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title	author	description	ms.author	ms.date	ms.custom	monikerRange	uid
Tutorial: Create a minimal API with ASP.NET Core	wadepickett	Learn how to build a minimal API with ASP.NET Core.	wpickett	02/22/2024	engagement-fy24	>= aspnetcore-6.0	tutorials/min-web-api

Tutorial: Create a minimal API with ASP.NET Core

[!INCLUDE]

By Rick Anderson and Tom Dykstra

:::moniker range=">= aspnetcore-8.0"

Minimal APIs are architected to create HTTP APIs with minimal dependencies. They are ideal for microservices and apps that want to include only the minimum files, features, and dependencies in ASP.NET Core.

This tutorial teaches the basics of building a minimal API with ASP.NET Core. Another approach to creating APIs in ASP.NET Core is to use controllers. For help with choosing between minimal APIs and controller-based APIs, see xref:fundamentals/apis. For a tutorial on creating an API project based on controllers that contains more features, see Create a web API.

Overview

This tutorial creates the following API:

API	Description	Request body	Response body
`GET /todoitems`	Get all to-do items	None	Array of to-do items
`GET /todoitems/complete`	Get completed to-do items	None	Array of to-do items
`GET /todoitems/{id}`	Get an item by ID	None	To-do item
`POST /todoitems`	Add a new item	To-do item	To-do item
`PUT /todoitems/{id}`	Update an existing item	To-do item	None
`DELETE /todoitems/{id}`	Delete an item	None	None

Prerequisites

Visual Studio

[!INCLUDE]

Visual Studio Code

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Visual Studio for Mac

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Create an API project

Visual Studio

Start Visual Studio 2022 Preview and select Create a new project.
In the Create a new project dialog:
- Enter Empty in the Search for templates search box.
- Select the ASP.NET Core Empty template and select Next.
Name the project TodoApi and select Next.
In the Additional information dialog:
- Select .NET 8.0 (Long Term Support)
- Uncheck Do not use top-level statements
- Select Create

Visual Studio Code

Open the integrated terminal.
Change directories (cd) to the folder that will contain the project folder.

Run the following commands:

dotnet new web -o TodoApi
cd TodoApi
code -r ../TodoApi

When a dialog box asks if you want to trust the authors, select Yes.
When a dialog box asks if you want to add required assets to the project, select Yes.

The preceding commands create a new web minimal API project and open it in Visual Studio Code.

Visual Studio for Mac

In Visual Studio for Mac 2022, select File > New Project....
In the Choose a template for your new project dialog:
- Select Web and Console > App > Empty
- Select Continue
Make the following selections:
- Target framework: .NET 8.0
- Configure for HTTPS: Check
- Do not use top-level statements: Uncheck
- Select Continue
Enter the following:
- Project name: TodoApi
- Solution name: TodoApi
- Select Create

Examine the code

The Program.cs file contains the following code:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todo/Program.cs" id="snippet_min":::

The preceding code:

Creates a xref:Microsoft.AspNetCore.Builder.WebApplicationBuilder and a xref:Microsoft.AspNetCore.Builder.WebApplication with preconfigured defaults.
Creates an HTTP GET endpoint / that returns Hello World!:

Run the app

Visual Studio

Press Ctrl+F5 to run without the debugger.

[!INCLUDE]

Visual Studio launches the Kestrel web server and opens a browser window.

Visual Studio Code

[!INCLUDE]

Press Ctrl+F5 to run the app. A browser window is opened.

Visual Studio for Mac

Select Debug > Start Debugging to launch the app. Visual Studio for Mac launches a browser and navigates to https://localhost:<port>, where <port> is a randomly chosen port number.

Hello World! is displayed in the browser. The Program.cs file contains a minimal but complete app.

Add NuGet packages

NuGet packages must be added to support the database and diagnostics used in this tutorial.

Visual Studio

From the Tools menu, select NuGet Package Manager > Manage NuGet Packages for Solution.
Select the Browse tab.
Enter Microsoft.EntityFrameworkCore.InMemory in the search box, and then select Microsoft.EntityFrameworkCore.InMemory.
Select the Project checkbox in the right pane and then select Install.
Follow the preceding instructions to add the Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore package.

