Action links for state transitions in Rest API - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an action link for the 'approve' transition.

Rest API

{
  "state": "pending",
  "actions": [
    {"name": "approve", "href": "/orders/[1]/approve"}
  ]
}

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

Aorder_id

Bid

C123

DorderId

Attempts:

3 left

💡 Hint

Common Mistakes

Using a literal number instead of a placeholder.

Using an underscore style that is inconsistent with the rest of the API.

The 'id' placeholder is commonly used to represent the resource identifier in REST API URLs.

2fill in blank

medium

Complete the code to add an action link for the 'cancel' transition with HTTP method DELETE.

Rest API

{
  "state": "approved",
  "actions": [
    {"name": "cancel", "href": "/orders/[1]/cancel", "method": "[2]"}
  ]
}

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

Aid

BorderId

CDELETE

DPOST

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'POST' instead of 'DELETE' for cancel action.

Using a wrong placeholder for the resource id.

The 'id' is the resource identifier and 'DELETE' is the HTTP method used to cancel or remove a resource.

3fill in blank

hard

Fix the error in the action link for the 'ship' transition by completing the HTTP method.

Rest API

{
  "state": "paid",
  "actions": [
    {"name": "ship", "href": "/orders/[1]/ship", "method": "[2]"}
  ]
}

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

Aid

BPUT

CGET

DPATCH

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'GET' which is for retrieving data, not updating.

Using 'PATCH' which is for partial updates but 'ship' implies a full state change.

The 'ship' action updates the order state, so 'PUT' is the appropriate HTTP method to update the resource.

4fill in blank

hard

Fill both blanks to add action links for 'approve' and 'reject' transitions with correct HTTP methods.

Rest API

{
  "state": "pending",
  "actions": [
    {"name": "approve", "href": "/orders/[1]/approve", "method": "[2]"},
    {"name": "reject", "href": "/orders/[1]/reject", "method": "[2]"}
  ]
}

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

Aid

BPOST

CPUT

DDELETE

Attempts:

3 left

💡 Hint

Common Mistakes

Using different identifiers for the two actions.

Using 'PUT' or 'DELETE' instead of 'POST' for these transitions.

Both 'approve' and 'reject' are state transitions that create a new state, so 'POST' is the correct HTTP method and 'id' is the resource identifier.

5fill in blank

hard

Fill all three blanks to create an action link for 'refund' with resource id, HTTP method, and content type.

Rest API

{
  "state": "shipped",
  "actions": [
    {
      "name": "refund",
      "href": "/orders/[1]/refund",
      "method": "[2]",
      "headers": {"Content-Type": "[3]"}
    }
  ]
}

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

Aid

BPOST

Capplication/json

DPUT

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'PUT' instead of 'POST' for refund.

Omitting the content type or using an incorrect one.

The 'refund' action uses the resource 'id', the 'POST' method to submit the refund request, and the content type 'application/json' for the request body.

Practice

1. What is the main purpose of action links in REST APIs for state transitions?

easy

A. To format the API response as JSON

B. To store data permanently on the server

C. To authenticate users before accessing the API

D. To provide URLs that clients can use to change the current state

Solution

1. Step 1: Understand what action links represent

   Action links are URLs included in API responses that show possible next steps or actions a client can take to change the state.

2. Step 2: Identify the purpose of action links

   They guide clients on how to move from one state to another by calling these URLs.

3. Final Answer:

   To provide URLs that clients can use to change the current state -> Option D

4. Quick Check:

   Action links = URLs for state change [OK]

Hint: Action links = URLs for next steps in state [OK]

Common Mistakes:

• Confusing action links with authentication tokens
• Thinking action links store data
• Assuming action links format data

2. Which of the following is the correct way to include an action link for a "cancel" operation in a REST API JSON response?

easy

A. "cancel": "POST https://api.example.com/orders/123/cancel"

B. "actions": {"cancel": "https://api.example.com/orders/123/cancel"}

C. "cancel_url": "https://api.example.com/orders/123/cancel"

D. "cancel_link": "GET https://api.example.com/orders/123/cancel"

Solution

1. Step 1: Recognize common pattern for action links

   Action links are often grouped under an "actions" key with action names as keys and URLs as values.

