How to Create API in .NET Core

Goal to Achieve

We have a fictional company that needs to expose a set of methods to perform these operations:

• Create a product
• Read a product
• Update a product
• Delete a product

The external applications which are going to consume these API methods have a screen like this:

In this case, we have an entity called Product with 4 fields:

• Product (int)
• Name (string)
• ImageUrl (string)
• Price (decimal)

Before we start coding, I encourage you to refresh the basic concepts about API and JSON format.

What are APIs?

I have read a lot of definitions about this concept and I have preferred to keep this in my mind:

APIs is the specification of how one piece of software can interact with another.

In our example, we are going to create a set of pieces (“methods”) that will be in charge of doing a specific task interacting with external applications.

Operation	Http Verb
Create a product	POST
Read a product	GET
Update a product	UPDATE
Delete a product	DELETE

What is JSON?

• JSON stands for JavaScript Object Notation
• JSON is a lightweight format for storing and transporting data
• JSON is often used when data is sent from a server to a web page
• JSON is “self-describing” and easy to understand

So, let´s start coding.

Step 1: Run Dotnet Command

Open the command line window and go to your repositories folder and create a new API project by typing the next dotnet command:

dotnet new webapi - n crudstore

Step 2: Explore Your Project

Go inside your project crudstore, by typing:

cd crudstore

Open your project in vscode, by typing:

code .

Step 3: Set Up Your Environment

Click on the extension panel and explore a great amount of tools that will help you to prepare your environment and be more productive.

Personally, I would recommend you to install:

• C#
• C# Extension

Step 4: Creating the Model

namespace Models
{
public class Product

{
public int Idproduct { get; set; }
public string Name { get; set; }
public string Imageurl { get; set; }
public decimal Price { get; set; }
}
}

Step 5: Creating the Controller

I will use static collections of products to illustrate this example, but in a real scenario, certainly, you will have to add more code to connect with the database.

static List<product> _products = new List<product>(){
            new Product(){ Idproduct =0, Name= "hard disk", Price= 100  },
            new Product(){ Idproduct =1, Name= "monitor", Price= 250  },
        };

After that, add the next code to handle all the requests.

Be aware that you have to use some namespaces in the header:

using System.Collections.Generic;
using System.Linq;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Models;</code>

[Produces("application/json")]
    [ApiController]
    [Route("api/products")]
    public class productController : Controller
    {
        static List<Product> _products = new List<Product>(){
            new Product(){ Idproduct =0, Name= "hard disk", Price= 100  },
            new Product(){ Idproduct =1, Name= "monitor", Price= 250  },
        };

        [HttpGet("GetAll")]
        public IActionResult GetAll()
        {
            return Ok(_products);
        }

        [HttpPost]
        public IActionResult Post([FromBody] Product product)
        {
            _products.Add(product);
            return StatusCode(StatusCodes.Status201Created);
        }

        [HttpPut]
        public IActionResult Put([FromBody] Product product)
        {
            var entity = _products.Where
                         (x => x.Idproduct == product.Idproduct).FirstOrDefault();
            entity.Name =  product.Name;
            entity.Price = product.Price;
            entity.Imageurl =  product.Imageurl;
            return StatusCode(StatusCodes.Status200OK);
        }

        [HttpDelete]
        public IActionResult Delete([FromBody] Product product)
        {
            var entity = _products.Where
                         (x => x.Idproduct == product.Idproduct).FirstOrDefault();
            _products.Remove(entity);
            return StatusCode(StatusCodes.Status200OK);
        }
    }

Step 6: Add Swagger to Your Project

Swagger is a nugget very useful to document and describe all the methods in your API.
In the command line and inside of your project, type the next command:

dotnet add package Swashbuckle.AspNetCore

As a result, you will see a message like this:

Go to the startup.cs class in your project and make some changes to allow that swagger can be configured appropriately.

In the method Configureservices, add this code:

services.AddCors(o => o.AddPolicy("MyPolicy", builder =>
            {
                builder.AllowAnyOrigin()
                    .AllowAnyMethod()
                    .AllowAnyHeader();
            }));
            // Register the Swagger generator, defining 1 or more Swagger documents
            services.AddSwaggerGen();

After that, go to the Configure method in the Startup class and add this code:

// 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");
            });

Finally, your Startup class should be like this:

public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. 
        // Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();
            services.AddCors(o => o.AddPolicy("MyPolicy", builder =>
            {
                builder.AllowAnyOrigin()
                    .AllowAnyMethod()
                    .AllowAnyHeader();
            }));
            // Register the Swagger generator, defining 1 or more Swagger documents
            services.AddSwaggerGen();
        }

        // This method gets called by the runtime. 
        // Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            // 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.UseHttpsRedirection();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }

Step 7: Testing your API

Type the next command in the command line window:

dotnet run

Step 8: Verifying the Results

Open the browser and type the url https://localhost:5001/swagger/index.html, you will see the set of methods that we created previously.

Method GetAll

Url: https://localhost:5001/api/products/GetAll

[
{
"idproduct": 0,
"name": "hard disk",
"imageurl": null,
"price": 100
},
{
"idproduct": 1,
"name": "monitor",
"imageurl": null,
"price": 250
}
]

Method Post

Url: https://localhost:5001/api/products

{
  "idproduct": 0,
  "name": "watch",
  "imageurl": "http://url",
  "price": 150
}

You can explore all the features that Swagger offers to test the APIs, therefore you have other interesting alternatives like Postman and Fiddler to test the APIs.

I hope you enjoy this code!

• Download this code for Github