🛠️ CRUD Controllers and RESTful API Design

In this lesson, we'll implement all the CRUD operations for our API resources. We'll explore how REST principles map HTTP verbs and routes to controller functions, creating a predictable and intuitive API interface.

Understanding CRUD Operations

CRUD is the foundation of most APIs - four basic operations that can be performed on any resource:

Operation	Purpose	HTTP Verb	Typical Route	Status Code
Create	Add new resource	POST	/api/resources	201 Created
Read	Fetch resource(s)	GET	/api/resources or /api/resources/:id	200 OK
Update	Modify resource	PUT/PATCH	/api/resources/:id	200 OK
Delete	Remove resource	DELETE	/api/resources/:id	200 OK or 204 No Content

RESTful Route Design

REST (Representational State Transfer) provides conventions for API design:

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REST Principles:

Resources as URLs: /api/habits represents the habits collection
HTTP Verbs as Actions: GET reads, POST creates, PUT updates, DELETE removes
Stateless: Each request contains all information needed
Consistent Patterns: Predictable URL structures across resources </aside>

Route + Verb = Controller Function

// The router literally maps verb + path to a function
router.get('/habits', getUserHabits)        // GET /api/habits
router.get('/habits/:id', getHabitById)     // GET /api/habits/123
[router.post](<http://router.post>)('/habits', createHabit)         // POST /api/habits
router.put('/habits/:id', updateHabit)      // PUT /api/habits/123
router.delete('/habits/:id', deleteHabit)   // DELETE /api/habits/123

HTTP Status Codes

Status codes communicate the result of an operation:

2xx Success

200 OK: Standard success
201 Created: New resource created
204 No Content: Success, no body

4xx Client Errors

400 Bad Request: Invalid input
401 Unauthorized: No auth
403 Forbidden: No permission
404 Not Found: Resource missing
409 Conflict: Duplicate resource

5xx Server Errors

500 Internal Error: Generic error
502 Bad Gateway: Upstream error
503 Service Unavailable: Temporary

Habit Controller Implementation

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File: src/controllers/habitController.ts

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