Visual Studio Code

Run the following commands:

dotnet add package Microsoft.EntityFrameworkCore.InMemory
dotnet add package Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore

Visual Studio for Mac

In the Visual Studio for Mac 2022 toolbar, select Project > Manage NuGet Packages....
In the search box, enter Microsoft.EntityFrameworkCore.InMemory.
In the results window, check Microsoft.EntityFrameworkCore.InMemory.
Select Add Package.
In the Select Projects window, select Ok.
In the License Agreement window, select Agree.
Follow the preceding instructions to add the Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore package.

The model and database context classes

In the project folder, create a file named Todo.cs with the following code:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoGroup/Todo.cs":::

The preceding code creates the model for this app. A model is a class that represents data that the app manages.

Create a file named TodoDb.cs with the following code:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoGroup/TodoDb.cs":::

The preceding code defines the database context, which is the main class that coordinates Entity Framework functionality for a data model. This class derives from the xref:Microsoft.EntityFrameworkCore.DbContext?displayProperty=fullName class.

Add the API code

Replace the contents of the Program.cs file with the following code:

[!code-csharp]

The following highlighted code adds the database context to the dependency injection (DI) container and enables displaying database-related exceptions:

[!code-csharp]

The DI container provides access to the database context and other services.

Visual Studio

This tutorial uses Endpoints Explorer and .http files to test the API.

Visual Studio Code / Visual Studio for Mac

This tutorial uses Postman to test the API.

Install Postman to test the app

Install Postman
Start the web app.
Start Postman.
Select Workspaces > Create Workspace and then select Next.
Name the workspace TodoApi and select Create.
Select the settings gear icon > Settings (General tab) and disable SSL certificate verification.

[!WARNING] Re-enable SSL certificate verification after testing the sample app.

Test posting data

The following code in Program.cs creates an HTTP POST endpoint /todoitems that adds data to the in-memory database:

[!code-csharp]

Run the app. The browser displays a 404 error because there's no longer a / endpoint.

Use the POST endpoint to add data to the app.

Visual Studio

Select View > Other Windows > Endpoints Explorer.
Right-click the POST endpoint and select Generate request.

A new file is created in the project folder named TodoApi.http, with contents similar to the following example:
```
@TodoApi_HostAddress = https://localhost:7031

Post {{TodoApi_HostAddress}}/todoitems

###
```
- The first line creates a variable that is used for all of the endpoints.
- The next line defines a POST request.
- The triple hashtag (###) line is a request delimiter: what comes after it is for a different request.
The POST request needs headers and a body. To define those parts of the request, add the following lines immediately after the POST request line:
```
Content-Type: application/json

{
  "name":"walk dog",
  "isComplete":true
}
```
The preceding code adds a Content-Type header and a JSON request body. The TodoApi.http file should now look like the following example, but with your port number:
```
@TodoApi_HostAddress = https://localhost:7057

Post {{TodoApi_HostAddress}}/todoitems
Content-Type: application/json

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

###
```
Run the app.
Select the Send request link that is above the POST request line.

The POST request is sent to the app and the response is displayed in the Response pane.

Visual Studio Code / Visual Studio for Mac

In Postman, create a new HTTP request by selecting New > HTTP.
Set the HTTP method to POST.
Set the URI to https://localhost:<port>/todoitems. For example: https://localhost:5001/todoitems
Select the Body tab.
Select raw.
Set the type to JSON.

In the request body enter JSON for a to-do item:

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

Select Send.

Examine the GET endpoints

The sample app implements several GET endpoints by calling MapGet:

API	Description	Request body	Response body
`GET /todoitems`	Get all to-do items	None	Array of to-do items
`GET /todoitems/complete`	Get all completed to-do items	None	Array of to-do items
`GET /todoitems/{id}`	Get an item by ID	None	To-do item

[!code-csharp]

Test the GET endpoints

Visual Studio

Test the app by calling the GET endpoints from a browser or by using Endpoints Explorer. The following steps are for Endpoints Explorer.

