Self link for current resource in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this REST API self link generation code?

Given the following Python Flask code snippet that generates a self link for a resource, what is the output when accessing the endpoint /items/42?

Rest API

from flask import Flask, url_for, jsonify, request
app = Flask(__name__)

@app.route('/items/<int:item_id>')
def get_item(item_id):
    self_url = url_for('get_item', item_id=item_id, _external=True)
    return jsonify({'id': item_id, 'self': self_url})

with app.test_request_context():
    print(url_for('get_item', item_id=42, _external=True))

A "http://localhost/items/42"

B "/items/42"

C "http://localhost/items?id=42"

D "http://localhost/items/"

💡 Hint

Look at the _external=True parameter in url_for to understand the full URL generation.

The url_for function with _external=True generates the full URL including the scheme and host. The route uses a path parameter, so the URL includes /items/42.

🧠 Conceptual

intermediate

Which HTTP header is commonly used to indicate the self link of a resource in REST APIs?

In REST API design, which HTTP header is typically used to provide the URL of the current resource (self link) in the response headers?

A Content-Location

B Location

C Link

D Self

💡 Hint

Think about headers that can contain multiple URLs with relation types.

The Link header can include URLs with relation types such as rel="self" to indicate the self link of the resource.

🔧 Debug

advanced

Why does this code fail to generate a correct self link?

Consider this Node.js Express code snippet intended to add a self link to a JSON response. Why does it fail to produce the correct full URL for the self link?

Rest API

app.get('/users/:id', (req, res) => {
  const selfLink = `${req.protocol}://${req.hostname}/users/${req.params.id}`;
  res.json({ id: req.params.id, self: selfLink });
});

A req.protocol is undefined in Express, causing an error

B The template string syntax is incorrect

C req.params.id is not accessible in this route

D req.hostname does not include the port, so the URL may be incomplete

💡 Hint

Check how Express provides host and port information in requests.

req.hostname returns only the hostname without the port. If the server runs on a non-default port, the generated URL misses the port, making the self link incomplete.

📝 Syntax

advanced

Which option correctly adds a self link in a JSON response in Java Spring Boot?

Given a Spring Boot controller method, which code snippet correctly adds a self link to the returned resource using Spring HATEOAS?

Rest API

@GetMapping("/books/{id}")
public EntityModel<Book> getBook(@PathVariable Long id) {
    Book book = bookRepository.findById(id).orElseThrow();
    // Add self link here
}

A return EntityModel.of(book, linkTo(methodOn(BookController.class).getBook(id)).withSelfRel());

B return new EntityModel<>(book, new Link("/books/" + id));

C return ResponseEntity.ok(book).header("self", "/books/" + id).build();

D return book.add(linkTo(BookController.class).slash(id).withSelfRel());

💡 Hint

Look for the standard way to create self links with Spring HATEOAS using methodOn and linkTo.

Option A uses EntityModel.of with linkTo and methodOn to create a self link properly. Other options either misuse classes or headers.

🚀 Application

expert

How many items are in the resulting JSON when adding a self link to a nested resource?

Consider this JSON response for a REST API resource with a nested subresource and self links added at both levels: { "id": 10, "name": "Folder", "self": "http://api.example.com/folders/10", "files": [ { "id": 5, "filename": "doc.txt", "self": "http://api.example.com/folders/10/files/5" } ] } How many total keys are at the top level of the JSON object?

A 3

B 4

C 5

D 6

💡 Hint

Count the keys directly inside the outermost curly braces.

The top-level keys are: id, name, self, and files. That makes 4 keys total.

Practice

1. What is the main purpose of a self link in a REST API response?

easy

A. To provide the URL of the current resource for easy access

B. To link to a related but different resource

C. To show the API version used

D. To list all available endpoints in the API

Solution

1. Step 1: Understand the role of self link

   The self link points to the current resource's URL, allowing clients to access or refresh it easily.

2. Step 2: Differentiate from other links

   Other links may point to related resources or metadata, but self specifically means the current resource.

3. Final Answer:

   To provide the URL of the current resource for easy access -> Option A

4. Quick Check:

   Self link = current resource URL [OK]

Hint: Self link always points to the current resource URL [OK]

Common Mistakes:

• Confusing self link with related resource links
• Thinking self link shows API version
• Assuming self link lists all endpoints

2. Which of the following is the correct JSON structure to include a self link for a resource with URL https://api.example.com/items/42?

easy

A. {"links": {"self_link": "https://api.example.com/items/42"}}

B. {"_links": {"self": "https://api.example.com/items/42"}}

C. {"_links": {"current": "https://api.example.com/items/42"}}

D. {"self": "https://api.example.com/items/42"}

Solution

1. Step 1: Identify the standard key names

   The standard way is to use an object named _links containing a self key with the URL string.

2. Step 2: Compare options

   {"_links": {"self": "https://api.example.com/items/42"}} matches the standard exactly. Others use wrong keys or structure.

