This repo contains sample code and instructions for creating a RESTful API using .NET Core Web API to act as a proxy for various legacy data sources (REST API, SOAP API, PostgreSQL data base, SQL Server database). It is designed for people that have some coding experience and are comfortable building APIs that are interested in learning more about C# and .NET Core.

Each step in this tutorial explains how the different pieces of the Web API application are constructed, and provides an introduction to some foundational concepts for working with C#, .NET Core and Web API.

In 18F's work on legacy modernization projects, .NET and the Microsoft software stack are technologies we encounter often. These components are typically already used in the states and federal agencies we work with, which can make them a convenient choice for supporting legacy modernization efforts. But beyond the tactical advantage of using a platform that our partners are already invested in and familiar with, .NET Core and related components have a number of features that can make them a solid choice for this kind of work.

ASP.NET Web API is a framework that can be used to create RESTful web services, which are often important to our efforts to modernize legacy systems. There are a number of different patterns for migrating away from legacy systems that involve intercepting calls into the system and either rerouting them to new components, or modifying responses returned to the requester. ASP.NET Web APIs are a good fit for this use case.

Beyond this, building a Web API application is a good way to learn to write C# code, to become familiar with .NET Core, and to get accustomed to working with some associated tools like Visual Studio Code.

This tutorial is structured around git branches. Each step in the tutorial is contained within a distinct branch. If you are using the Github website, each step in the tutorial is linked from the README document in the previous step. To get the entire tutorial, and all of the related example code, just clone this repo.

• Introduction
• Part 1: Setting up a new Web API application
• Part 2: Creating Web API Controller Tests
• Part 3: Creating a REST Controller
• Part 4: Creating a SOAP Controller
• Part 5: Creating a SQL Controller (Entity Framework / SQL Server)
• Part 6: Creating a SQL Controller (Entity Framework / PostreSQL)
• Part 7: Configuration Management in Web API.

On your local machine, to see the complete code for each section in action, you should be able to git checkout part-{number} and run either dotnet test or dotnet run.

Download and install:

• .NET Core SDK
• Visual Studio Code
• VS Code C# extension

Some other useful VS Code extensions you'll need:

• VS Code Docker extension
• VS Code SQL Server extension
• Nuget Package Manager

You're ready to get started. Check out Part 1: Creating your first Web API application.

These are some resources that can supplement the steps demonstrated in this tutorial and provide deeper insights into .NET Core and Web API.

• General overview of how to create a Web API with ASP.NET Core MVC on MacOS.
• Asynchronous programming in C#.
• Video archive

• Testing controller logic in ASP.NET Core
• Unit testing C# in .NET Core using dotnet test and xUnit
• Dependency Injection in ASP.NET Core

• Data validation in ASP.NET Web API applications
• Learn about the difference between conventional routing (using routing middleware) and attribute routing in ASP.NET MVC apps.
• Learn more about how ASP.NET Web API converts a return value from a controller method into an HTTP response.

• Data access in .NET Core
• Use Visual Studio Code to create and run Transact-SQL scripts for SQL Server

• .NET Core Docker images: Official imafges for .NET Core and ASP.NET Core.
• Overview of how to run the SQL Server 2017 container image in Docker