Tutorial: Create a controller-based web API with ASP.NET Core

This tutorial teaches the basics of building a controller-based web API that uses a database. Another approach to creating APIs in ASP.NET Core is to create minimal APIs. For help with choosing between minimal APIs and controller-based APIs, see APIs overview. For a tutorial on creating a minimal API, see Tutorial: Create a minimal API with ASP.NET Core.

This tutorial creates the following API:

The following diagram shows the design of the app.

The project template creates a WeatherForecast API with support for OpenAPI.

...
info: Microsoft.Hosting.Lifetime[14]
   Now listening on: https://localhost:7260
info: Microsoft.Hosting.Lifetime[14]
   Now listening on: http://localhost:7261
info: Microsoft.Hosting.Lifetime[0]
   Application started. Press Ctrl+C to shut down.
...

[
    {
        "date": "2025-07-16",
        "temperatureC": 52,
        "temperatureF": 125,
        "summary": "Mild"
    },
    {
        "date": "2025-07-17",
        "temperatureC": 36,
        "temperatureF": 96,
        "summary": "Warm"
    },
    {
        "date": "2025-07-18",
        "temperatureC": 39,
        "temperatureF": 102,
        "summary": "Cool"
    },
    {
        "date": "2025-07-19",
        "temperatureC": 10,
        "temperatureF": 49,
        "summary": "Bracing"
    },
    {
        "date": "2025-07-20",
        "temperatureC": -1,
        "temperatureF": 31,
        "summary": "Chilly"
    }
]

...
info: Microsoft.Hosting.Lifetime[14]
      Now listening on: https://localhost:{port}
...

[
    {
        "date": "2025-07-16",
        "temperatureC": 52,
        "temperatureF": 125,
        "summary": "Mild"
    },
    {
        "date": "2025-07-17",
        "temperatureC": 36,
        "temperatureF": 96,
        "summary": "Warm"
    },
    {
        "date": "2025-07-18",
        "temperatureC": 39,
        "temperatureF": 102,
        "summary": "Cool"
    },
    {
        "date": "2025-07-19",
        "temperatureC": 10,
        "temperatureF": 49,
        "summary": "Bracing"
    },
    {
        "date": "2025-07-20",
        "temperatureC": -1,
        "temperatureF": 31,
        "summary": "Chilly"
    }
]

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
    app.UseSwaggerUi(options =>
    {
        options.DocumentPath = "/openapi/v1.json";
    });
}

A model is a set of classes that represent the data that the app manages. The model for this app is the TodoItem class.

namespace TodoApi.Models;

public class TodoItem
{
    public long Id { get; set; }
    public string? Name { get; set; }
    public bool IsComplete { get; set; }
}

namespace TodoApi.Models;

public class TodoItem
{
    public long Id { get; set; }
    public string? Name { get; set; }
    public bool IsComplete { get; set; }
}

The Id property functions as the unique key in a relational database.

Model classes can go anywhere in the project, but the Models folder is used by convention.

The database context is the main class that coordinates Entity Framework functionality for a data model. This class is created by deriving from the Microsoft.EntityFrameworkCore.DbContext class.

In ASP.NET Core, services such as the DB context must be registered with the dependency injection (DI) container. The container provides the service to controllers.

Update Program.cs with the following highlighted code:

using Microsoft.EntityFrameworkCore;
using TodoApi.Models;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddOpenApi();
builder.Services.AddDbContext<TodoContext>(opt =>
    opt.UseInMemoryDatabase("TodoList"));

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

The preceding code:

• Adds using directives.
• Adds the database context to the DI container.
• Specifies that the database context will use an in-memory database.

dotnet add package Microsoft.VisualStudio.Web.CodeGeneration.Design
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
dotnet add package Microsoft.EntityFrameworkCore.Tools
dotnet tool uninstall -g dotnet-aspnet-codegenerator
dotnet tool install -g dotnet-aspnet-codegenerator
dotnet tool update -g dotnet-aspnet-codegenerator

echo 'export PATH=$HOME/.dotnet/tools:$PATH' >> ~/.bashrc
source ~/.bashrc

dotnet aspnet-codegenerator controller -name TodoItemsController -async -api -m TodoItem -dc TodoContext -outDir Controllers

The generated code:

• Marks the class with the [ApiController] attribute. This attribute indicates that the controller responds to web API requests. For information about specific behaviors that the attribute enables, see Create web APIs with ASP.NET Core.
• Uses DI to inject the database context (TodoContext) into the controller. The database context is used in each of the CRUD methods in the controller.

The ASP.NET Core templates for:

• Controllers with views include [action] in the route template.
• API controllers don't include [action] in the route template.

When the [action] token isn't in the route template, the action name (method name) isn't included in the endpoint. That is, the action's associated method name isn't used in the matching route.

Update the return statement in the PostTodoItem to use the nameof operator:

[HttpPost]
public async Task<ActionResult<TodoItem>> PostTodoItem(TodoItem todoItem)
{
    _context.TodoItems.Add(todoItem);
    await _context.SaveChangesAsync();

    //    return CreatedAtAction("GetTodoItem", new { id = todoItem.Id }, todoItem);
    return CreatedAtAction(nameof(GetTodoItem), new { id = todoItem.Id }, todoItem);
}

The preceding code is an HTTP POST method, as indicated by the [HttpPost] attribute. The method gets the value of the TodoItem from the body of the HTTP request.

For more information, see Attribute routing with Http[Verb] attributes.

The CreatedAtAction method:

• Returns an HTTP 201 status code if successful. HTTP 201 is the standard response for an HTTP POST method that creates a new resource on the server.
• Adds a Location header to the response. The Location header specifies the URI of the newly created to-do item. For more information, see 10.2.2 201 Created.
• References the GetTodoItem action to create the Location header's URI. The C# nameof keyword is used to avoid hard-coding the action name in the CreatedAtAction call.