3. Final Answer:

   {"_links": {"self": "https://api.example.com/items/42"}} -> Option B

4. Quick Check:

   Use _links with self key for self link [OK]

Hint: Use _links object with self key for self link [OK]

Common Mistakes:

• Using 'links' instead of '_links'
• Using 'self_link' or 'current' instead of 'self'
• Placing self URL outside _links object

3. Given this API response snippet, what is the URL to access the current resource?

{
  "id": 10,
  "name": "Book",
  "_links": {
    "self": "https://api.example.com/products/10",
    "category": "https://api.example.com/categories/5"
  }
}

medium

A. https://api.example.com/products/10

B. https://api.example.com/products

C. https://api.example.com/categories/5

D. https://api.example.com/

Solution

1. Step 1: Locate the self link in the _links object

   The self link is under _links with key self, value is the current resource URL.

2. Step 2: Identify the URL value

   The value is "https://api.example.com/products/10", which is the URL for this product resource.

3. Final Answer:

   https://api.example.com/products/10 -> Option A

4. Quick Check:

   Self link URL = https://api.example.com/products/10 [OK]

Hint: Find _links.self for current resource URL [OK]

Common Mistakes:

• Choosing related links like category URL
• Picking base API URL instead of self
• Ignoring the _links object structure

4. You receive this JSON response but the self link is missing:

{
  "id": 5,
  "title": "Article",
  "_links": {
    "related": "https://api.example.com/articles/related"
  }
}

What is the best fix to add a self link for the current resource at https://api.example.com/articles/5?

medium

A. Add "self": "https://api.example.com/articles/5" at the root level

B. Add "self_link": "https://api.example.com/articles/5" inside the _links object

C. Add "self": "https://api.example.com/articles/5" inside the _links object

D. Add "link": "https://api.example.com/articles/5" inside the _links object

Solution

1. Step 1: Identify where self link belongs

   The self link must be inside the _links object with key exactly "self".

2. Step 2: Choose correct key and location

   Add "self": "https://api.example.com/articles/5" inside the _links object adds the correct key "self" with the URL inside _links. Other options use wrong keys or wrong placement.

3. Final Answer:

   Add "self": "https://api.example.com/articles/5" inside the _links object -> Option C

4. Quick Check:

   Self link key = "self" inside _links [OK]

Hint: Self link must be 'self' key inside _links object [OK]

Common Mistakes:

• Using wrong key names like self_link or link
• Placing self link outside _links object
• Omitting the self link entirely

5. You want to design a REST API response for a user resource with ID 7. Which JSON snippet correctly includes a self link and a related link to the user's orders at https://api.example.com/users/7/orders?

hard

A. {
"id": 7,
"name": "Alice",
"_links": {
"self": "https://api.example.com/users/7",
"related": "https://api.example.com/users/7/orders"
}
}

B. {
"id": 7,
"name": "Alice",
"links": {
"self": "https://api.example.com/users/7",
"orders": "https://api.example.com/users/7/orders"
}
}

C. {
"id": 7,
"name": "Alice",
"_links": {
"self_link": "https://api.example.com/users/7",
"orders_link": "https://api.example.com/users/7/orders"
}
}

D. {
"id": 7,
"name": "Alice",
"_links": {
"self": "https://api.example.com/users/7",
"orders": "https://api.example.com/users/7/orders"
}
}

Solution

1. Step 1: Confirm self link key and URL

   The self link must be under _links with key "self" and URL "https://api.example.com/users/7".

2. Step 2: Choose appropriate key for related orders link

   Using "orders" for the orders link is a standard practice to indicate the related resource. { "id": 7, "name": "Alice", "_links": { "self": "https://api.example.com/users/7", "orders": "https://api.example.com/users/7/orders" } } uses "orders" correctly.

3. Step 3: Check other options for correctness

   { "id": 7, "name": "Alice", "_links": { "self": "https://api.example.com/users/7", "orders": "https://api.example.com/users/7/orders" } } uses "orders" key which is standard. { "id": 7, "name": "Alice", "links": { "self": "https://api.example.com/users/7", "orders": "https://api.example.com/users/7/orders" } } uses "links" instead of "_links". { "id": 7, "name": "Alice", "_links": { "self_link": "https://api.example.com/users/7", "orders_link": "https://api.example.com/users/7/orders" } } uses non-standard keys "self_link" and "orders_link". The option with "related": "https://api.example.com/users/7/orders" uses a generic rel name which is less descriptive for the specific orders resource.

4. Final Answer:

   { "id": 7, "name": "Alice", "_links": { "self": "https://api.example.com/users/7", "orders": "https://api.example.com/users/7/orders" } } -> Option D

5. Quick Check:

   Use _links with self and orders keys for current and orders URLs [OK]

Hint: Use _links with self and orders keys for current and orders URLs [OK]

Common Mistakes:

• Using 'links' instead of '_links'
• Using non-standard keys like self_link
• Using generic 'related' instead of specific 'orders'