As ASP.NET developers, Web API offers a powerful way to build HTTP services that can be consumed by a wide range of clients, from JavaScript in the browser to native iOS and Android apps. If you've already taken the first steps into ASP.NET Web API, you're likely eager to explore its more advanced features. This tutorial will guide you through some of these, helping you take your Web API skills to the next level.
In this tutorial, we'll cover a range of advanced topics, from API versioning and filtering, to working with file uploads and downloads, and even delving into real-time communications with WebSockets. We'll also explore unit testing and what's new in ASP.NET Core 3.0. By the end, you'll be well-equipped to handle even the most challenging Web API tasks.
API Versioning
API versioning is crucial for maintaining compatibility with older clients while introducing new features. ASP.NET Web API provides built-in support for versioning through the API controller selection process.
To start, we'll create different versions of our API by simply adding a number to the controller name, like `v1` or `v2`. We'll also learn how to route requests to the correct version based on the version in the request headers, or use a query string parameter convention.
Versioning by URI
Versioning by URI is the simplest approach, where the version number is included in the API route. We'll create versions of our API like `/api/v1/products` and `/api/v2/products`.
To route requests to the correct version, we'll use route constraints and routes with defaults. For example, `{version:apiVersion=1}` will match any URI segment that contains '1', like `/1/products`.
Versioning by headers or query strings
Another approach is to include the version number in the request headers or as a query string parameter. This keeps the URI structure clean and allows clients to request a specific version even if the default has changed.
To implement this, we'll use the `[ApiVersion]` attribute and special route parameters. For headers, we'll use `api versione: v=2`, and for query strings, `?api-versione=2`. We'll also learn how to set the default version globally or on a controller basis.
Input and Output filtering
![Fully basic CRUD Operation using ASP.NET Core Web API Example [For Beginners]](https://i.pinimg.com/originals/99/cd/5d/99cd5da84255d2d39f4856e5d9bab279.jpg)
Sometimes, we don't want to expose all the data in our models to the client, or we need to transform the data before sending it. Web API provides several ways to control the input and output data.
Model binding and validation
Model binding allows us to fill our complex models with data from the HTTP request. We'll use data annotations for validation and customize the model state for better error handling.
To filter input data, we'll use data annotations like `[Required]`, `[StringLength]`, and custom validation attributes. We'll also explore client-side validation and remote validation using `IValidationAttribute`.
JSON serializing and deserializing
Web API includes integration with `DataContractJsonSerializer` by default, but we can use the `JsonNetFormat` attribute for improved serialization performance and options. We'll also learn how to handle cycles, virtual paths, and object graphs.
For output filtering, we'll use `Json.net` or `Newtonsoft.Json` to control the serialization output. We'll use attributes like `[JsonProperty]`, `[JsonIgnore]`, and `[JsonConverter]` to filter properties and control the serialization process.
As we conclude this advanced look into ASP.NET Web API, we've scratched the surface of many powerful features that can help you build robust and maintainable APIs. The next step is to explore the new enhancements in ASP.NET Core 3.0, delve into real-time communications with WebSockets, and ensure your APIs are secure and reliable with unit testing and integration testing techniques.