ASP.NET Core – How to receive a file in a web API request

When the client posts a file in a multipart/form-data request, it’s loaded into an IFormFile object. This contains file information (such as the file name) and exposes the file content as a stream. This allows you to save the file or process it however you want to. You can access the IFormFile object through Request.Form.Files: … Read more

ASP.NET Core – How to return a 500 response

The simplest way to return a 500 response is to use the Problem() helper method, like this: This produces the following response: The ControllerBase class has many helper methods like Problem() that simplify returning responses. These have several optional parameters that you can use to customize the response. Internally, these helper methods return result objects. … Read more

ASP.NET Core – Getting query string values

The ASP.NET Core framework automatically parses query strings (i.e. ?name=Dune&year=2021) into HttpContext.Request.Query and maps the query string values to action parameters (if you’ve added them). You can get the mapped query string values by adding action parameters, like this: Or you can use HttpContext.Request.Query directly (which is useful in many scenarios): This can either return … Read more

C# – Sending query strings with HttpClient

Query strings start with ‘?’ and have one or more key-value pairs separated by ‘&’. All characters except a-z, A-Z, 0-9 have to be encoded, including Unicode characters. When you use HttpClient, it automatically encodes the URI for you (internally, it delegates this task to the Uri class). This means when you include a query … Read more

ASP.NET Core – How to unit test an action filter

To unit test an action filter, you have to pass in an action filter context object (which requires a lot of setup). Action filter methods are void, so you have to verify the behavior by inspecting the context object (or dependencies, like a logger, if you are injecting those). Here’s an example of doing the … Read more

ASP.NET Core – How to add your own action filter

Action filters allow you to look at requests right before they are routed to an action method (and responses right after they are returned from the action method). The simplest way to add your own action filter in ASP.NET Core is to subclass ActionFilterAttribute and then override the appropriate methods depending on if you want … Read more

ASP.NET Core – Get posted form data in an API Controller

To get posted form data in an API Controller (using the [ApiController] attribute) in ASP.NET Core, use parameters with the [FromForm] attribute. A request to this endpoint would look like this: The form data is a string of key-value pairs (ex: location=United+States). The framework tries to map the form data to parameters by matching the … Read more

C# – Circuit breaker with Polly

In an electrical system, a circuit breaker detects electrical problems and opens the circuit, which blocks electricity from flowing. To get electricity flowing again, you have to close the circuit. The same approach can be implemented in software when you’re sending requests to an external service. This is especially important when you’re sending lots of … Read more

C# – Global exception event handlers

There are two global exception event available in all .NET applications: FirstChanceException: When any exception is thrown, this event is fired before anything else. UnhandledException: When there’s an unhandled exception, this event is fired right before the process is terminated. You wire up these event handlers in Main() (before anything else has executed), like this: … Read more

ASP.NET Core – Log messages to the database in the background

I was reading about logging in ASP.NET when I came across this statement about logging to the database: When logging to SQL Server, don’t do so directly. Instead, add log messages to an in-memory queue and have a background worker dequeue and insert data to SQL Server. Paraphrased from https://docs.microsoft.com/en-us/aspnet/core/fundamentals/logging/?view=aspnetcore-5.0#no-asynchronous-logger-methods In this article, I’ll show … Read more