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 – 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# – How to use Polly to do retries

Whenever you’re dealing with code that can run into transient errors, it’s a good idea to implement retries. Transient errors, by definition, are temporary and subsequent attempts should succeed. When you retry with a delay, it means you think the the transient error will go away by itself after a short period of time. When … 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 In this article, I’ll show … Read more

ASP.NET Core – Dependency inject a background service into the controllers

Let’s say you have a background service called DatabaseLoggerService. It runs as a hosted background service and logs messages to the database. It has the following definition: You want your controllers to use this for logging. They don’t need to know about the concrete DatabaseLoggerService class, and they don’t need to know they are actually … Read more

How to use NLog in ASP.NET

When you want to use NLog in ASP.NET, the first step is to install and configure NLog. Then you can either use NLog directly or fully integrate NLog and ASP.NET. Use NLog directly if you prefer to have static ILogger properties, instead of using dependency injection. The downside of this approach is that you’ll have … Read more

ASP.NET Core – Self-hosted service stub with a command line interface

When you’re integrating with a third-party API, you may want to send requests to a service stub instead of sending them to the real API. The purpose of a service stub is to simulate the third-party API by returning hardcoded responses. This is similar to how mocks are used in unit testing – it helps … Read more