# 5. REST Architecture

# HTTP Methods for RESTful APIs

* You have so far implemented GET and POST methods for reading resources from the API and creating new ones to it
* All the primary methods for following the uniform interface requirement are  __GET, POST, PUT, PATCH __ and  __DELETE__
  * Others exist, but these are by far most commonly used
* These methods correspond to  __CRUD __ operations  __Create__ ,  __Read__ ,  __Update __ and  __Delete__
* CRUD describes what is done to a resource after a request is sent

# HTTP Methods for RESTful APIs (continued)

The primary HTTP request methods with descriptions:

| __Method__ | __Attribute__ | __Description__ |
| :-: | :-: | :-: |
| GET | [HttpGet] | _Read _ a representation of a resource |
| POST | [HttpPost] | _Create _ new resources |
| PUT | [HttpPut] | Fully  _Update _ an existing resource |
| PATCH | [HttpPatch] | Partially  _Update _ an existing resource |
| DELETE | [HttpDelete] | _Delete _ a resource |

[https://www.restapitutorial.com/lessons/httpmethods.html](https://www.restapitutorial.com/lessons/httpmethods.html)

# Handling HttpPost Requests

Remember, that HTTP requests can include a content body

In ASP.NET, this content is assigned to a variable with the [FromBody] attribute:

[HttpPost]

public string[] Post([FromBody] string someContent)

{

// someContent holds the content of the request body

return new string[] { text };

}

Note that the [FromBody] attribute can only be used on one parameter

However, nothing prevents you from using a custom type variable

# Handling HttpPost Requests (continued)

ASP.NET deserializes the request content body into an object:

public class Student

{

public int Id { get; set; }

public string Name { get; set; }

}

// In controller class:

[HttpPost]

public Contact Put(int id, [FromBody] Contact contact)

{

// Contacts = list of Contact objects, fetched from some repository

Contacts.Add(contact);

return contact;

}

# Creating a POST Request with Postman

* ASP.NET knows to deserialize the content if the content type is set to JSON in the HTTP requests  __headers__
  * Headers are optional parameters that can be included in every HTTP request
  * Headers are set in Key-Value format
  * When creating a request in Postman, to inform the server what type of content was just sent, add a new key "Content-Type" and set its value to "application/json" in the  _Headers _ tab:

![](imgs/5-rest-architecture_1.png)

# Creating a POST Request with Postman (continued)

After setting the header,

select the Body tab,

change the content type to raw,

select JSON from the dropdown menu, and

insert the content in JSON format

![](imgs/5-rest-architecture_2.png)

# Creating a POST Request with Postman - Example

Suppose the Post method from before is routed at http://localhost:54106/api/students:

![](imgs/5-rest-architecture_3.png)

# Exercise 1: Creating a POST Endpoint

Continue working on CourseAPI.

Create a Post method and endpoint which adds a new course to the list in the repository, with a running ID. Content and Author values are obtained from the request body:

![](imgs/5-rest-architecture_4.png)

# HTTP PUT

Use PUT to replace an existing resource, e.g. an element in a list, with a new one

The ID of the resource to be replaced should be in the request URI

The information about the new resource should be in the request body like in POST requests

![](imgs/5-rest-architecture_5.png)

# Handling HttpPut Requests

The ID is fetched from the URI and the contents from the request body

Filtering is used to copy all objects from the original list except for the new contact object, which comes from body

[HttpPut("{id}")]

public List<Contact> Put(int id, [FromBody] Contact contact)

{

// Contacts = list of Contact objects, fetched from some repository

List<Contact> updatedList = Contacts.Select(c => c.Id != id ? c : contact).ToList();

Contacts = updatedList;

return updatedList;

}

# Exercise 2: Creating a PUT Endpoint

* In CoursesController class, create a method for PUT requests with the URI api/courses/{id}
  * The ID of the course to be replaced with should be in the request URI and the contents of the new course should be in the request body.
  * The method should replace the corresponding course from the Courses list in the repository with the new course.
  * The method should return the updated Courses list (for testing purposes)
  * Return a 404 status code if a course with the corresponding ID does not exist
* Test with Swagger/Postman

# HTTP DELETE

Use DELETE to delete an existing resource, e.g. an element in a list

The ID of the resource to be deleted should be in the request URI

As with GET method, a body is not needed

![](imgs/5-rest-architecture_6.png)

# Handling HttpDelete Requests

The ID is fetched from the URI

[HttpDelete("{id}")]

public List<Contact> Delete(int id)

{

// Contacts = list of contact objects, fetched from some repository

List<Contact> updatedList = Contacts.Where(c => c.Id != id).ToList();

Contacts = updatedList;

return Contacts;

}

# Exercise 3: Creating a DELETE Endpoint

* Continue working on CourseAPI.
* Create an endpoint for DELETE requests with the URI api/courses/{id}
  * The ID of the course should be fetched from the URI
  * The corresponding course should be removed from the list of courses in the repository
  * The method should return the updated Courses list (for testing purposes)
  * Return a 404 status code if a course with the corresponding ID does not exist
* Test with Postman

# HTTP PATCH

* Use PATCH to partially update a resource
  * I.e. update some value inside of a resource
  * This saves some resources as only a part of a resource has to be sent instead of an entire document (as opposed to PUT requests)
* Sending and handling PATCH requests with ASP.NET requires some extra work and the use of a third party package:  [http://jsonpatch.com/](http://jsonpatch.com/)

# HTTP PATCH (continued)

* To handle PATCH requests in a standardized way, install and add the following NuGet packages to your project:
  * Microsoft.AspNetCore.JsonPatch
  * Microsoft.AspNetCore.Mvc.NewtonsoftJson
* Then, change the following line in Program.cs (ASP.NET 5: Startup.cs)...
* builder.Services.AddControllers();
* … to this:
* builder.Services.AddControllers().AddNewtonsoftJson();

The  body of the PATCH request needs to be in the following form:

[{ "op": "replace", "path": "/propertyName", "value": "newValue"}]

Use the URI to specify the ID of the resource to update

![](imgs/5-rest-architecture_7.png)

# Handling HttpPatch Requests

The ID is fetched from the URI

The property and its new value are specified in the body, which is retrieved as JsonPatchDocument

PATCH is operated on the targeted object

[HttpPatch("{id}")]

public List<Contact> Patch(int id, [FromBody] JsonPatchDocument<Contact> patchDocument)

{

// Contacts = list of contact objects, fetched from some repository

var contact = Contacts.FirstOrDefault(c => c.Id == id);

if(contact != null){

patchDocument.ApplyTo(contact);

}

return Contacts;

}

# Exercise 4: Creating a PATCH Endpoint

* Continue working on CourseAPI.
* Create an endpoint for PATCH requests with the URI api/courses/{id}
  * The ID of the course should be fetched from the URI
  * The corresponding course should be updated according to the JSON PATCH document in the request body
  * The method should return the updated Courses list (for testing purposes)
  * Return a 404 status code if a course with the corresponding ID does not exist
* Test with Swagger/Postman: try to change the number of credits for some course
