Link relations in responses in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this REST API response with link relations?

Given the following JSON response from a REST API, what is the value of the "next" link relation URL?

Rest API

{
  "data": ["item1", "item2"],
  "links": {
    "self": "https://api.example.com/items?page=1",
    "next": "https://api.example.com/items?page=2",
    "prev": null
  }
}

A "https://api.example.com/items?page=2"

B "https://api.example.com/items?page=1"

C null

D "https://api.example.com/items?page=3"

💡 Hint

Look for the "next" key inside the "links" object.

The "next" link relation provides the URL for the next page of items, which is "https://api.example.com/items?page=2".

🧠 Conceptual

intermediate

What is the purpose of link relations in REST API responses?

Why do REST APIs include link relations like "self", "next", and "prev" in their responses?

A To provide URLs that describe how to navigate or interact with related resources.

B To store user credentials for authentication.

C To compress the response data for faster transfer.

D To define the data schema of the response.

💡 Hint

Think about how clients can use these links to move between pages or related data.

Link relations help clients discover related resources or actions by providing URLs with semantic names like "next" or "self".

🔧 Debug

advanced

Why does this REST API response cause a client error when following the "next" link?

Consider this JSON response snippet: { "links": { "self": "https://api.example.com/items?page=1", "next": "htp://api.example.com/items?page=2" } } Why will a client fail to fetch the "next" page?

A The "self" link is missing a trailing slash.

B The "next" URL has a typo in the scheme: "htp" instead of "http".

C The "next" link is missing the query parameter "page".

D The JSON response is missing a "prev" link.

💡 Hint

Check the URL scheme spelling carefully.

The "next" link URL uses "htp" which is not a valid scheme, causing clients to fail when trying to fetch it.

📝 Syntax

advanced

Which option correctly represents a HAL-style link relation in JSON?

HAL (Hypertext Application Language) uses a specific JSON format for links. Which of the following is the correct HAL link representation for a "self" link?

A "links": { "self": "https://api.example.com/items/1" }

B "links": { "self": { "url": "https://api.example.com/items/1" } }

C "_links": { "self": "https://api.example.com/items/1" }

D "_links": { "self": { "href": "https://api.example.com/items/1" } }

💡 Hint

HAL requires the "href" key inside the link object.

HAL defines links inside an "_links" object with each link as an object containing an "href" property.

🚀 Application

expert

How many link relations are present in this paginated API response?

Given this JSON response: { "data": ["a", "b"], "links": { "self": "https://api.example.com/data?page=3", "first": "https://api.example.com/data?page=1", "prev": "https://api.example.com/data?page=2", "next": "https://api.example.com/data?page=4", "last": "https://api.example.com/data?page=10" } } How many distinct link relations are included in the "links" object?

A 3

B 4

C 5

D 6

💡 Hint

Count all keys inside the "links" object.

The "links" object contains "self", "first", "prev", "next", and "last" — a total of 5 link relations.

Practice

1. What is the main purpose of using link relations in REST API responses?

easy

A. To define the HTTP methods allowed on a resource

B. To encrypt the data sent between client and server

C. To specify the data format like JSON or XML

D. To describe how different resources are connected and provide URLs for related actions

Solution

1. Step 1: Understand link relations concept

   Link relations describe the relationship between resources and provide URLs to related resources or actions.

2. Step 2: Identify the purpose in REST API responses

   They help clients navigate the API by following links instead of hardcoding URLs.

3. Final Answer:

   To describe how different resources are connected and provide URLs for related actions -> Option D

4. Quick Check:

   Link relations = resource connections and URLs [OK]

Hint: Link relations connect resources with URLs in responses [OK]

Common Mistakes:

• Confusing link relations with data encryption
• Thinking link relations define data format
• Mixing link relations with HTTP method definitions

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

easy

A. "_links": { "self": { "href": "/users/123" } }

B. "links": [ { "url": "/users/123" } ]

C. "link": "/users/123"

D. "href": { "self": "/users/123" }

Solution

1. Step 1: Recall standard link relation format in JSON

   Standard uses a _links object with named relations like self containing an href URL.

2. Step 2: Match the correct JSON structure

   "_links": { "self": { "href": "/users/123" } } matches this format exactly, others do not follow the standard naming or structure.