[
  {
    "id": 1,
    "name": "walk dog",
    "isComplete": true
  }
]

Two GET endpoints are implemented:

• GET /api/todoitems
• GET /api/todoitems/{id}

The previous section showed an example of the /api/todoitems/{id} route.

Follow the POST instructions to add another todo item, and then test the /api/todoitems route using Swagger.

This app uses an in-memory database. If the app is stopped and started, the preceding GET request doesn't return any data. If no data is returned, POST data to the app.

The [HttpGet] attribute denotes a method that responds to an HTTP GET request. The URL path for each method is constructed as follows:

• Start with the template string in the controller's Route attribute:

  [Route("api/[controller]")]
  [ApiController]
  public class TodoItemsController : ControllerBase
  

• Replace [controller] with the name of the controller, which by convention is the controller class name minus the "Controller" suffix. For this sample, the controller class name is TodoItemsController, so the controller name is "TodoItems". ASP.NET Core routing is case insensitive.

• If the [HttpGet] attribute has a route template (for example, [HttpGet("products")]), append that to the path. This sample doesn't use a template. For more information, see Attribute routing with Http[Verb] attributes.

In the following GetTodoItem method, "{id}" is a placeholder variable for the unique identifier of the to-do item. When GetTodoItem is invoked, the value of "{id}" in the URL is provided to the method in its id parameter.

[HttpGet("{id}")]
public async Task<ActionResult<TodoItem>> GetTodoItem(long id)
{
    var todoItem = await _context.TodoItems.FindAsync(id);

    if (todoItem == null)
    {
        return NotFound();
    }

    return todoItem;
}

The return type of the GetTodoItems and GetTodoItem methods is ActionResult<T> type. ASP.NET Core automatically serializes the object to JSON and writes the JSON into the body of the response message. The response code for this return type is 200 OK, assuming there are no unhandled exceptions. Unhandled exceptions are translated into 5xx errors.

ActionResult return types can represent a wide range of HTTP status codes. For example, GetTodoItem can return two different status values:

• If no item matches the requested ID, the method returns a 404 status NotFound error code.
• Otherwise, the method returns 200 with a JSON response body. Returning item results in an HTTP 200 response.

Examine the PutTodoItem method:

[HttpPut("{id}")]
public async Task<IActionResult> PutTodoItem(long id, TodoItem todoItem)
{
    if (id != todoItem.Id)
    {
        return BadRequest();
    }

    _context.Entry(todoItem).State = EntityState.Modified;

    try
    {
        await _context.SaveChangesAsync();
    }
    catch (DbUpdateConcurrencyException)
    {
        if (!TodoItemExists(id))
        {
            return NotFound();
        }
        else
        {
            throw;
        }
    }

    return NoContent();
}

PutTodoItem is similar to PostTodoItem, except it uses HTTP PUT. The response is 204 (No Content). According to the HTTP specification, a PUT request requires the client to send the entire updated entity, not just the changes. To support partial updates, use HTTP PATCH.

This sample uses an in-memory database that must be initialized each time the app is started. There must be an item in the database before you make a PUT call. Call GET to ensure there's an item in the database before making a PUT call.

Use the PUT method to update the TodoItem that has Id = 1 and set its name to "feed fish". Note the response is HTTP 204 No Content.

Examine the DeleteTodoItem method:

[HttpDelete("{id}")]
public async Task<IActionResult> DeleteTodoItem(long id)
{
    var todoItem = await _context.TodoItems.FindAsync(id);
    if (todoItem == null)
    {
        return NotFound();
    }

    _context.TodoItems.Remove(todoItem);
    await _context.SaveChangesAsync();

    return NoContent();
}

Use the DELETE method to delete the TodoItem that has Id = 1. Note the response is HTTP 204 No Content.

There are many other tools that can be used to test web APIs, for example:

• http-repl
• curl. Swagger uses curl and shows the curl commands it submits.
• Fiddler

Currently the sample app exposes the entire TodoItem object. Production apps typically limit the data that's input and returned using a subset of the model. There are multiple reasons behind this, and security is a major one. The subset of a model is usually referred to as a Data Transfer Object (DTO), input model, or view model. DTO is used in this tutorial.

A DTO may be used to:

• Prevent over-posting.
• Hide properties that clients are not supposed to view.
• Omit some properties in order to reduce payload size.
• Flatten object graphs that contain nested objects. Flattened object graphs can be more convenient for clients.

To demonstrate the DTO approach, update the TodoItem class to include a secret field:

namespace TodoApi.Models;

public class TodoItem
{
    public long Id { get; set; }
    public string? Name { get; set; }
    public bool IsComplete { get; set; }
    public string? Secret { get; set; }
}

The secret field needs to be hidden from this app, but an administrative app could choose to expose it.

Verify you can post and get the secret field.

Create a DTO model in a Models/TodoItemsDTO.cs file:

namespace TodoApi.Models;

public class TodoItemDTO
{
    public long Id { get; set; }
    public string? Name { get; set; }
    public bool IsComplete { get; set; }
}

Update the TodoItemsController to use TodoItemDTO:

using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using TodoApi.Models;

namespace TodoApi.Controllers;

[Route("api/[controller]")]
[ApiController]
public class TodoItemsController : ControllerBase
{
    private readonly TodoContext _context;

    public TodoItemsController(TodoContext context)
    {
        _context = context;
    }

    // GET: api/TodoItems
    [HttpGet]
    public async Task<ActionResult<IEnumerable<TodoItemDTO>>> GetTodoItems()
    {
        return await _context.TodoItems
            .Select(x => ItemToDTO(x))
            .ToListAsync();
    }