In Endpoints Explorer, right-click the first GET endpoint, and select Generate request.

The following content is added to the TodoApi.http file:
```
Get {{TodoApi_HostAddress}}/todoitems

###
```
Select the Send request link that is above the new GET request line.

The GET request is sent to the app and the response is displayed in the Response pane.

The response body is similar to the following JSON:

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

In Endpoints Explorer, right-click the third GET endpoint and select Generate request. The following content is added to the TodoApi.http file:
```
GET {{TodoApi_HostAddress}}/todoitems/{id}

###
```
Replace {id} with 1.
Select the Send request link that is above the new GET request line.

The GET request is sent to the app and the response is displayed in the Response pane.

The response body is similar to the following JSON:

{
  "id": 1,
  "name": "walk dog",
  "isComplete": false
}

Visual Studio Code / Visual Studio for Mac

Test the app by calling the endpoints from a browser or Postman. The following steps are for Postman.

Create a new HTTP request.
Set the HTTP method to GET.
Set the request URI to https://localhost:<port>/todoitems. For example, https://localhost:5001/todoitems.
Select Send.

The call to GET /todoitems produces a response similar to the following:

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

Set the request URI to https://localhost:<port>/todoitems/1. For example, https://localhost:5001/todoitems/1.
Select Send.

The response is similar to the following:

{
  "id": 1,
  "name": "walk dog",
  "isComplete": false
}

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

Return values

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.

The return types can represent a wide range of HTTP status codes. For example, GET /todoitems/{id} can return two different status values:

If no item matches the requested ID, the method returns a 404 status xref:Microsoft.AspNetCore.Mvc.ControllerBase.NotFound%2A error code.
Otherwise, the method returns 200 with a JSON response body. Returning item results in an HTTP 200 response.

Examine the PUT endpoint

The sample app implements a single PUT endpoint using MapPut:

[!code-csharp]

This method is similar to the MapPost method, except it uses HTTP PUT. A successful response returns 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.

Test the PUT endpoint

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.

Update the to-do item that has Id = 1 and set its name to "feed fish".

Visual Studio

In Endpoints Explorer, right-click the PUT endpoint, and select Generate request.

The following content is added to the TodoApi.http file:
```
Put {{TodoApi_HostAddress}}/todoitems/{id}

###
```
In the PUT request line, replace {id} with 1.
Add the following lines immediately after the PUT request line:
```
Content-Type: application/json

{
  "id": 1,
  "name": "feed fish",
  "isComplete": false
}
```
The preceding code adds a Content-Type header and a JSON request body.
Select the Send request link that is above the new GET request line.

The PUT request is sent to the app and the response is displayed in the Response pane. The response body is empty, and the status code is 204.

Visual Studio Code / Visual Studio for Mac

Use Postman to send a PUT request:

Set the method to PUT.
Set the URI of the object to update (for example https://localhost:5001/todoitems/1).

Set the body to the following JSON:

{
  "id": 1,
  "name": "feed fish",
  "isComplete": false
}

Select Send.

Examine and test the DELETE endpoint

The sample app implements a single DELETE endpoint using MapDelete:

[!code-csharp]

Visual Studio

In Endpoints Explorer, right-click the DELETE endpoint and select Generate request.

A DELETE request is added to TodoApi.http.
Replace {id} in the DELETE request line with 1. The DELETE request should look like the following example:
```
DELETE {{TodoApi_HostAddress}}/todoitems/1

###
```
Select the Send request link for the DELETE request.

The DELETE request is sent to the app and the response is displayed in the Response pane. The response body is empty, and the status code is 204.

Visual Studio Code / Visual Studio for Mac

Use Postman to delete a to-do item:

Set the method to DELETE.
Set the URI of the object to delete (for example https://localhost:5001/todoitems/1).
Select Send.