3. Final Answer:

   "_links": { "self": { "href": "/users/123" } } -> Option A

4. Quick Check:

   Standard link relation = _links with self and href [OK]

Hint: Look for _links with self and href keys [OK]

Common Mistakes:

• Using 'links' instead of '_links'
• Missing 'href' inside the relation object
• Using arrays instead of objects for link relations

3. Given this JSON response snippet:

{
  "_links": {
    "self": { "href": "/orders/42" },
    "cancel": { "href": "/orders/42/cancel" }
  }
}

What URL should a client use to cancel order 42?

medium

A. /orders/42

B. /orders/cancel/42

C. /orders/42/cancel

D. /orders/42/cancelled

Solution

1. Step 1: Locate the 'cancel' link relation in the JSON

   The 'cancel' relation has the href value "/orders/42/cancel" which is the URL to cancel the order.

2. Step 2: Confirm the correct URL for cancellation

   The client should use the URL exactly as given in the 'cancel' href to perform the cancel action.

3. Final Answer:

   /orders/42/cancel -> Option C

4. Quick Check:

   Cancel URL = /orders/42/cancel [OK]

Hint: Use the href under the 'cancel' link relation [OK]

Common Mistakes:

• Using the 'self' URL instead of 'cancel'
• Rearranging URL parts incorrectly
• Guessing URL instead of reading from response

4. You receive this partial JSON response:

{
  "_links": {
    "self": { "href": "/products/7" },
    "edit": { "url": "/products/7/edit" }
  }
}

What is wrong with the link relations in this response?

medium

A. The 'edit' relation uses 'url' instead of 'href'

B. The 'self' relation should not be included

C. The 'href' value for 'self' is missing a domain

D. The '_links' key should be named 'links'

Solution

1. Step 1: Check the property names inside link relations

   Standard link relations use 'href' to specify the URL, not 'url'.

2. Step 2: Identify the incorrect property

   The 'edit' relation incorrectly uses 'url' instead of 'href'.

3. Final Answer:

   The 'edit' relation uses 'url' instead of 'href' -> Option A

4. Quick Check:

   Link relation URLs must use 'href' key [OK]

Hint: Link URLs always use 'href', not 'url' [OK]

Common Mistakes:

• Thinking 'url' is acceptable instead of 'href'
• Expecting full domain in href for relative URLs
• Renaming '_links' to 'links' incorrectly

5. You want to design a REST API response for a blog post that includes links to the post itself, the author's profile, and comments. Which JSON structure correctly uses link relations to represent these?

hard

A. { "links": [ { "rel": "self", "url": "/posts/10" }, { "rel": "author", "url": "/users/5" }, { "rel": "comments", "url": "/posts/10/comments" } ] }

B. { "_links": { "self": { "href": "/posts/10" }, "author": { "href": "/users/5" }, "comments": { "href": "/posts/10/comments" } } }

C. { "_links": { "self": "/posts/10", "author": "/users/5", "comments": "/posts/10/comments" } }

D. { "_links": { "self": { "url": "/posts/10" }, "author": { "url": "/users/5" }, "comments": { "url": "/posts/10/comments" } } }

Solution

1. Step 1: Recall the correct link relation format

   Each link relation should be an object with an 'href' key inside the '_links' object.

2. Step 2: Evaluate each option's structure

   { "_links": { "self": { "href": "/posts/10" }, "author": { "href": "/users/5" }, "comments": { "href": "/posts/10/comments" } } } correctly uses '_links' with 'self', 'author', and 'comments' keys, each having an 'href' URL. Options B and D use 'url' instead of 'href', and C uses strings instead of objects.

3. Final Answer:

   { "_links": { "self": { "href": "/posts/10" }, "author": { "href": "/users/5" }, "comments": { "href": "/posts/10/comments" } } } -> Option B

4. Quick Check:

   Use '_links' with objects containing 'href' URLs [OK]

Hint: Use '_links' with 'href' keys for each relation [OK]

Common Mistakes:

• Using 'url' instead of 'href' for links
• Using arrays instead of objects for link relations
• Assigning string URLs directly without 'href' objects