    // GET: api/TodoItems/5
    // <snippet_GetByID>
    [HttpGet("{id}")]
    public async Task<ActionResult<TodoItemDTO>> GetTodoItem(long id)
    {
        var todoItem = await _context.TodoItems.FindAsync(id);

        if (todoItem == null)
        {
            return NotFound();
        }

        return ItemToDTO(todoItem);
    }
    // </snippet_GetByID>

    // PUT: api/TodoItems/5
    // To protect from overposting attacks, see https://go.microsoft.com/fwlink/?linkid=2123754
    // <snippet_Update>
    [HttpPut("{id}")]
    public async Task<IActionResult> PutTodoItem(long id, TodoItemDTO todoDTO)
    {
        if (id != todoDTO.Id)
        {
            return BadRequest();
        }

        var todoItem = await _context.TodoItems.FindAsync(id);
        if (todoItem == null)
        {
            return NotFound();
        }

        todoItem.Name = todoDTO.Name;
        todoItem.IsComplete = todoDTO.IsComplete;

        try
        {
            await _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException) when (!TodoItemExists(id))
        {
            return NotFound();
        }

        return NoContent();
    }
    // </snippet_Update>

    // POST: api/TodoItems
    // To protect from overposting attacks, see https://go.microsoft.com/fwlink/?linkid=2123754
    // <snippet_Create>
    [HttpPost]
    public async Task<ActionResult<TodoItemDTO>> PostTodoItem(TodoItemDTO todoDTO)
    {
        var todoItem = new TodoItem
        {
            IsComplete = todoDTO.IsComplete,
            Name = todoDTO.Name
        };

        _context.TodoItems.Add(todoItem);
        await _context.SaveChangesAsync();

        return CreatedAtAction(
            nameof(GetTodoItem),
            new { id = todoItem.Id },
            ItemToDTO(todoItem));
    }
    // </snippet_Create>

    // DELETE: api/TodoItems/5
    [HttpDelete("{id}")]
    public async Task<IActionResult> DeleteTodoItem(long id)
    {
        var todoItem = await _context.TodoItems.FindAsync(id);
        if (todoItem == null)
        {
            return NotFound();
        }

        _context.TodoItems.Remove(todoItem);
        await _context.SaveChangesAsync();

        return NoContent();
    }

    private bool TodoItemExists(long id)
    {
        return _context.TodoItems.Any(e => e.Id == id);
    }

    private static TodoItemDTO ItemToDTO(TodoItem todoItem) =>
       new TodoItemDTO
       {
           Id = todoItem.Id,
           Name = todoItem.Name,
           IsComplete = todoItem.IsComplete
       };
}

Verify you can't post or get the secret field.

See Tutorial: Call an ASP.NET Core web API with JavaScript.

See Video: Beginner's Series to: Web APIs.

For guidance on creating a reliable, secure, performant, testable, and scalable ASP.NET Core app, see Enterprise web app patterns. A complete production-quality sample web app that implements the patterns is available.

ASP.NET Core Identity adds user interface (UI) login functionality to ASP.NET Core web apps. To secure web APIs and SPAs, use one of the following:

• Microsoft Entra ID
• Azure Active Directory B2C (Azure AD B2C)
• Duende Identity Server

Duende Identity Server is an OpenID Connect and OAuth 2.0 framework for ASP.NET Core. Duende Identity Server enables the following security features:

• Authentication as a Service (AaaS)
• Single sign-on/off (SSO) over multiple application types
• Access control for APIs
• Federation Gateway

For more information, see the Duende Identity Server documentation (Duende Software website).

For information on deploying to Azure, see Quickstart: Deploy an ASP.NET web app.

View or download sample code for this tutorial. See how to download.

For more information, see the following resources:

• Create web APIs with ASP.NET Core
• Tutorial: Create a minimal API with ASP.NET Core
• Use the generated OpenAPI documents
• ASP.NET Core web API documentation with Swagger / OpenAPI
• Razor Pages with Entity Framework Core in ASP.NET Core - Tutorial 1 of 8
• Routing to controller actions in ASP.NET Core
• Controller action return types in ASP.NET Core web API
• Deploy ASP.NET Core apps to Azure App Service
• Host and deploy ASP.NET Core
• Create a web API with ASP.NET Core

This tutorial teaches the basics of building a controller-based web API that uses a database. Another approach to creating APIs in ASP.NET Core is to create minimal APIs. For help with choosing between minimal APIs and controller-based APIs, see APIs overview. For a tutorial on creating a minimal API, see Tutorial: Create a minimal API with ASP.NET Core.

This tutorial creates the following API:

The following diagram shows the design of the app.

The project template creates a WeatherForecast API with support for Swagger.

...
info: Microsoft.Hosting.Lifetime[14]
      Now listening on: https://localhost:{port}
...

The Swagger page /swagger/index.html is displayed. Select GET > Try it out > Execute. The page displays:

• The Curl command to test the WeatherForecast API.
• The URL to test the WeatherForecast API.
• The response code, body, and headers.
• A drop-down list box with media types and the example value and schema.

If the Swagger page doesn't appear, see this GitHub issue.

Swagger is used to generate useful documentation and help pages for web APIs. This tutorial uses Swagger to test the app. For more information on Swagger, see ASP.NET Core web API documentation with Swagger / OpenAPI.

Copy and paste the Request URL in the browser: https://localhost:<port>/weatherforecast

JSON similar to the following example is returned:

[
    {
        "date": "2019-07-16T19:04:05.7257911-06:00",
        "temperatureC": 52,
        "temperatureF": 125,
        "summary": "Mild"
    },
    {
        "date": "2019-07-17T19:04:05.7258461-06:00",
        "temperatureC": 36,
        "temperatureF": 96,
        "summary": "Warm"
    },
    {
        "date": "2019-07-18T19:04:05.7258467-06:00",
        "temperatureC": 39,
        "temperatureF": 102,
        "summary": "Cool"
    },
    {
        "date": "2019-07-19T19:04:05.7258471-06:00",
        "temperatureC": 10,
        "temperatureF": 49,
        "summary": "Bracing"
    },
    {
        "date": "2019-07-20T19:04:05.7258474-06:00",
        "temperatureC": -1,
        "temperatureF": 31,
        "summary": "Chilly"
    }
]

A model is a set of classes that represent the data that the app manages. The model for this app is the TodoItem class.

namespace TodoApi.Models;

public class TodoItem
{
    public long Id { get; set; }
    public string? Name { get; set; }
    public bool IsComplete { get; set; }
}

The Id property functions as the unique key in a relational database.

