Rest Basics

REST Introduction and REST Architecture

• Definition of REST:
  • REST stands for Representational State Transfer.
  • Understanding each term:
    • State: Represents data.
    • Representational: Denotes a data format (e.g., XML, JSON, YAML, HTML, plain text).
    • Transfer: Involves transferring data between consumer and provider using HTTP protocol.
• REST Architecture Overview:
  • Involves a client-server model where a client sends HTTP requests to a server, and the server processes and responds.
  • Clients can be diverse (e.g., Android, iOS, desktop, web applications).
  • Independence: Client and server should be independent; changes in one shouldn’t affect the other.
  • Message Exchange Format: Data exchanged between client and server typically in JSON or XML.
• Key Points about REST:
  • Origin: Coined by Roy Fielding, inventor of HTTP protocol.
  • Purpose: Facilitates communication between applications over HTTP, akin to browser-server interaction.
  • Popularity: Rapid adoption due to increased mobile device usage, allowing web and mobile clients to consume the same APIs.
• REST Architectural Constraints:
  • Client-Server Architecture: Client and server are distinct, independent components.
  • Statelessness: No session data stored on the server; each request is stateless.
  • Cacheability: Clients can cache responses for improved performance.
  • Uniform Interface: Provides a consistent, generic interface for interactions, simplifying architecture.
  • Layered System: Servers can have multiple layers for scalability and load balancing.
  • Code on Demand (Optional): Allows clients to download and execute code from the server, though rarely used.
• Conclusion:
  • RESTful APIs follow these architectural constraints to ensure effective communication between clients and servers.

Key Terms:

• REST
• Representational State Transfer
• State
• Representational
• Transfer
• HTTP protocol
• Client
• Server
• Web services
• HTTP request
• HTTP response
• Message Exchange Format
• JSON
• XML
• Roy Fielding
• Client-server architecture
• Independence
• Statelessness
• Cacheability
• Uniform Interface
• Layered System
• Code on Demand

REST Key Concepts - Resource, URI and Sub-resource

Notes on REST Key Concepts:

• Resource in REST:
  • In a REST-based system, everything is a resource.
  • A resource is anything exposed to the outside world through the application.
  • Examples of resources in various systems: Employee, Department, Address, Project, Task (Employee Management System); Student, Teacher, Class, Subject, School (Student Management System); Post, Comment, User, Tags, Category (Blog Application).
  • CRUD (Create, Read, Update, Delete) REST APIs are typically created for each resource.
  • Clients consume these REST APIs to perform actions on resources.
• Uniform Resource Identifier (URI):
  • URI is used to identify resources.
  • Each URI should be unique.
  • Examples of URIs for CRUD operations on a Post resource:
    • URL to list posts
    • URL to retrieve a post by ID
    • URL to create a new post
    • URL to update a post
    • URL to delete a post
• Sub-resource:
  • Sub-resources are used to model relationships in REST APIs.
  • Relationships are modeled by placing a sub-resource after a resource.
  • Pattern: resource/resource-id/sub-resource/sub-resource-id.
  • Example: In a blog application, posts can have comments as sub-resources. To retrieve comments for a particular post, the URI would be post/post-id/comments.
  • Sub-resources are used when child objects cannot exist without their parent (e.g., comments cannot exist without a post, drivers cannot exist without a car).
  • Deleting the parent resource may also delete the associated sub-resources.

Key Terms:

• Resource
• CRUD
• Uniform Resource Identifier (URI)
• Sub-resource
• Relationships
• Parent-child relationship
• HTTP Methods
• HTTP Status Codes

REST Key Concepts - Http Methods

Notes on HTTP Methods in RESTful Web Services:

• HTTP Methods:
  • GET: Used to retrieve or get a collection or a single resource. Not for modifying or creating resources.
  • POST: Utilized to create a new resource. Typically used for adding new entities like employees, students, or users.
  • PUT: Employed to update an existing resource. Used when modifying existing entities such as updating employee details or student information.
  • DELETE: Used to delete a collection or a single resource. Enables removal of entities like students or specific records identified by their unique identifiers.
  • PATCH: Optionally used to partially update an existing resource.
• Usage Examples:
  • GET Method: Retrieve a list of posts or a single post by ID.
  • POST Method: Create a new post in a blog application.
  • PUT Method: Update an existing post by specifying its ID.
  • DELETE Method: Delete a post or other resources by their IDs.
• Additional Note:
  • PATCH Method: Used for partial updates to existing resources, updating specific fields without modifying the entire resource.

Key Terms:

• HTTP Methods
• GET
• POST
• PUT
• DELETE
• PATCH
• RESTful Web Services
• Resource Modification
• Resource Creation
• Resource Deletion
• Postman

REST Key Concepts - HTTP Status Codes

Notes on Important HTTP Status Codes:

• Overview:
  • HTTP status codes indicate the outcome of a request made by a client to a server.
  • These status codes help in understanding the status of the request and guide further actions.
• 200 OK:
  • Indicates: Request is successful, and response content is returned to the client as appropriate.
  • Example: Retrieving a collection of blog posts or a single post.
• 201 CREATED:
  • Indicates: Request is successful, and a new resource is created.
  • Example: Creating a new blog post; server responds with the newly created resource.
• 400 Bad Request:
  • Indicates: Server failed to process the request due to malformed syntax in the request.
  • Example: Client passed invalid parameters; server responds with a bad request status code.
• 401 Unauthorized:
  • Indicates: Authentication is required for the resource, and the client needs to provide appropriate credentials.
  • Example: Accessing a protected resource without valid authentication; server responds with an unauthorized status code.
• 403 Forbidden:
  • Indicates: Server refuses to respond to the request, even if the request is valid.
  • Example: Attempting to access unauthorized resources; server responds with a forbidden status code.
• 404 Not Found:
  • Indicates: Requested resource is not found at the specified location.
  • Example: Attempting to delete a blog post that does not exist; server responds with a not found status code.
• 500 Internal Server Error:
  • Indicates: An unexpected error occurred on the server, and the request cannot be fulfilled.
  • Example: Server-side error during user authentication or other processing; server responds with an internal server error status code.

Key Terms:

• HTTP Status Codes
• 200 OK
• 201 CREATED
• 400 Bad Request
• 401 Unauthorized
• 403 Forbidden
• 404 Not Found
• 500 Internal Server Error
• Client-Server Communication