Idempotency of methods in Rest API - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the HTTP method that is idempotent.

Rest API

method = "[1]"  # This method should be idempotent

Drag options to blanks, or click blank then click option'

APOST

BCONNECT

CPUT

DTRACE

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing POST because it sends data, but POST is not idempotent.

Confusing CONNECT or TRACE as idempotent methods.

The PUT method is idempotent because calling it multiple times with the same data results in the same state.

2fill in blank

medium

Complete the code to specify the HTTP method that is NOT idempotent.

Rest API

method = "[1]"  # This method is generally NOT idempotent

Drag options to blanks, or click blank then click option'

AHEAD

BGET

CDELETE

DPOST

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing DELETE thinking it is not idempotent, but DELETE is idempotent.

Confusing GET as non-idempotent, but GET is idempotent.

The POST method is not idempotent because multiple identical requests can create multiple resources or have other side effects.

3fill in blank

hard

Fix the error in the code to correctly check if a method is idempotent.

Rest API

def is_idempotent(method):
    return method in [1]

Drag options to blanks, or click blank then click option'

A["POST", "PATCH"]

B["GET", "PUT", "DELETE", "HEAD", "OPTIONS", "TRACE"]

C["CONNECT", "POST"]

D["POST", "PUT"]

Attempts:

3 left

💡 Hint

Common Mistakes

Including POST or PATCH in the idempotent list.

Missing some idempotent methods like DELETE or HEAD.

The list in option D contains all standard HTTP methods that are idempotent.

4fill in blank

hard

Fill both blanks to create a dictionary mapping HTTP methods to their idempotency status.

Rest API

idempotency = {
    "GET": [1],
    "POST": [2]
}

Drag options to blanks, or click blank then click option'

ATrue

BFalse

C"Yes"

D"No"

Attempts:

3 left

💡 Hint

Common Mistakes

Using strings like "Yes" or "No" instead of boolean values.

Marking POST as idempotent.

GET is idempotent (True) and POST is not (False).

5fill in blank

hard

Fill all three blanks to complete the function that returns if a method is idempotent or not.

Rest API

def check_idempotency(method):
    idempotent_methods = [1]
    if method [2] idempotent_methods:
        return [3]
    else:
        return False

Drag options to blanks, or click blank then click option'

A["GET", "PUT", "DELETE", "HEAD", "OPTIONS", "TRACE"]

Bin

CTrue

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of 'in' for membership check.

Returning strings instead of boolean True.

The function checks if the method is in the list of idempotent methods and returns True if so.

Practice

1. Which HTTP method is idempotent, meaning it can be called multiple times without changing the result beyond the initial application?

easy

A. POST

B. CONNECT

C. PUT

D. PATCH

Solution

1. Step 1: Understand idempotency in HTTP methods

   Idempotent methods produce the same result no matter how many times they are called with the same input.

2. Step 2: Identify which methods are idempotent

   GET, PUT, and DELETE are idempotent. POST and PATCH are not because they can create or modify resources differently each time.

3. Final Answer:

   PUT -> Option C

4. Quick Check:

   PUT is idempotent = B [OK]

Hint: Remember: PUT replaces, POST creates new [OK]

Common Mistakes:

• Confusing POST as idempotent
• Thinking PATCH is idempotent
• Assuming CONNECT is idempotent

2. Which of the following is the correct syntax to perform an idempotent DELETE request using curl?

easy

A. curl -X DELETE https://api.example.com/resource/123

B. curl -X POST https://api.example.com/resource/123

C. curl -X PUT https://api.example.com/resource/123

D. curl -X GET https://api.example.com/resource/123

Solution

1. Step 1: Identify the HTTP method for deletion

   DELETE is the HTTP method used to remove a resource and is idempotent.

2. Step 2: Check curl syntax for DELETE

   The correct curl command uses -X DELETE followed by the resource URL.

3. Final Answer:

   curl -X DELETE https://api.example.com/resource/123 -> Option A

4. Quick Check:

   DELETE method syntax = C [OK]

Hint: DELETE uses -X DELETE in curl command [OK]

Common Mistakes:

• Using POST instead of DELETE
• Omitting -X flag for method
• Confusing GET with DELETE

3. Consider this sequence of HTTP requests to update a user's email:

PUT /users/42 {"email": "[e-mail]"}
PUT /users/42 {"email": "[e-mail]"}

What is the expected result after these two requests?

medium

A. User's email remains unchanged after the first update

B. User's email is updated once and remains the same after second request

C. User's email is updated twice, causing duplicate entries

D. An error occurs on the second request

Solution

1. Step 1: Understand PUT idempotency

   PUT replaces the resource with the given data. Multiple identical PUT requests do not change the resource after the first update.

2. Step 2: Analyze the two identical PUT requests

   The first request updates the email. The second request sends the same data, so no further change occurs.

3. Final Answer:

   User's email is updated once and remains the same after second request -> Option B

4. Quick Check:

   PUT idempotent means same result = A [OK]

Hint: PUT with same data does not change resource again [OK]

Common Mistakes:

• Assuming PUT creates duplicates
• Thinking second PUT causes error
• Confusing PUT with POST behavior

4. A developer wrote this code snippet to delete a resource:

fetch('https://api.example.com/items/10', { method: 'POST' })
  .then(response => console.log('Deleted'));

Why is this code incorrect for an idempotent delete operation?

medium

A. The response is not handled properly

B. The URL is missing a query parameter

C. The fetch method is missing headers

D. POST is not idempotent and should not be used for deletion

Solution

1. Step 1: Identify the HTTP method used

   The code uses POST to delete a resource, which is incorrect because POST is not idempotent.

2. Step 2: Understand correct method for deletion

   DELETE method should be used for idempotent deletion, ensuring repeated calls do not cause unintended effects.

3. Final Answer:

   POST is not idempotent and should not be used for deletion -> Option D

4. Quick Check:

   DELETE is idempotent, POST is not = A [OK]

Hint: Use DELETE, not POST, for idempotent deletes [OK]

Common Mistakes:

• Using POST for delete operations
• Ignoring HTTP method semantics
• Assuming POST is idempotent

5. You want to design an API endpoint to update user profile data safely. Which approach ensures idempotency and avoids duplicate updates if the client retries the request multiple times?

hard

A. Use PUT method to update the entire user profile with the same data each time

B. Use GET method with query parameters to update user data

C. Use PATCH method to partially update user data without tracking changes

D. Use POST method to update user data with a unique request ID

Solution

1. Step 1: Understand idempotent update methods

   PUT replaces the entire resource and is idempotent, so repeated calls with the same data do not cause duplicate changes.

2. Step 2: Evaluate options for safe updates

   POST is not idempotent, PATCH is not guaranteed idempotent, GET should not modify data. PUT is the best choice for safe, repeatable updates.

3. Final Answer:

   Use PUT method to update the entire user profile with the same data each time -> Option A

4. Quick Check:

   PUT ensures idempotent updates = D [OK]

Hint: PUT replaces resource fully, safe for retries [OK]

Common Mistakes:

• Using POST for updates expecting idempotency
• Assuming PATCH is always idempotent
• Trying to update data with GET