Model classes can go anywhere in the project, but the Models folder is used by convention.

The database context is the main class that coordinates Entity Framework functionality for a data model. This class is created by deriving from the Microsoft.EntityFrameworkCore.DbContext class.

• Enter the following code:

  using Microsoft.EntityFrameworkCore;
  
  namespace TodoApi.Models;
  
  public class TodoContext : DbContext
  {
      public TodoContext(DbContextOptions<TodoContext> options)
          : base(options)
      {
      }
  
      public DbSet<TodoItem> TodoItems { get; set; } = null!;
  }
  

In ASP.NET Core, services such as the DB context must be registered with the dependency injection (DI) container. The container provides the service to controllers.

Update Program.cs with the following highlighted code:

using Microsoft.EntityFrameworkCore;
using TodoApi.Models;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddDbContext<TodoContext>(opt =>
    opt.UseInMemoryDatabase("TodoList"));
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

The preceding code:

• Adds using directives.
• Adds the database context to the DI container.
• Specifies that the database context will use an in-memory database.

dotnet add package Microsoft.VisualStudio.Web.CodeGeneration.Design
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
dotnet add package Microsoft.EntityFrameworkCore.Tools
dotnet tool uninstall -g dotnet-aspnet-codegenerator
dotnet tool install -g dotnet-aspnet-codegenerator
dotnet tool update -g dotnet-aspnet-codegenerator

echo 'export PATH=$HOME/.dotnet/tools:$PATH' >> ~/.bashrc
source ~/.bashrc

dotnet aspnet-codegenerator controller -name TodoItemsController -async -api -m TodoItem -dc TodoContext -outDir Controllers

The generated code:

• Marks the class with the [ApiController] attribute. This attribute indicates that the controller responds to web API requests. For information about specific behaviors that the attribute enables, see Create web APIs with ASP.NET Core.
• Uses DI to inject the database context (TodoContext) into the controller. The database context is used in each of the CRUD methods in the controller.

The ASP.NET Core templates for:

• Controllers with views include [action] in the route template.
• API controllers don't include [action] in the route template.

When the [action] token isn't in the route template, the action name (method name) isn't included in the endpoint. That is, the action's associated method name isn't used in the matching route.

Update the return statement in the PostTodoItem to use the nameof operator:

[HttpPost]
public async Task<ActionResult<TodoItem>> PostTodoItem(TodoItem todoItem)
{
    _context.TodoItems.Add(todoItem);
    await _context.SaveChangesAsync();

    //    return CreatedAtAction("GetTodoItem", new { id = todoItem.Id }, todoItem);
    return CreatedAtAction(nameof(GetTodoItem), new { id = todoItem.Id }, todoItem);
}

The preceding code is an HTTP POST method, as indicated by the [HttpPost] attribute. The method gets the value of the TodoItem from the body of the HTTP request.

For more information, see Attribute routing with Http[Verb] attributes.

The CreatedAtAction method:

• Returns an HTTP 201 status code if successful. HTTP 201 is the standard response for an HTTP POST method that creates a new resource on the server.
• Adds a Location header to the response. The Location header specifies the URI of the newly created to-do item. For more information, see 10.2.2 201 Created.
• References the GetTodoItem action to create the Location header's URI. The C# nameof keyword is used to avoid hard-coding the action name in the CreatedAtAction call.

• Press Ctrl+F5 to run the app.

• In the Swagger browser window, select POST /api/TodoItems, and then select Try it out.

• In the Request body input window, update the JSON. For example,

  {
    "name": "walk dog",
    "isComplete": true
  }
  

• Select Execute

  

In the preceding POST, the Swagger UI shows the location header under Response headers. For example, location: https://localhost:7260/api/TodoItems/1. The location header shows the URI to the created resource.

To test the location header:

• In the Swagger browser window, select GET /api/TodoItems/{id}, and then select Try it out.

• Enter 1 in the id input box, and then select Execute.

  

Two GET endpoints are implemented:

• GET /api/todoitems
• GET /api/todoitems/{id}

The previous section showed an example of the /api/todoitems/{id} route.

Follow the POST instructions to add another todo item, and then test the /api/todoitems route using Swagger.

This app uses an in-memory database. If the app is stopped and started, the preceding GET request doesn't return any data. If no data is returned, POST data to the app.

The [HttpGet] attribute denotes a method that responds to an HTTP GET request. The URL path for each method is constructed as follows:

• Start with the template string in the controller's Route attribute:

  [Route("api/[controller]")]
  [ApiController]
  public class TodoItemsController : ControllerBase
  

• Replace [controller] with the name of the controller, which by convention is the controller class name minus the "Controller" suffix. For this sample, the controller class name is TodoItemsController, so the controller name is "TodoItems". ASP.NET Core routing is case insensitive.

• If the [HttpGet] attribute has a route template (for example, [HttpGet("products")]), append that to the path. This sample doesn't use a template. For more information, see Attribute routing with Http[Verb] attributes.

In the following GetTodoItem method, "{id}" is a placeholder variable for the unique identifier of the to-do item. When GetTodoItem is invoked, the value of "{id}" in the URL is provided to the method in its id parameter.

[HttpGet("{id}")]
public async Task<ActionResult<TodoItem>> GetTodoItem(long id)
{
    var todoItem = await _context.TodoItems.FindAsync(id);

    if (todoItem == null)
    {
        return NotFound();
    }

    return todoItem;
}

The return type of the GetTodoItems and GetTodoItem methods is ActionResult<T> type. ASP.NET Core automatically serializes the object to JSON and writes the JSON into the body of the response message. The response code for this return type is 200 OK, assuming there are no unhandled exceptions. Unhandled exceptions are translated into 5xx errors.

ActionResult return types can represent a wide range of HTTP status codes. For example, GetTodoItem can return two different status values:

• If no item matches the requested ID, the method returns a 404 status NotFound error code.
• Otherwise, the method returns 200 with a JSON response body. Returning item results in an HTTP 200 response.

