Creating Minimal API's quickly with ASP.NET Core

In today's web development landscape, the importance of crafting lightweight and efficient APIs cannot be overstated. Minimal APIs provide an efficient way to build APIs with complexity, cutting down on unnecessary code and boosting developer efficiency. ASP.NET Core, Microsoft's open-source framework designed for web applications and services, offers a platform for developing minimal APIs. This in-depth guide will delve into utilizing ASP.NET Core to create APIs covering essential concepts, best practices, and real-world examples.

Grasping the Concept of Minimal APIs in ASP.NET Core

Introduced in ASP.NET Core 6, minimal APIs present a method of constructing APIs without the traditional reliance on controllers and routing setup. Developers can now define endpoints using straightforward C# code that taps into the language's versatility and clarity. This streamlined approach minimizes the setup complexity involved in configuring APIs, making it particularly suitable for small-scale projects, prototypes, or microservices without worrying much about the development infrastructure to host and run APIs.

Key Characteristics of Minimal APIs

1. Simplified Syntax

Minimal APIs are known for their way of defining endpoints using C# code, with lambda expressions or methods instead of traditional controllers and routing setups. This approach cuts down on code, making API implementations cleaner and more concise.

2. Built-In Dependency Injection

ASP.NET Cores minimal APIs make use of the framework's built-in dependency injection container, enabling developers to inject dependencies into endpoint handlers. This promotes separation of concerns, enhances code reusability, and allows for the injection of dependencies like database contexts, services, or repositories without manual setup. This also helps drastically when writing unit tests.

3. Integration With ASP.NET Core Middleware

Minimal APIs seamlessly work with ASP.NET Core middleware, giving developers access to features like authentication, authorization, logging of requests/responses, and handling exceptions. By incorporating middleware components into the application pipeline without compromising simplicity, developers can enhance functionality while maintaining a development experience.

4. Support for OpenAPI/Swagger

ASP.NET Core Minimal APIs offer built-in support for Swagger integration, which helps in simplifying the process of generating API documentation. When developers add the Swashbuckle. ASP.NET Core package to the project and add a few lines of code to Program.cs, Swagger endpoints get created, which can automatically create API documentation that explains request/response structures, parameters, types, and error messages. This makes it easier to document and explain the API details to end users.

Exploring the Basics of Minimal APIs in ASP.NET Core 

Now that we've delved into the concept of APIs, in ASP.NET Core, let's dive into how to kickstart the process:

Step 1. Creating a New ASP.NET Core Project From CLIB

You can open a new minimal API solution using Visual Studio or using the .NET CLI. Let's use CLI to create an empty minimal API solution by running the command below. Now open it using Visual Studio by navigating to the folder where the MinimalApiDemo solution was created. Click on the MinimalApiDemo.csproj file to open the solution

dotnet new web -n MinimalApiDemo

Step 2. Defining Minimal API Endpoints

Define minimal API endpoints within the Program.cs file using the WebApplication class. 

var builder = WebApplication.CreateBuilder(args);

var app = builder.Build();

app.MapGet("/", () => "Hello World!");
app.MapGet("/greeting", () => "Welcome to my article about Minimal API!");

app.Run();

By default, you will get the Hello World endpoint out of the box, let's add another endpoint as shown in the above code snippet. We created an API endpoint that produces a greeting message by writing a single line. Creating API services can't get any simpler than this.

Step 3. Launching the Application

Use CLI to run the application or directly press F5 from Visual Studio. 

dotnet run

Visit http://localhost:5000/greeting in your web browser to view the response from the API endpoint to see the output, or Visual Studio will automatically open the browser as shown in the below figure.

 

Step 4. Adding Swagger Endpoints

To add Swagger to your project, you need to first install the below package directly from your Visual Studio package manager console.

dotnet add package Swashbuckle.AspNetCore

Modify your Program.cs to add the swaggerGenerator method and define the Swagger UI endpoint as shown below. 

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddEndpointsApiExplorer(); // This is required for Swagger
builder.Services.AddSwaggerGen(); // This adds Swagger Generator

var app = builder.Build();

// Enable middleware to serve generated Swagger as a JSON endpoint.
app.UseSwagger();

// Enable middleware to serve swagger-ui (HTML, JS, CSS, etc.),
// specifying the Swagger JSON endpoint.
app.UseSwaggerUI(c =>
{
    c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
});

app.MapGet("/", () => "Hello World!");

app.MapGet("/greeting", () => "Welcome to my article about Minimal API!");

app.Run();

When you run the application, you can now go to the Swagger endpoint by adding /swagger to the URL, which will open below the Swagger UI with details about your endpoints. 

Best Practices for Developing Minimal APIs in ASP.NET Core

To ensure fast sailing with your API development endeavors, it's crucial to adhere to these best practices.

1. Simplify and Focus on Endpoints

Make sure to create specific and straightforward endpoints for each task. Avoid creating complex endpoints that try to do too many things. Keeping your endpoints simple and focused makes your code easier to understand and debug.