2. Step 2: Check each option's format

   "actions": {"cancel": "https://api.example.com/orders/123/cancel"} correctly uses an "actions" object with "cancel" as key and the URL as value, which is a clear and common pattern.

3. Final Answer:

   "actions": {"cancel": "https://api.example.com/orders/123/cancel"} -> Option B

4. Quick Check:

   Action links grouped under "actions" = "actions": {"cancel": "https://api.example.com/orders/123/cancel"} [OK]

Hint: Group action links under "actions" key for clarity [OK]

Common Mistakes:

• Using HTTP method inside the URL string
• Not grouping actions under a common key
• Using incorrect HTTP method for cancel

3. Given this JSON response snippet from a REST API:

{
  "state": "pending",
  "actions": {
    "approve": "https://api.example.com/items/42/approve",
    "reject": "https://api.example.com/items/42/reject"
  }
}

What will happen if the client calls the URL in the "approve" action link?

medium

A. The item state will change to approved

B. The item will be deleted

C. The client will receive an error because the URL is invalid

D. The item state will remain pending

Solution

1. Step 1: Understand the meaning of the "approve" action link

   The "approve" link is provided as a next step to change the state from "pending" to "approved" by calling that URL.

2. Step 2: Predict the effect of calling the approve URL

   Calling the approve URL triggers the state transition to "approved" as intended by the API design.

3. Final Answer:

   The item state will change to approved -> Option A

4. Quick Check:

   Calling "approve" URL = state changes to approved [OK]

Hint: Action link name hints the state change [OK]

Common Mistakes:

• Assuming the URL deletes the item
• Thinking the URL is invalid
• Believing state stays the same after action

4. A REST API response includes this action link:

"actions": {"complete": "https://api.example.com/tasks/99/complete"}

But calling this URL returns a 405 Method Not Allowed error. What is the most likely cause?

medium

A. The task with ID 99 does not exist

B. The URL is misspelled in the response

C. The client used GET instead of POST to call the action link

D. The server is down

Solution

1. Step 1: Understand 405 Method Not Allowed error

   This error means the HTTP method used is not supported by the URL endpoint.

2. Step 2: Identify common cause with action links

   Action links for state changes usually require POST, but clients often call them with GET by mistake.

3. Final Answer:

   The client used GET instead of POST to call the action link -> Option C

4. Quick Check:

   405 error = wrong HTTP method used [OK]

Hint: Use POST for action links, not GET [OK]

Common Mistakes:

• Assuming URL is misspelled without checking
• Thinking 405 means resource missing
• Blaming server downtime without evidence

5. You want to design a REST API for an order system with states: new, paid, shipped, and cancelled. Which of the following JSON responses best uses action links to guide clients through valid state transitions when the order is in paid state?

hard

A. {
"state": "paid",
"actions": {
"ship": "https://api.example.com/orders/555/ship",
"cancel": "https://api.example.com/orders/555/cancel"
}
}

B. {
"state": "paid",
"actions": {
"pay": "https://api.example.com/orders/555/pay",
"cancel": "https://api.example.com/orders/555/cancel"
}
}

C. {
"state": "paid",
"actions": {
"new": "https://api.example.com/orders/555/new",
"cancel": "https://api.example.com/orders/555/cancel"
}
}

D. {
"state": "paid",
"actions": {
"ship": "https://api.example.com/orders/555/ship",
"pay": "https://api.example.com/orders/555/pay"
}
}

Solution

1. Step 1: Identify valid next states from "paid"

   From "paid", the order can be "shipped" or "cancelled" but not "pay" or "new" again.

2. Step 2: Check which options provide correct action links

   { "state": "paid", "actions": { "ship": "https://api.example.com/orders/555/ship", "cancel": "https://api.example.com/orders/555/cancel" } } correctly offers "ship" and "cancel" actions, matching valid transitions.

3. Final Answer:

   JSON with "ship" and "cancel" actions for "paid" state -> Option A

4. Quick Check:

   Valid next actions for "paid" = ship, cancel [OK]

Hint: Only include valid next states as action links [OK]

Common Mistakes:

• Including actions that repeat previous states
• Missing valid next state actions
• Confusing state names with action names