Use the MapGroup API

The sample app code repeats the todoitems URL prefix each time it sets up an endpoint. APIs often have groups of endpoints with a common URL prefix, and the xref:Microsoft.AspNetCore.Builder.EndpointRouteBuilderExtensions.MapGroup%2A method is available to help organize such groups. It reduces repetitive code and allows for customizing entire groups of endpoints with a single call to methods like xref:Microsoft.AspNetCore.Builder.AuthorizationEndpointConventionBuilderExtensions.RequireAuthorization%2A and xref:Microsoft.AspNetCore.Builder.RoutingEndpointConventionBuilderExtensions.WithMetadata%2A.

Replace the contents of Program.cs with the following code:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoGroup/Program.cs" id="snippet_all":::

The preceding code has the following changes:

Adds var todoItems = app.MapGroup("/todoitems"); to set up the group using the URL prefix /todoitems.
Changes all the app.Map<HttpVerb> methods to todoItems.Map<HttpVerb>.
Removes the URL prefix /todoitems from the Map<HttpVerb> method calls.

Test the endpoints to verify that they work the same.

Use the TypedResults API

Returning xref:Microsoft.AspNetCore.Http.TypedResults rather than xref:Microsoft.AspNetCore.Http.Results has several advantages, including testability and automatically returning the response type metadata for OpenAPI to describe the endpoint. For more information, see TypedResults vs Results.

The Map<HttpVerb> methods can call route handler methods instead of using lambdas. To see an example, update Program.cs with the following code:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoTypedResults/Program.cs" id="snippet_all":::

The Map<HttpVerb> code now calls methods instead of lambdas:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoTypedResults/Program.cs" id="snippet_group":::

These methods return objects that implement xref:Microsoft.AspNetCore.Http.IResult and are defined by xref:Microsoft.AspNetCore.Http.TypedResults:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoTypedResults/Program.cs" id="snippet_handlers":::

Unit tests can call these methods and test that they return the correct type. For example, if the method is GetAllTodos:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoTypedResults/Program.cs" id="snippet_getalltodos":::

Unit test code can verify that an object of type Ok<Todo[]> is returned from the handler method. For example:

public async Task GetAllTodos_ReturnsOkOfTodosResult()
{
    // Arrange
    var db = CreateDbContext();

    // Act
    var result = await TodosApi.GetAllTodos(db);

    // Assert: Check for the correct returned type
    Assert.IsType<Ok<Todo[]>>(result);
}

Prevent over-posting

Currently the sample app exposes the entire Todo 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 article.

A DTO can be used to:

Prevent over-posting.
Hide properties that clients aren't 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 Todo class to include a secret field:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoDTO/Todo.cs":::

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 file named TodoItemDTO.cs with the following code:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoDTO/TodoItemDTO.cs":::

Update the code in Program.cs to use this DTO model:

:::code language="csharp" source="~/tutorials/min-web-api/samples/8.x/todoDTO/Program.cs" id="snippet_all":::

Verify you can post and get all fields except the secret field.

Troubleshooting with the completed sample

If you run into a problem you can't resolve, compare your code to the completed project. View or download completed project (how to download).

Next steps

Configure JSON serialization options.
Handle errors and exceptions: The developer exception page is enabled by default in the development environment for minimal API apps. For information about how to handle errors and exceptions, see Handle errors in ASP.NET Core APIs.
For an example of testing a minimal API app, see this GitHub sample.
OpenAPI support in minimal APIs.
Quickstart: Publish to Azure.
Organizing ASP.NET Core Minimal APIs

Learn more

See xref:fundamentals/minimal-apis

:::moniker-end

[!INCLUDE]

24 KiB Raw Blame History

Tutorial: Create a minimal API with ASP.NET Core

Overview

Prerequisites

Create an API project

Examine the code

Run the app

Add NuGet packages

The model and database context classes

Add the API code

Install Postman to test the app

Test posting data

Examine the GET endpoints

Test the GET endpoints

Return values

Examine the PUT endpoint

Test the PUT endpoint

Examine and test the DELETE endpoint

Use the MapGroup API

Use the TypedResults API

Prevent over-posting

Troubleshooting with the completed sample

Next steps

Learn more

24 KiB

Raw Blame History