-license/{licenseKey}")]
public async Task<IActionResult> CreateLicenseAsync(string licenseKey, CreateLicenseRequest license)
{
    try
    {
        // ... controller-y stuff
        return Ok(await _service.DoSomethingAsync(license).ConfigureAwait(false));
    }
    catch (Exception e)
    {
        _logger.Error(e);
        const string msg = "Unable to PUT license creation request";
        return StatusCode((int)HttpStatusCode.InternalServerError, msg)
    }
}