apicontroller

ASP.NET Core – How to manually validate a model in a controller

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Manually validating a model can mean a few different things. It depends on what you’re trying to do exactly. Are you trying to validate a model object against its validation attributes? Use TryValidateModel(). Are you trying to do validation logic manually (instead of using validation attributes)? You can add errors to ModelState in that case. … Read more

ASP.NET Core – Only one parameter per action may be bound from body

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When you have multiple parameters on an action method that are bound to the request body (implicitly or explicitly), you get the following fatal exception upon starting the web API: System.InvalidOperationException: Action ‘RecipeController.Post’ has more than one parameter that was specified or inferred as bound from request body. Only one parameter per action may be … Read more

ASP.NET Core – Four basic ways to receive parameters

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There are four basic ways to receive parameters in an ASP.NET Core Web API: query strings, path parameters, request body, and request headers. I’ll show examples of these below. Query string parameters Let’s say you have two query string keys: name and servings. To get these query string values, add method parameters with names that … Read more

C# – How to disable ModelStateInvalidFilter

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There are two options for disabling ModelStateInvalidFilter: You’d do this when you want to manually perform model validation. I’ll show both options below. Disable ModelStateInvalidFilter globally To disable ModelStateInvalidFilter for *all* actions, set SuppressModelStateInvalidFilter=true in ConfigureApiBehaviorOptions, like this: Disable ModelStateInvalidFilter for specific actions To disable ModelStateInvalidFilter selectively, you can implement an IActionModelConvention attribute that removes … Read more

ASP.NET Core – API model validation attributes

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It’s always a good idea to validate data coming into your web API. There are two steps you can do to guard against invalid data: Here’s an example of using model validation attributes: When a request comes in, the framework does two things: Let’s say you send a request with invalid data (boxOfficeMillions is outside … Read more

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

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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 content or process it however you want to. You can access the IFormFile object through … Read more

ASP.NET Core – How to return a 500 response

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The simplest way to return a 500 response is to use the Problem() helper method, like this: This method returns an ObjectResult with status code 500 and a generic error message, which gets serialized to JSON and returned in the response body. The response looks like this: The ControllerBase class has many helper methods like … Read more

Add a custom action filter in ASP.NET Core

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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

C# – Get all classes with a custom attribute

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To get all classes with a custom attribute, first get all types in the assembly, then use IsDefined(customAttributeType) to filter the types: This is looking for classes in the current assembly that have the [ApiController] attribute, such as this controller class: This is useful in several scenarios, such as when you want to log information … Read more

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

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

C# – Dependency inject BackgroundService into controllers

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Let’s say you have a hosted BackgroundService called DatabaseLoggerService. It runs in the background and logs messages to the database. It has the following definition: You want your controllers to use this for logging. In other words, you want them to depend on ILoggerService, not the concrete DatabaseLoggerService class. First, constructor inject ILoggerService into your … Read more

How to use NLog in ASP.NET

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When you want to use NLog in ASP.NET, the first step is to install and configure NLog. Then you can either use it directly or fully integrate it 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 – How to unit test an ApiController

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The key to unit testing an ApiController class is to mock out all of its dependencies, including the controller’s HttpContext property, like this: If the controller method you’re testing uses anything from the HttpContext, then you’ll want to swap in your own value. Otherwise HttpContext will be null and you’ll get a NullReferenceException. Fortunately Microsoft … Read more

C# – How to read configuration from appsettings.json

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The appsettings.json file is a convenient way to store and retrieve your application’s configuration. You can add it to any project and then use the Microsoft.Extensions.Configuration library to work with it. Since appsettings.json is just a JSON file, you can add any section / values you want (this is easier than working with XML-based app.config … Read more

ASP.NET – Async SSE endpoint

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Server-Sent Events (SSE) allow a client to subscribe to messages on a server. The server pushes new messages to the client as they happen. This is an alternative to the client polling the server for new messages. In this article I’ll show how to implement the messaging system shown in the diagram below. This uses … Read more