Examine the PutTodoItem method:

[HttpPut("{id}")]
public async Task<IActionResult> PutTodoItem(long id, TodoItem todoItem)
{
    if (id != todoItem.Id)
    {
        return BadRequest();
    }

    _context.Entry(todoItem).State = EntityState.Modified;

    try
    {
        await _context.SaveChangesAsync();
    }
    catch (DbUpdateConcurrencyException)
    {
        if (!TodoItemExists(id))
        {
            return NotFound();
        }
        else
        {
            throw;
        }
    }

    return NoContent();
}

PutTodoItem is similar to PostTodoItem, except it uses HTTP PUT. The response is 204 (No Content). According to the HTTP specification, a PUT request requires the client to send the entire updated entity, not just the changes. To support partial updates, use HTTP PATCH.

This sample uses an in-memory database that must be initialized each time the app is started. There must be an item in the database before you make a PUT call. Call GET to ensure there's an item in the database before making a PUT call.

Using the Swagger UI, use the PUT button to update the TodoItem that has Id = 1 and set its name to "feed fish". Note the response is HTTP 204 No Content.

Examine the DeleteTodoItem method:

[HttpDelete("{id}")]
public async Task<IActionResult> DeleteTodoItem(long id)
{
    var todoItem = await _context.TodoItems.FindAsync(id);
    if (todoItem == null)
    {
        return NotFound();
    }

    _context.TodoItems.Remove(todoItem);
    await _context.SaveChangesAsync();

    return NoContent();
}

Use the Swagger UI to delete the TodoItem that has Id = 1. Note the response is HTTP 204 No Content.

There are many other tools that can be used to test web APIs, for example:

• Visual Studio Endpoints Explorer and .http files
• http-repl
• curl. Swagger uses curl and shows the curl commands it submits.
• Fiddler

For more information, see:

• Minimal API tutorial: test with .http files and Endpoints Explorer

Currently the sample app exposes the entire TodoItem object. Production apps typically limit the data that's input and returned using a subset of the model. There are multiple reasons behind this, and security is a major one. The subset of a model is usually referred to as a Data Transfer Object (DTO), input model, or view model. DTO is used in this tutorial.

A DTO may be used to:

• Prevent over-posting.
• Hide properties that clients are not supposed to view.
• Omit some properties in order to reduce payload size.
• Flatten object graphs that contain nested objects. Flattened object graphs can be more convenient for clients.

To demonstrate the DTO approach, update the TodoItem class to include a secret field:

namespace TodoApi.Models
{
    public class TodoItem
    {
        public long Id { get; set; }
        public string? Name { get; set; }
        public bool IsComplete { get; set; }
        public string? Secret { get; set; }
    }
}

The secret field needs to be hidden from this app, but an administrative app could choose to expose it.

Verify you can post and get the secret field.

Create a DTO model:

namespace TodoApi.Models;

public class TodoItemDTO
{
    public long Id { get; set; }
    public string? Name { get; set; }
    public bool IsComplete { get; set; }
}

Update the TodoItemsController to use TodoItemDTO:

using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using TodoApi.Models;

namespace TodoApi.Controllers;

[Route("api/[controller]")]
[ApiController]
public class TodoItemsController : ControllerBase
{
    private readonly TodoContext _context;

    public TodoItemsController(TodoContext context)
    {
        _context = context;
    }

    // GET: api/TodoItems
    [HttpGet]
    public async Task<ActionResult<IEnumerable<TodoItemDTO>>> GetTodoItems()
    {
        return await _context.TodoItems
            .Select(x => ItemToDTO(x))
            .ToListAsync();
    }

    // GET: api/TodoItems/5
    // <snippet_GetByID>
    [HttpGet("{id}")]
    public async Task<ActionResult<TodoItemDTO>> GetTodoItem(long id)
    {
        var todoItem = await _context.TodoItems.FindAsync(id);

        if (todoItem == null)
        {
            return NotFound();
        }

        return ItemToDTO(todoItem);
    }
    // </snippet_GetByID>

    // PUT: api/TodoItems/5
    // To protect from overposting attacks, see https://go.microsoft.com/fwlink/?linkid=2123754
    // <snippet_Update>
    [HttpPut("{id}")]
    public async Task<IActionResult> PutTodoItem(long id, TodoItemDTO todoDTO)
    {
        if (id != todoDTO.Id)
        {
            return BadRequest();
        }

        var todoItem = await _context.TodoItems.FindAsync(id);
        if (todoItem == null)
        {
            return NotFound();
        }

        todoItem.Name = todoDTO.Name;
        todoItem.IsComplete = todoDTO.IsComplete;

        try
        {
            await _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException) when (!TodoItemExists(id))
        {
            return NotFound();
        }

        return NoContent();
    }
    // </snippet_Update>

    // POST: api/TodoItems
    // To protect from overposting attacks, see https://go.microsoft.com/fwlink/?linkid=2123754
    // <snippet_Create>
    [HttpPost]
    public async Task<ActionResult<TodoItemDTO>> PostTodoItem(TodoItemDTO todoDTO)
    {
        var todoItem = new TodoItem
        {
            IsComplete = todoDTO.IsComplete,
            Name = todoDTO.Name
        };

        _context.TodoItems.Add(todoItem);
        await _context.SaveChangesAsync();

        return CreatedAtAction(
            nameof(GetTodoItem),
            new { id = todoItem.Id },
            ItemToDTO(todoItem));
    }
    // </snippet_Create>

    // DELETE: api/TodoItems/5
    [HttpDelete("{id}")]
    public async Task<IActionResult> DeleteTodoItem(long id)
    {
        var todoItem = await _context.TodoItems.FindAsync(id);
        if (todoItem == null)
        {
            return NotFound();
        }

        _context.TodoItems.Remove(todoItem);
        await _context.SaveChangesAsync();

        return NoContent();
    }

    private bool TodoItemExists(long id)
    {
        return _context.TodoItems.Any(e => e.Id == id);
    }

    private static TodoItemDTO ItemToDTO(TodoItem todoItem) =>
       new TodoItemDTO
       {
           Id = todoItem.Id,
           Name = todoItem.Name,
           IsComplete = todoItem.IsComplete
       };
}

Verify you can't post or get the secret field.