2. Harness Dependency Injection

Use ASP.NET Core’s built-in tool for dependency injection to add dependencies to endpoint handlers. It’s crucial not to tie your endpoint logic with dependencies; instead, inject them as services. This approach enhances code reusability, testability, and maintainability by allowing for a separation of concerns.

3. Manage Errors Effectively

Ensure that your code includes error-handling mechanisms to manage exceptions and unforeseen issues in a manner. Utilize HTTP status codes and clear error messages to effectively communicate any errors to users. Be cautious not to reveal data, in error responses, and offer instructions on how users can address the problem.

4. Incorporate Validation and Input Sanitization Procedures

Make sure to check and clean up the input data to avoid security risks, like SQL injection or cross-site scripting (XSS) attacks. Employ data annotations, model validation attributes, or customized validation methods to maintain data security and integrity. Discard any incorrect input. Offer helpful error messages to users when needed.

5. Embrace Versioning and Documentation Practices

Utilize version control and documentation methods to guarantee operation and simplify connections with customer programs. Employ OpenAPI/Swagger for the creation of API documentation. Offer thorough explanations of endpoints, parameters, and response structures. Maintain versions of your APIs to ensure support for iterations and offer explicit instructions on transitioning clients to updated versions.

By adhering to these recommendations, you can construct APIs in ASP.NET Core that are effective, adaptable, and easy to manage. Ensure that your endpoints are straightforward and make use of dependency injection, manage errors with care, incorporate validation, input cleaning procedures, and offer documentation. By adopting these recommended approaches, you can develop APIs that cater to user requirements and facilitate integration with client applications.

Practical Instances of Minimal APIs in ASP.NET Core

Let's delve into some real scenarios demonstrating the power of creating minimal APIs in ASP.NET Core. Imagine you have an e-commerce application with product information inside a database. You want to spin up APIs to perform basic functionalities like create/read/update/delete products from the DB.

Let's write Minimal APIs for performing CRUD operations on the product class. I am using an in-memory database for simplicity.

Create a Product class and ProductContext a class inherited from DbContext (using Entity Framework to retrieve data from the DB).

public class ProductContext : DbContext
{
    public ProductContext(DbContextOptions<ProductContext> options)
        : base(options)
    {
    }

    public DbSet<Product> Products { get; set; }
}

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
}

Create/Read/Update/Delete API Endpoints inside a single file (program.cs) as shown below.

using Microsoft.EntityFrameworkCore;
using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.EntityFrameworkCore.InMemory;


var builder = WebApplication.CreateBuilder(args);
builder.Services.AddDbContext<ProductContext>(options => options.UseInMemoryDatabase("Products"));

// Add services to the container.
builder.Services.AddEndpointsApiExplorer(); // This is required for Swagger
builder.Services.AddSwaggerGen(); // This adds Swagger Generator

var app = builder.Build();
// Enable middleware to serve generated Swagger as a JSON endpoint.
app.UseSwagger();

// Enable middleware to serve swagger-ui (HTML, JS, CSS, etc.),
// specifying the Swagger JSON endpoint.
app.UseSwaggerUI(c =>
{
    c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
});


app.MapGet("/products", async (ProductContext db) =>
{
    return await db.Products.ToListAsync();
});

app.MapGet("/products/{id}", async (ProductContext db, int id) =>
{
    return await db.Products.FindAsync(id) is Product product ? Results.Ok(product) : Results.NotFound();
});

app.MapPost("/products", async (ProductContext db, Product product) =>
{
    db.Products.Add(product);
    await db.SaveChangesAsync();

    return Results.Created($"/products/{product.Id}", product);
});

app.MapPut("/products/{id}", async (ProductContext db, int id, Product inputProduct) =>
{
    if (await db.Products.FindAsync(id) is not Product product)
    {
        return Results.NotFound();
    }

    product.Name = inputProduct.Name;
    product.Price = inputProduct.Price;

    await db.SaveChangesAsync();

    return Results.NoContent();
});

app.MapDelete("/products/{id}", async (ProductContext db, int id) =>
{
    if (await db.Products.FindAsync(id) is not Product product)
    {
        return Results.NotFound();
    }

    db.Products.Remove(product);
    await db.SaveChangesAsync();

    return Results.NoContent();
});

app.Run();

We can spin up an API so fast by leveraging the power of Minimal APIs. Press F5 to open the browser. Navigate to Swagger UI by adding /swagger to the URL. Swagger UI will display all the endpoints as written in the above code block. 

How to Quickly Test It

Click on any of the collapsible endpoints to see documentation. Click on a button to try it out and execute. I clicked on the HTTP post request to add a new Product called "Rocket Ship" to the in-memory database, which can then be retrieved by calling the GET Endpoint.

Conclusion

Rapidly developing APIs using the ASP.NET Core framework presents an approach towards constructing web APIs that are lightweight yet effective. By using the syntax, built-in dependency injection, and seamless integration, with middleware provided by ASP.NET Core developers can easily craft APIs without complexity or extra steps. Adhering to recommended strategies like maintaining targeted endpoints, utilizing dependency injection effectively, and managing errors with finesse are key to ensuring the success of your API development journey.