Related resource links in Rest API - Time & Space Complexity

Time Complexity: Related resource links

O(n)

Understanding Time Complexity

When a REST API returns related resource links, it often loops through data to build these links.

We want to know how the time to create these links grows as the number of resources increases.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

GET /users/{id}/related

// Pseudocode
related_resources = []
for friend in user.friends:
    related_resources.append({"link": f"/users/{friend.id}"})
return related_resources

This code builds a list of links to related user resources (friends) for a given user.

Identify Repeating Operations

• Primary operation: Looping through each friend in the user's friends list.
• How many times: Once for every friend the user has.

How Execution Grows With Input

As the number of friends grows, the time to build links grows too.

Input Size (n)	Approx. Operations
10	About 10 link creations
100	About 100 link creations
1000	About 1000 link creations

Pattern observation: The work grows directly with the number of friends.

Final Time Complexity

Time Complexity: O(n)

This means the time to build related links grows in a straight line with the number of related resources.

Common Mistake

[X] Wrong: "Building related links takes the same time no matter how many friends there are."

[OK] Correct: Each friend adds one link, so more friends mean more work and more time.

Interview Connect

Understanding how loops over related resources affect time helps you explain API performance clearly and confidently.

Self-Check

"What if we also fetched each friend's recent posts inside the loop? How would the time complexity change?"

Practice

1. What is the main purpose of related resource links in a REST API?

easy

A. To store user credentials securely

B. To speed up the server response time

C. To connect related data so users can easily navigate between resources

D. To encrypt data sent over the network

Solution

1. Step 1: Understand the role of related resource links

   Related resource links provide connections between different pieces of data in an API, making it easier to find connected information.

2. Step 2: Identify the correct purpose

   Among the options, only connecting related data for easy navigation matches the purpose of related resource links.

3. Final Answer:

   To connect related data so users can easily navigate between resources -> Option C

4. Quick Check:

   Related resource links = connect data [OK]

Hint: Related links help users jump between connected data [OK]

Common Mistakes:

• Confusing related links with security features
• Thinking related links speed up server
• Assuming related links encrypt data

2. Which of the following is the correct way to include a related resource link in a JSON REST API response?

easy

A. "related": "https://api.example.com/users/123/orders"

B. "related": users/123/orders

C. "related":

D. "related": {url: "https://api.example.com/users/123/orders"}

Solution

1. Step 1: Check JSON syntax for URLs

   In JSON, URLs should be strings enclosed in double quotes without angle brackets or unquoted text.

2. Step 2: Identify the correct format

   "related": "https://api.example.com/users/123/orders" correctly uses a string with the full URL in quotes. Options B and C are invalid JSON strings, and D uses an object instead of a string.

3. Final Answer:

   "related": "https://api.example.com/users/123/orders" -> Option A

4. Quick Check:

   Related link URL must be a quoted string [OK]

Hint: URLs in JSON must be quoted strings without brackets [OK]

Common Mistakes:

• Leaving URLs unquoted
• Using angle brackets around URLs
• Using objects instead of strings for links

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

{
  "id": 10,
  "name": "Book",
  "related": "https://api.example.com/books/10/author"
}

What does the related link represent?

medium

A. The URL to list all books

B. The URL to update the book information

C. The URL to delete the book

D. The URL to fetch the author details of the book

Solution

1. Step 1: Analyze the related link URL

   The URL ends with "/books/10/author", which suggests it points to the author of book with ID 10.

2. Step 2: Match URL purpose with options

   Only The URL to fetch the author details of the book correctly describes this as fetching author details. Other options refer to book update, delete, or list, which do not match the URL.

3. Final Answer:

   The URL to fetch the author details of the book -> Option D

4. Quick Check:

   Related link points to connected resource = author [OK]

Hint: Look at URL path to identify related resource type [OK]

Common Mistakes:

• Assuming related link is for update or delete
• Confusing related link with main resource URL
• Ignoring the path after resource ID

4. You have this REST API response snippet:

{
  "id": 5,
  "name": "Alice",
  "related": "api.example.com/users/5/friends"
}

Why might this related link cause problems for clients?

medium

A. The related link points to a wrong resource

B. The URL is missing the protocol (http:// or https://)

C. The JSON format is invalid

D. The related link is too long

Solution

1. Step 1: Check the related link format

   The link "api.example.com/users/5/friends" lacks the protocol prefix like "https://" which is required for clients to resolve the full URL.

2. Step 2: Identify the impact

   Without the protocol, clients may fail to fetch the related resource or assume a wrong protocol, causing errors.

3. Final Answer:

   The URL is missing the protocol (http:// or https://) -> Option B

4. Quick Check:

   Related links need full URLs with protocol [OK]

Hint: Always include http:// or https:// in related links [OK]

Common Mistakes:

• Ignoring missing protocol in URLs
• Thinking JSON is invalid due to link format
• Assuming link length causes issues

5. You want to design a REST API response for a blog post that includes related links to the author and comments. Which JSON structure correctly shows these related resource links?

hard

A. {
"id": 101,
"title": "REST APIs",
"related": {
"author": "https://api.example.com/users/42",
"comments": "https://api.example.com/posts/101/comments"
}
}

B. {
"id": 101,
"title": "REST APIs",
"related": [
"https://api.example.com/users/42",
"https://api.example.com/posts/101/comments"
]
}

C. {
"id": 101,
"title": "REST APIs",
"related": "https://api.example.com/users/42, https://api.example.com/posts/101/comments"
}

D. {
"id": 101,
"title": "REST APIs",
"related": null
}

Solution

1. Step 1: Understand how to represent multiple related links

   When multiple related resources exist, it's best to use an object with named keys for clarity, not a list or comma-separated string.

2. Step 2: Evaluate each option

   { "id": 101, "title": "REST APIs", "related": { "author": "https://api.example.com/users/42", "comments": "https://api.example.com/posts/101/comments" } } uses an object with keys "author" and "comments" pointing to URLs, which is clear and correct. { "id": 101, "title": "REST APIs", "related": [ "https://api.example.com/users/42", "https://api.example.com/posts/101/comments" ] } uses a list without labels, making it unclear. { "id": 101, "title": "REST APIs", "related": "https://api.example.com/users/42, https://api.example.com/posts/101/comments" } uses a string with comma-separated URLs, which is not standard. { "id": 101, "title": "REST APIs", "related": null } has null, which provides no links.

3. Final Answer:

   Use an object with named related links for clarity -> Option A

4. Quick Check:

   Multiple related links = object with named URLs [OK]

Hint: Use named keys for multiple related links in JSON [OK]

Common Mistakes:

• Using arrays without labels for related links
• Combining URLs in one string
• Leaving related links empty or null