See Tutorial: Call an ASP.NET Core web API with JavaScript.

See Video: Beginner's Series to: Web APIs.

For guidance on creating a reliable, secure, performant, testable, and scalable ASP.NET Core app, see Enterprise web app patterns. A complete production-quality sample web app that implements the patterns is available.

ASP.NET Core Identity adds user interface (UI) login functionality to ASP.NET Core web apps. To secure web APIs and SPAs, use one of the following:

• Microsoft Entra ID
• Azure Active Directory B2C (Azure AD B2C)
• Duende Identity Server

Duende Identity Server is an OpenID Connect and OAuth 2.0 framework for ASP.NET Core. Duende Identity Server enables the following security features:

• Authentication as a Service (AaaS)
• Single sign-on/off (SSO) over multiple application types
• Access control for APIs
• Federation Gateway

For more information, see the Duende Identity Server documentation (Duende Software website).

For information on deploying to Azure, see Quickstart: Deploy an ASP.NET web app.

View or download sample code for this tutorial. See how to download.

For more information, see the following resources:

• Create web APIs with ASP.NET Core
• Tutorial: Create a minimal API with ASP.NET Core
• ASP.NET Core web API documentation with Swagger / OpenAPI
• Razor Pages with Entity Framework Core in ASP.NET Core - Tutorial 1 of 8
• Routing to controller actions in ASP.NET Core
• Controller action return types in ASP.NET Core web API
• Deploy ASP.NET Core apps to Azure App Service
• Host and deploy ASP.NET Core
• Create a web API with ASP.NET Core

This tutorial teaches the basics of building a controller-based web API that uses a database. Another approach to creating APIs in ASP.NET Core is to create minimal APIs. For help with choosing between minimal APIs and controller-based APIs, see APIs overview. For a tutorial on creating a minimal API, see Tutorial: Create a minimal API with ASP.NET Core.

This tutorial creates the following API:

The following diagram shows the design of the app.

The project template creates a WeatherForecast API with support for Swagger.

...
info: Microsoft.Hosting.Lifetime[14]
      Now listening on: https://localhost:{port}
...

The Swagger page /swagger/index.html is displayed. Select GET > Try it out > Execute. The page displays:

• The Curl command to test the WeatherForecast API.
• The URL to test the WeatherForecast API.
• The response code, body, and headers.
• A drop-down list box with media types and the example value and schema.

If the Swagger page doesn't appear, see this GitHub issue.

Swagger is used to generate useful documentation and help pages for web APIs. This tutorial uses Swagger to test the app. For more information on Swagger, see ASP.NET Core web API documentation with Swagger / OpenAPI.

Copy and paste the Request URL in the browser: https://localhost:<port>/weatherforecast

JSON similar to the following example is returned:

[
    {
        "date": "2019-07-16T19:04:05.7257911-06:00",
        "temperatureC": 52,
        "temperatureF": 125,
        "summary": "Mild"
    },
    {
        "date": "2019-07-17T19:04:05.7258461-06:00",
        "temperatureC": 36,
        "temperatureF": 96,
        "summary": "Warm"
    },
    {
        "date": "2019-07-18T19:04:05.7258467-06:00",
        "temperatureC": 39,
        "temperatureF": 102,
        "summary": "Cool"
    },
    {
        "date": "2019-07-19T19:04:05.7258471-06:00",
        "temperatureC": 10,
        "temperatureF": 49,
        "summary": "Bracing"
    },
    {
        "date": "2019-07-20T19:04:05.7258474-06:00",
        "temperatureC": -1,
        "temperatureF": 31,
        "summary": "Chilly"
    }
]

A model is a set of classes that represent the data that the app manages. The model for this app is the TodoItem class.

namespace TodoApi.Models;

public class TodoItem
{
    public long Id { get; set; }
    public string? Name { get; set; }
    public bool IsComplete { get; set; }
}

The Id property functions as the unique key in a relational database.

Model classes can go anywhere in the project, but the Models folder is used by convention.

The database context is the main class that coordinates Entity Framework functionality for a data model. This class is created by deriving from the Microsoft.EntityFrameworkCore.DbContext class.

• Enter the following code:

  using Microsoft.EntityFrameworkCore;
  
  namespace TodoApi.Models;
  
  public class TodoContext : DbContext
  {
      public TodoContext(DbContextOptions<TodoContext> options)
          : base(options)
      {
      }
  
      public DbSet<TodoItem> TodoItems { get; set; } = null!;
  }
  

In ASP.NET Core, services such as the DB context must be registered with the dependency injection (DI) container. The container provides the service to controllers.

Update Program.cs with the following highlighted code:

using Microsoft.EntityFrameworkCore;
using TodoApi.Models;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddDbContext<TodoContext>(opt =>
    opt.UseInMemoryDatabase("TodoList"));
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

The preceding code:

• Adds using directives.
• Adds the database context to the DI container.
• Specifies that the database context will use an in-memory database.

dotnet add package Microsoft.VisualStudio.Web.CodeGeneration.Design
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
dotnet add package Microsoft.EntityFrameworkCore.Tools
dotnet tool uninstall -g dotnet-aspnet-codegenerator
dotnet tool install -g dotnet-aspnet-codegenerator
dotnet tool update -g dotnet-aspnet-codegenerator

echo 'export PATH=$HOME/.dotnet/tools:$PATH' >> ~/.bashrc
source ~/.bashrc

dotnet aspnet-codegenerator controller -name TodoItemsController -async -api -m TodoItem -dc TodoContext -outDir Controllers

The generated code:

• Marks the class with the [ApiController] attribute. This attribute indicates that the controller responds to web API requests. For information about specific behaviors that the attribute enables, see Create web APIs with ASP.NET Core.
• Uses DI to inject the database context (TodoContext) into the controller. The database context is used in each of the CRUD methods in the controller.

