POST for creating resources in Rest API

Introduction

POST is used to send data to a server to create a new item or resource. It helps add new things like users, posts, or products.

When you want to add a new user to a website.

When you need to upload a new photo or file.

When creating a new blog post or article.

When submitting a form with information to save.

When adding a new product to an online store.

Syntax

Rest API

POST /resource HTTP/1.1
Host: example.com
Content-Type: application/json

{
  "key": "value"
}

The POST request sends data in the body, usually in JSON format.

The URL points to the collection where the new resource will be added.

Examples

This creates a new user with name and email.

Rest API

POST /users HTTP/1.1
Host: example.com
Content-Type: application/json

{
  "name": "Alice",
  "email": "[e-mail]"
}

This adds a new blog post with a title and content.

Rest API

POST /posts HTTP/1.1
Host: example.com
Content-Type: application/json

{
  "title": "My First Post",
  "content": "Hello world!"
}

Sample Program

This Python program sends a POST request to create a new post with title, body, and userId. It prints the status code and the response from the server.

Rest API

import requests

url = 'https://jsonplaceholder.typicode.com/posts'
data = {
    'title': 'foo',
    'body': 'bar',
    'userId': 1
}

response = requests.post(url, json=data)
print('Status code:', response.status_code)
print('Response body:', response.json())

Important Notes

POST requests usually return status code 201 when a resource is created successfully.

The server response often includes the new resource's ID or details.

Always set the Content-Type header to tell the server the data format.

Summary

POST is used to create new resources by sending data to the server.

Data is sent in the request body, often as JSON.

Successful creation usually returns status 201 and the new resource info.

Practice

1. What is the primary purpose of the POST method in REST APIs?

easy

A. To create a new resource on the server

B. To retrieve data from the server

C. To update an existing resource completely

D. To delete a resource from the server

Solution

1. Step 1: Understand HTTP methods

   HTTP methods have specific roles: GET retrieves, POST creates, PUT updates, DELETE removes.

2. Step 2: Identify POST's role

   POST sends data to the server to create a new resource, unlike GET which only fetches data.

3. Final Answer:

   To create a new resource on the server -> Option A

4. Quick Check:

   POST = Create resource [OK]

Hint: POST is for sending data to create something new [OK]

Common Mistakes:

• Confusing POST with GET which only fetches data
• Thinking POST updates existing resources fully
• Assuming POST deletes resources

2. Which of the following is the correct way to send data in a POST request to create a resource?

easy

A. Include data in the URL query parameters

B. Send data in the request body as JSON

C. Send data as HTTP headers

D. Send data as a cookie

Solution

1. Step 1: Identify where POST data goes

   POST requests send data in the request body, not in URL or headers.

2. Step 2: Recognize common data format

   JSON is the standard format for sending structured data in the body for REST APIs.

3. Final Answer:

   Send data in the request body as JSON -> Option B

4. Quick Check:

   POST data = request body JSON [OK]

Hint: POST data goes in the body, not URL or headers [OK]

Common Mistakes:

• Putting data in URL query instead of body
• Trying to send data via headers
• Using cookies to send creation data

3. Given this Python code using the requests library, what will be the HTTP status code if the resource is created successfully?

import requests
url = 'https://api.example.com/items'
data = {'name': 'Book', 'price': 12.99}
response = requests.post(url, json=data)
print(response.status_code)

medium

A. 200

B. 404

C. 201

D. 500

Solution

1. Step 1: Understand POST success codes

   When a resource is created, the server usually returns HTTP status 201 Created.

2. Step 2: Analyze the code behavior

   The code sends a POST request with JSON data; if successful, response.status_code will be 201.

3. Final Answer:

   201 -> Option C

4. Quick Check:

   POST success = 201 Created [OK]

Hint: 201 means resource created successfully [OK]

Common Mistakes:

• Confusing 200 OK with 201 Created
• Assuming 404 means success
• Thinking 500 means success

4. You wrote this POST request code but get a 400 Bad Request error. What is the likely problem?

import requests
url = 'https://api.example.com/users'
data = {'username': 'alice'}
response = requests.post(url, data=data)
print(response.status_code)

medium

A. The data should be sent as JSON, not form data

B. The URL is incorrect for POST requests

C. POST requests cannot send data

D. The server does not support HTTPS

Solution

1. Step 1: Check data sending method

   Using data=data sends form-encoded data, but API expects JSON for POST creation.

2. Step 2: Fix data format

   Use json=data in requests.post to send JSON body, which the server accepts.

3. Final Answer:

   The data should be sent as JSON, not form data -> Option A

4. Quick Check:

   Send JSON with json= parameter [OK]

Hint: Use json= not data= to send JSON body [OK]

Common Mistakes:

• Sending form data instead of JSON
• Assuming URL is wrong without checking
• Thinking POST can't send data
• Ignoring HTTPS requirement

5. You want to create a new blog post resource with title and content using a POST request. Which of these JSON payloads correctly represents the data to send in the request body?

hard

A. ["title", "My Day", "content", "It was sunny."]

B. "title=My Day&content=It was sunny."

C. {"My Day": "title", "It was sunny.": "content"}

D. {"title": "My Day", "content": "It was sunny."}

Solution

1. Step 1: Understand JSON object structure

   JSON objects use key-value pairs with keys as strings and values as data.

2. Step 2: Identify correct JSON format

   {"title": "My Day", "content": "It was sunny."} correctly uses keys "title" and "content" with their string values in an object.

3. Final Answer:

   {"title": "My Day", "content": "It was sunny."} -> Option D

4. Quick Check:

   JSON object with keys and values = {"title": "My Day", "content": "It was sunny."} [OK]

Hint: JSON data must be key-value pairs inside braces {} [OK]

Common Mistakes:

• Using JSON arrays instead of objects
• Swapping keys and values
• Sending URL-encoded string instead of JSON