CRUD Operations: Mapping HTTP Methods to Data Operations

CRUD — Create, Read, Update, Delete — is the foundation of every data-driven application. REST maps these four operations to HTTP methods in a clean, consistent pattern. In this lesson, we will walk through the complete CRUD lifecycle with detailed examples you can run against live APIs.

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1. The CRUD Lifecycle

Every resource in a REST API goes through a lifecycle:

graph LR
    A["CREATE<br/>POST /items"] --> B["READ<br/>GET /items/1"]
    B --> C["UPDATE<br/>PUT or PATCH /items/1"]
    C --> D["DELETE<br/>DELETE /items/1"]
    D --> E["Gone<br/>404 on GET /items/1"]

    style A fill:#059669,color:#fff
    style B fill:#0891b2,color:#fff
    style C fill:#d97706,color:#fff
    style D fill:#dc2626,color:#fff
    style E fill:#6b7280,color:#fff

The Complete Mapping

CRUD	HTTP Method	URL Pattern	Request Body	Response Code
Create	POST	/resources	New resource data	201 Created
Read All	GET	/resources	None	200 OK
Read One	GET	/resources/:id	None	200 OK
Full Update	PUT	/resources/:id	Complete resource	200 OK
Partial Update	PATCH	/resources/:id	Changed fields only	200 OK
Delete	DELETE	/resources/:id	None	204 No Content

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2. Create (POST)

When to Use POST

• Adding a new user to the system
• Creating a blog post
• Placing an order
• Submitting a form

Complete Example

curl -X POST https://jsonplaceholder.typicode.com/posts \
  -H "Content-Type: application/json" \
  -d '{
    "title": "Understanding CRUD",
    "body": "CRUD maps perfectly to HTTP methods in REST.",
    "userId": 1
  }'

Response (201 Created):

{
  "title": "Understanding CRUD",
  "body": "CRUD maps perfectly to HTTP methods in REST.",
  "userId": 1,
  "id": 101
}

What the Server Does

1. Validates the input data
2. Generates a unique ID
3. Sets default values (timestamps, status)
4. Inserts into the database
5. Returns the complete resource with its new ID

POST Best Practices

Practice	Description
Return the created resource	Include it in the response body
Return 201 Created	Not 200 OK
Include Location header	URL of the new resource
Validate input	Return 400 for invalid data
Set defaults server-side	Timestamps, status, generated fields

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3. Read (GET)

Reading Collections

# All posts
curl https://jsonplaceholder.typicode.com/posts

# Filtered posts (by user)
curl "https://jsonplaceholder.typicode.com/posts?userId=1"

Collection responses return an array:

[
  {"id": 1, "title": "First Post", "userId": 1},
  {"id": 2, "title": "Second Post", "userId": 1},
  ...
]

Reading Individual Resources

curl https://jsonplaceholder.typicode.com/posts/1

Individual responses return a single object:

{
  "userId": 1,
  "id": 1,
  "title": "sunt aut facere...",
  "body": "quia et suscipit..."
}

Reading Related Resources

# Comments on post 1
curl https://jsonplaceholder.typicode.com/posts/1/comments

# Todos for user 3
curl https://jsonplaceholder.typicode.com/users/3/todos

Advanced Reading Patterns

# Pagination
curl "https://api.example.com/products?page=2&limit=10"

# Sorting
curl "https://api.example.com/products?sort=price&order=asc"

# Searching
curl "https://api.example.com/products?q=laptop"

# Multiple filters
curl "https://api.example.com/products?category=electronics&inStock=true&maxPrice=500"

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4. Update (PUT and PATCH)

Full Update with PUT

PUT replaces the entire resource:

curl -X PUT https://jsonplaceholder.typicode.com/posts/1 \
  -H "Content-Type: application/json" \
  -d '{
    "id": 1,
    "title": "Completely New Title",
    "body": "Completely new body content replacing everything.",
    "userId": 1
  }'

Partial Update with PATCH

PATCH changes only specified fields:

curl -X PATCH https://jsonplaceholder.typicode.com/posts/1 \
  -H "Content-Type: application/json" \
  -d '{"title": "Only Title Changed"}'

Side-by-Side Comparison

graph TD
    subgraph "Original Resource"
        O["id: 1<br/>title: 'Hello'<br/>body: 'World'<br/>status: 'draft'"]
    end

    subgraph "After PUT {title:'New'}"
        P["id: 1<br/>title: 'New'<br/>body: null<br/>status: null"]
    end

    subgraph "After PATCH {title:'New'}"
        Q["id: 1<br/>title: 'New'<br/>body: 'World'<br/>status: 'draft'"]
    end

    O --> P
    O --> Q

    style O fill:#4f46e5,color:#fff
    style P fill:#d97706,color:#fff
    style Q fill:#059669,color:#fff

PUT with only title might set body and status to null (they were not included). PATCH with only title leaves body and status untouched.

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5. Delete (DELETE)

curl -X DELETE https://jsonplaceholder.typicode.com/posts/1

Delete Response Patterns

Pattern	Status	Body
No content	204 No Content	Empty
Confirmation	200 OK	{"deleted": true}
Return deleted resource	200 OK	The deleted resource data

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6. Complete CRUD Workflow

Let us perform a complete lifecycle on a single resource:

# 1. CREATE a post
curl -X POST https://jsonplaceholder.typicode.com/posts \
  -H "Content-Type: application/json" \
  -d '{"title":"My Post","body":"Original content","userId":1}'
# Response: 201 Created, id: 101

# 2. READ the post
curl https://jsonplaceholder.typicode.com/posts/101
# Response: 200 OK

# 3. UPDATE the post (partial)
curl -X PATCH https://jsonplaceholder.typicode.com/posts/101 \
  -H "Content-Type: application/json" \
  -d '{"title":"Updated Post"}'
# Response: 200 OK

# 4. DELETE the post
curl -X DELETE https://jsonplaceholder.typicode.com/posts/101
# Response: 200 OK

# 5. TRY TO READ (should fail)
curl https://jsonplaceholder.typicode.com/posts/101
# Response: 404 Not Found (in a real API)

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7. Error Handling in CRUD

Each CRUD operation has common errors:

Operation	Error	Status	Cause
Create	Missing required field	400	Body missing data
Create	Duplicate entry	409	Resource already exists
Read	Resource not found	404	Wrong ID or deleted
Update	Resource not found	404	Wrong ID
Update	Invalid data	422	Bad field values
Delete	Resource not found	404	Already deleted
Any	Not authenticated	401	Missing token
Any	Not authorized	403	Insufficient role

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Summary and Key Takeaways

1. CRUD maps to HTTP: Create=POST, Read=GET, Update=PUT/PATCH, Delete=DELETE.
2. POST creates and returns 201; GET reads and returns 200.
3. PUT replaces entirely; PATCH updates only specified fields.
4. DELETE removes resources and returns 204 (no content) or 200.
5. Every CRUD operation has expected error responses you should handle.
6. A complete resource lifecycle goes: Create → Read → Update → Delete.

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