The ASP.NET Core templates for:

• Controllers with views include [action] in the route template.
• API controllers don't include [action] in the route template.

When the [action] token isn't in the route template, the action name (method name) isn't included in the endpoint. That is, the action's associated method name isn't used in the matching route.

Update the return statement in the PostTodoItem to use the nameof operator:

[HttpPost]
public async Task<ActionResult<TodoItem>> PostTodoItem(TodoItem todoItem)
{
    _context.TodoItems.Add(todoItem);
    await _context.SaveChangesAsync();

    //    return CreatedAtAction("GetTodoItem", new { id = todoItem.Id }, todoItem);
    return CreatedAtAction(nameof(GetTodoItem), new { id = todoItem.Id }, todoItem);
}

The preceding code is an HTTP POST method, as indicated by the [HttpPost] attribute. The method gets the value of the TodoItem from the body of the HTTP request.

For more information, see Attribute routing with Http[Verb] attributes.

The CreatedAtAction method:

• Returns an HTTP 201 status code if successful. HTTP 201 is the standard response for an HTTP POST method that creates a new resource on the server.
• Adds a Location header to the response. The Location header specifies the URI of the newly created to-do item. For more information, see 10.2.2 201 Created.
• References the GetTodoItem action to create the Location header's URI. The C# nameof keyword is used to avoid hard-coding the action name in the CreatedAtAction call.

• Press Ctrl+F5 to run the app.

• In the Swagger browser window, select POST /api/TodoItems, and then select Try it out.

• In the Request body input window, update the JSON. For example,

  {
    "name": "walk dog",
    "isComplete": true
  }
  

• Select Execute

  

In the preceding POST, the Swagger UI shows the location header under Response headers. For example, location: https://localhost:7260/api/TodoItems/1. The location header shows the URI to the created resource.

To test the location header:

• In the Swagger browser window, select GET /api/TodoItems/{id}, and then select Try it out.

• Enter 1 in the id input box, and then select Execute.

  

Two GET endpoints are implemented:

• GET /api/todoitems
• GET /api/todoitems/{id}

The previous section showed an example of the /api/todoitems/{id} route.

Follow the POST instructions to add another todo item, and then test the /api/todoitems route using Swagger.

This app uses an in-memory database. If the app is stopped and started, the preceding GET request doesn't return any data. If no data is returned, POST data to the app.

The [HttpGet] attribute denotes a method that responds to an HTTP GET request. The URL path for each method is constructed as follows:

• Start with the template string in the controller's Route attribute:

  [Route("api/[controller]")]
  [ApiController]
  public class TodoItemsController : ControllerBase
  

• Replace [controller] with the name of the controller, which by convention is the controller class name minus the "Controller" suffix. For this sample, the controller class name is TodoItemsController, so the controller name is "TodoItems". ASP.NET Core routing is case insensitive.

• If the [HttpGet] attribute has a route template (for example, [HttpGet("products")]), append that to the path. This sample doesn't use a template. For more information, see Attribute routing with Http[Verb] attributes.

In the following GetTodoItem method, "{id}" is a placeholder variable for the unique identifier of the to-do item. When GetTodoItem is invoked, the value of "{id}" in the URL is provided to the method in its id parameter.

[HttpGet("{id}")]
public async Task<ActionResult<TodoItem>> GetTodoItem(long id)
{
    var todoItem = await _context.TodoItems.FindAsync(id);

    if (todoItem == null)
    {
        return NotFound();
    }

    return todoItem;
}

The return type of the GetTodoItems and GetTodoItem methods is ActionResult<T> type. ASP.NET Core automatically serializes the object to JSON and writes the JSON into the body of the response message. The response code for this return type is 200 OK, assuming there are no unhandled exceptions. Unhandled exceptions are translated into 5xx errors.

ActionResult return types can represent a wide range of HTTP status codes. For example, GetTodoItem can return two different status values:

• If no item matches the requested ID, the method returns a 404 status NotFound error code.
• Otherwise, the method returns 200 with a JSON response body. Returning item results in an HTTP 200 response.

Examine the PutTodoItem method:

[HttpPut("{id}")]
public async Task<IActionResult> PutTodoItem(long id, TodoItem todoItem)
{
    if (id != todoItem.Id)
    {
        return BadRequest();
    }

    _context.Entry(todoItem).State = EntityState.Modified;

    try
    {
        await _context.SaveChangesAsync();
    }
    catch (DbUpdateConcurrencyException)
    {
        if (!TodoItemExists(id))
        {
            return NotFound();
        }
        else
        {
            throw;
        }
    }

    return NoContent();
}

PutTodoItem is similar to PostTodoItem, except it uses HTTP PUT. The response is 204 (No Content). According to the HTTP specification, a PUT request requires the client to send the entire updated entity, not just the changes. To support partial updates, use HTTP PATCH.

This sample uses an in-memory database that must be initialized each time the app is started. There must be an item in the database before you make a PUT call. Call GET to ensure there's an item in the database before making a PUT call.

Using the Swagger UI, use the PUT button to update the TodoItem that has Id = 1 and set its name to "feed fish". Note the response is HTTP 204 No Content.

Examine the DeleteTodoItem method:

[HttpDelete("{id}")]
public async Task<IActionResult> DeleteTodoItem(long id)
{
    var todoItem = await _context.TodoItems.FindAsync(id);
    if (todoItem == null)
    {
        return NotFound();
    }

    _context.TodoItems.Remove(todoItem);
    await _context.SaveChangesAsync();

    return NoContent();
}

Use the Swagger UI to delete the TodoItem that has Id = 1. Note the response is HTTP 204 No Content.

