BEAUTIFUL REST APIsin ASP.NET Core

Nate Barbettini@nbarbettini

recaffeinate.co .ws

Overview

● Why is API design important?● HATEOAS (Hypertext As The Engine Of Application State)● REST APIs in ASP.NET Core

/getAccount?id=17

Bad REST API design

/getAccount?all=1&includePosts=1

/getAllAccounts

/updateAccount?id=17

/createAccount

/findPostsByAccountId?account=17

/accountSearch?lname=Skywalker

/getAccount?id=17&includePosts=1

/getAccount?id=17&format=json

/getAllAccountsJson

/updateAccount?id=17&return=json

/createAccountJson

/accountSearch?lname=Skywalker&xml=1

/findPostsByAccountIdJSON?account=17

/getAllPosts?filter=account&id=17

/countAccounts

/partialUpdateAccount?id=17

/getPostCount?id=17

/deleteUser

HATEOAS, yo!"A REST API should be entered with no prior knowledge beyond the initial URI (bookmark) and set of standardized media types that are appropriate for the intended audience (i.e., expected to be understood by any client that might use the API). From that point on, all application state transitions must be driven by client selection of server-provided choices that are present in the received representations or implied by the user’s manipulation of those representations." ~ Dr. Fielding

Tl;dr The API responses themselves should document what you are allowed to do and where you can go.

If you can get to the root (/), you should be able to “travel” anywhere else in the API.

Good REST API design should...● Be discoverable and self-documenting● Represent resources and collections● Represent actions using HTTP verbs● KISS!

Revisiting the API example

/users GET: List all usersPOST or PUT: Create a user

/users/17 GET: Retrieve a single userPOST or PUT: Update user detailsDELETE: Delete this user

/users/17/posts GET: Get the user’s postsPOST: Create a post

/users?lname=SkywalkerSearch

/users/17?include=postsInclude linked data

A specification for REST+JSON APIs

The ION spec: https://github.com/ionwg/ion-doc

Getting a single userGET /users/17

{ "meta": { "href": "https://example.io/users/17" }, "firstName": "Luke", "lastName": "Skywalker"}

Getting a list of usersGET /users

{ "meta": { "href": "https://example.io/users", "rel": ["collection"] }, "items": [{

"meta": { "href": "https://example.io/users/17" }, "firstName": "Luke", "lastName": "Skywalker"}, { "meta": { "href": "https://example.io/users/18" }, "firstName": "Han", "lastName": "Solo"}]

}

Discoverable formsGET /users

{ ...

"create": { "meta": { "href": "https://example.io/users", "rel": ["create-form"], "method": "post" }, "items": [ { "name": "firstName" }, { "name": "lastName" } ] }}

Discoverable searchGET /users

{ ...

"search": { "meta": { "href": "https://example.io/users", "rel": ["search-form"], "method": "get" }, "items": [ { "name": "fname" }, { "name": "lname" } ] }}

The starting point (API root)GET /

{ "meta": { "href": "https://example.io/" }, "users": { "meta": { "href": "https://example.io/users", "rel": ["collection"], } }}

● Install the .NET Core SDK - http://dot.net/core● If you’re using Visual Studio:

○ Install the latest updates (Update 3)○ Install the .NET Core tooling - https://go.microsoft.com/fwlink/?LinkID=824849

● Or, install Visual Studio Code● Create a new project from the ASP.NET Core (.NET Core) template● Pick the API subtemplate● Ready to run!

Getting started with ASP.NET Core

Getting a single userGET /users/17

{ "meta": { "href": "https://example.io/users/17" }, "firstName": "Luke", "lastName": "Skywalker"}

public class Link{ public string Href { get; set; }}

public abstract class Resource{ [JsonProperty(Order = -2)] public Link Meta { get; set; }}

Getting a single user

public class User : Resource{ public string FirstName { get; set; }

public string LastName { get; set; }}

Getting a single user

[Route("/users")]public class UsersController : Controller{ private readonly BulletinBoardDbContext _context; private readonly IUrlHelperFactory _urlHelperFactory;

public UsersController( BulletinBoardDbContext context, IUrlHelperFactory urlHelperFactory) { _context = context; _urlHelperFactory = urlHelperFactory; }

Getting a single user

[Route("{id}")]public async Task<IActionResult> GetUser(string id){ var user = await _context.Users.SingleOrDefaultAsync(x => x.Id == id); if (user == null) return NotFound();

var urlHelper = _urlHelperFactory.GetUrlHelper(ControllerContext); var url = urlHelper.Link("default", new { controller = "users", id = user.Id });

var response = new User() { Meta = new Link() { Href = url }, FirstName = user.FirstName, LastName = user.LastName };

return Ok(response);}

Getting a single user

Getting a list of usersGET /users

{ "meta": { "href": "https://example.io/users", "rel": ["collection"] }, "items": [{

"meta": { "href": "https://example.io/users/17" }, "firstName": "Luke", "lastName": "Skywalker"}, { "meta": { "href": "https://example.io/users/18" }, "firstName": "Han", "lastName": "Solo"}]

}

Getting a list of userspublic class Link{ public string Href { get; set; }

[JsonProperty(PropertyName = "rel", NullValueHandling = NullValueHandling.Ignore)] public string[] Relations { get; set; }}

Getting a list of userspublic class Collection<T> : Resource{ public T[] Items { get; set; }}

Getting a list of userspublic async Task<IActionResult> GetAll(){ var urlHelper = _urlHelperFactory.GetUrlHelper(ControllerContext); var allUsers = await _context.Users.ToArrayAsync();

var projected = allUsers.Select(x => new User() { Meta = new Link() { Href = urlHelper.Link("default", new { controller = "users", id = x.Id }) }, FirstName = x.FirstName, LastName = x.LastName });

var response = new Collection<User>() { Meta = new Link() { Href = urlHelper.Link("default", new { controller = "users" }), Relations = new string[] {"collection"}, }, Items = projected.ToArray() }; return Ok(response);}

The starting point (API root)GET /

{ "meta": { "href": "https://example.io/" }, "users": { "meta": { "href": "https://example.io/users", "rel": ["collection"], } }}

Adding a root route[Route("/")]public class RootController : Controller{ private readonly IUrlHelperFactory _urlHelperFactory; public RootController(IUrlHelperFactory urlHelperFactory) { _urlHelperFactory = urlHelperFactory; }

public IActionResult Get() { var urlHelper = _urlHelperFactory.GetUrlHelper(ControllerContext); var response = new { meta = new Link() { Href = urlHelper.Link("default", new { controller = "root" }) }, users = new Link() { Href = urlHelper.Link("default", new { controller = "users" }), Relations = new string[] {"collection"} } }; return Ok(response); }}

Building and running (anywhere!)> dotnet build(...)Done.

> dotnet run(...)Listening on https://localhost:5000

Next Steps

● Full example

https://github.com/nbarbettini/beautiful-rest-api-aspnetcore

● ION draft spec

https://github.com/ionwg/ion-doc

Thank you!Nate Barbettini

@nbarbettinirecaffeinate.co .ws