There are many other tools that can be used to test web APIs, for example:

• Visual Studio Endpoints Explorer and .http files
• http-repl
• curl. Swagger uses curl and shows the curl commands it submits.
• Fiddler

For more information, see:

• Minimal API tutorial: test with .http files and Endpoints Explorer

Currently the sample app exposes the entire TodoItem object. Production apps typically limit the data that's input and returned using a subset of the model. There are multiple reasons behind this, and security is a major one. The subset of a model is usually referred to as a Data Transfer Object (DTO), input model, or view model. DTO is used in this tutorial.

A DTO may be used to:

• Prevent over-posting.
• Hide properties that clients are not supposed to view.
• Omit some properties in order to reduce payload size.
• Flatten object graphs that contain nested objects. Flattened object graphs can be more convenient for clients.

To demonstrate the DTO approach, update the TodoItem class to include a secret field:

namespace TodoApi.Models
{
    public class TodoItem
    {
        public long Id { get; set; }
        public string? Name { get; set; }
        public bool IsComplete { get; set; }
        public string? Secret { get; set; }
    }
}

The secret field needs to be hidden from this app, but an administrative app could choose to expose it.

Verify you can post and get the secret field.

Create a DTO model:

namespace TodoApi.Models;

public class TodoItemDTO
{
    public long Id { get; set; }
    public string? Name { get; set; }
    public bool IsComplete { get; set; }
}

Update the TodoItemsController to use TodoItemDTO:

using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using TodoApi.Models;

namespace TodoApi.Controllers;

[Route("api/[controller]")]
[ApiController]
public class TodoItemsController : ControllerBase
{
    private readonly TodoContext _context;

    public TodoItemsController(TodoContext context)
    {
        _context = context;
    }

    // GET: api/TodoItems
    [HttpGet]
    public async Task<ActionResult<IEnumerable<TodoItemDTO>>> GetTodoItems()
    {
        return await _context.TodoItems
            .Select(x => ItemToDTO(x))
            .ToListAsync();
    }

    // GET: api/TodoItems/5
    // <snippet_GetByID>
    [HttpGet("{id}")]
    public async Task<ActionResult<TodoItemDTO>> GetTodoItem(long id)
    {
        var todoItem = await _context.TodoItems.FindAsync(id);

        if (todoItem == null)
        {
            return NotFound();
        }

        return ItemToDTO(todoItem);
    }
    // </snippet_GetByID>

    // PUT: api/TodoItems/5
    // To protect from overposting attacks, see https://go.microsoft.com/fwlink/?linkid=2123754
    // <snippet_Update>
    [HttpPut("{id}")]
    public async Task<IActionResult> PutTodoItem(long id, TodoItemDTO todoDTO)
    {
        if (id != todoDTO.Id)
        {
            return BadRequest();
        }

        var todoItem = await _context.TodoItems.FindAsync(id);
        if (todoItem == null)
        {
            return NotFound();
        }

        todoItem.Name = todoDTO.Name;
        todoItem.IsComplete = todoDTO.IsComplete;

        try
        {
            await _context.SaveChangesAsync();
        }
        catch (DbUpdateConcurrencyException) when (!TodoItemExists(id))
        {
            return NotFound();
        }

        return NoContent();
    }
    // </snippet_Update>

    // POST: api/TodoItems
    // To protect from overposting attacks, see https://go.microsoft.com/fwlink/?linkid=2123754
    // <snippet_Create>
    [HttpPost]
    public async Task<ActionResult<TodoItemDTO>> PostTodoItem(TodoItemDTO todoDTO)
    {
        var todoItem = new TodoItem
        {
            IsComplete = todoDTO.IsComplete,
            Name = todoDTO.Name
        };

        _context.TodoItems.Add(todoItem);
        await _context.SaveChangesAsync();

        return CreatedAtAction(
            nameof(GetTodoItem),
            new { id = todoItem.Id },
            ItemToDTO(todoItem));
    }
    // </snippet_Create>

    // DELETE: api/TodoItems/5
    [HttpDelete("{id}")]
    public async Task<IActionResult> DeleteTodoItem(long id)
    {
        var todoItem = await _context.TodoItems.FindAsync(id);
        if (todoItem == null)
        {
            return NotFound();
        }

        _context.TodoItems.Remove(todoItem);
        await _context.SaveChangesAsync();

        return NoContent();
    }

    private bool TodoItemExists(long id)
    {
        return _context.TodoItems.Any(e => e.Id == id);
    }

    private static TodoItemDTO ItemToDTO(TodoItem todoItem) =>
       new TodoItemDTO
       {
           Id = todoItem.Id,
           Name = todoItem.Name,
           IsComplete = todoItem.IsComplete
       };
}

Verify you can't post or get the secret field.

See Tutorial: Call an ASP.NET Core web API with JavaScript.

See Video: Beginner's Series to: Web APIs.

For guidance on creating a reliable, secure, performant, testable, and scalable ASP.NET Core app, see Enterprise web app patterns. A complete production-quality sample web app that implements the patterns is available.

ASP.NET Core Identity adds user interface (UI) login functionality to ASP.NET Core web apps. To secure web APIs and SPAs, use one of the following:

• Microsoft Entra ID
• Azure Active Directory B2C (Azure AD B2C)
• Duende Identity Server

Duende Identity Server is an OpenID Connect and OAuth 2.0 framework for ASP.NET Core. Duende Identity Server enables the following security features:

• Authentication as a Service (AaaS)
• Single sign-on/off (SSO) over multiple application types
• Access control for APIs
• Federation Gateway

For more information, see the Duende Identity Server documentation (Duende Software website).

For information on deploying to Azure, see Quickstart: Deploy an ASP.NET web app.

View or download sample code for this tutorial. See how to download.

For more information, see the following resources:

• Create web APIs with ASP.NET Core
• Tutorial: Create a minimal API with ASP.NET Core
• ASP.NET Core web API documentation with Swagger / OpenAPI
• Razor Pages with Entity Framework Core in ASP.NET Core - Tutorial 1 of 8
• Routing to controller actions in ASP.NET Core
• Controller action return types in ASP.NET Core web API
• Deploy ASP.NET Core apps to Azure App Service
• Host and deploy ASP.NET Core
• Create a web API with ASP.NET Core