HAL format overview in Rest API - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the main HAL JSON object with a _links section.

Rest API

{
  "_links": [1]
}

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

A"self": "/orders"

B["self", "/orders"]

C[{"href": "/orders"}]

D{"self": {"href": "/orders"}}

Attempts:

3 left

💡 Hint

Common Mistakes

Using an array instead of an object for _links

Missing the href key inside the link object

The _links section in HAL is a JSON object mapping relation names to link objects. The correct format is an object with a self key containing an href key.

2fill in blank

medium

Complete the code to add an embedded resource named 'orders' with an empty array.

Rest API

{
  "_embedded": {
    "[1]": []
  }
}

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

Aorders

Bitems

Clinks

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using reserved keys like 'self' or 'links' as embedded resource names

Using singular instead of plural resource names

In HAL, embedded resources are grouped under _embedded. The key is the resource name, here orders.

3fill in blank

hard

Fix the error in the HAL link object by completing the href value correctly.

Rest API

{
  "_links": {
    "self": {"href": "[1]"}
  }
}

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

Aorders/123

B/orders/123

Chttp://orders/123

Dorders123

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the leading slash in the href

Using invalid URL formats

The href value should be a valid URI or path starting with a slash for relative paths. /orders/123 is correct.

4fill in blank

hard

Fill both blanks to create a HAL resource with a self link and an embedded orders array.

Rest API

{
  "_links": {
    "[1]": {"href": "/orders"}
  },
  "_embedded": {
    "[2]": []
  }
}

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

Aself

Bitems

Corders

Dlinks

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'links' instead of 'self' for the link key

Using 'items' instead of 'orders' for embedded resource

The _links section needs a self link. The embedded resource name is orders.

5fill in blank

hard

Fill all three blanks to create a HAL resource with a self link, embedded orders, and a property 'count' with value 5.

Rest API

{
  "_links": {
    "[1]": {"href": "/orders"}
  },
  "_embedded": {
    "[2]": []
  },
  "[3]": 5
}

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

Aself

Borders

Ccount

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'items' instead of 'orders' for embedded resource

Using '_count' instead of 'count' for the property name

The _links section needs a self link. The embedded resource is orders. The property count holds the number 5.

Practice

1. What is the main purpose of the _links section in a HAL formatted REST API response?

easy

A. To define the API version number

B. To store user authentication tokens

C. To list all data fields in the response

D. To provide URLs to related resources for easy navigation

Solution

1. Step 1: Understand the role of _links in HAL

   The _links section contains URLs pointing to related resources, helping clients navigate the API easily.

2. Step 2: Compare options with HAL purpose

   Options B, C, and D do not describe navigation or linking related resources, which is the key feature of _links.

3. Final Answer:

   To provide URLs to related resources for easy navigation -> Option D

4. Quick Check:

   HAL _links = URLs for related resources [OK]

Hint: Remember: _links always holds related resource URLs [OK]

Common Mistakes:

• Confusing _links with data fields
• Thinking _links stores authentication info
• Assuming _links defines API version

2. Which of the following is the correct way to represent a link to a 'self' resource in HAL JSON?

easy

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

B. "links": { "self": "/orders/123" }

C. "_links": { "self": "/orders/123" }

D. "_link": { "href": "/orders/123" }

Solution

1. Step 1: Recall HAL syntax for links

   HAL requires a _links object with named links, each having an href property.

2. Step 2: Check each option's structure

   "_links": { "self": { "href": "/orders/123" } } correctly uses _links with self containing an object with href. Others miss underscores, use wrong keys, or omit href.

3. Final Answer:

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

4. Quick Check:

   HAL link = _links + href [OK]

Hint: HAL links always use _links and href keys [OK]

Common Mistakes:

• Omitting underscore in _links
• Using string instead of object for link value
• Missing href property inside link

3. Given the following HAL JSON snippet, what is the URL to access the customer's details?

{
  "_links": {
    "self": { "href": "/orders/123" },
    "customer": { "href": "/customers/456" }
  },
  "orderNumber": "123"
}

medium

A. /orders/123

B. /customers/456

C. /orders/456

D. /customers/123

Solution

1. Step 1: Identify the customer link in _links

   The customer key has an href value of "/customers/456" which points to the customer's details URL.

2. Step 2: Confirm other options

   self points to the order URL "/orders/123". Other options mix order and customer IDs incorrectly.

3. Final Answer:

   /customers/456 -> Option B

4. Quick Check:

   Customer link = _links.customer.href = /customers/456 [OK]

Hint: Look inside _links for the named resource URL [OK]

Common Mistakes:

• Confusing self with customer link
• Mixing order and customer IDs
• Ignoring the href property

4. Identify the error in this HAL JSON snippet:

{
  "_links": {
    "self": "/orders/123",
    "items": [{ "href": "/items/1" }, { "href": "/items/2" }]
  }
}

medium

A. The JSON is correct as is

B. "items" should be a single object, not an array

C. "self" link should be an object with an "href" property

D. "_links" key should be "links" without underscore

Solution

1. Step 1: Check the structure of the "self" link

   In HAL, each link must be an object with an href property. Here, "self" is a string, which is incorrect.

2. Step 2: Verify other parts

   "items" is correctly an array of link objects. The _links key must have an underscore. So only "self" link is wrong.

3. Final Answer:

   "self" link should be an object with an "href" property -> Option C

4. Quick Check:

   HAL links = objects with href [OK]

Hint: All HAL links must be objects with href keys [OK]

Common Mistakes:

• Using string instead of object for single links
• Removing underscore from _links
• Thinking arrays are not allowed for multiple links

5. You want to design a HAL response for a blog post that includes links to the author and comments. Which JSON structure correctly follows HAL format?

hard

A. {
"title": "My Post",
"_links": {
"self": { "href": "/posts/1" },
"author": { "href": "/users/42" },
"comments": [
{ "href": "/comments/100" },
{ "href": "/comments/101" }
]
}
}

B. {
"title": "My Post",
"links": {
"self": "/posts/1",
"author": "/users/42",
"comments": ["/comments/100", "/comments/101"]
}
}

C. {
"title": "My Post",
"_links": {
"self": "/posts/1",
"author": "/users/42",
"comments": "/comments/100,/comments/101"
}
}

D. {
"title": "My Post",
"_link": {
"self": { "href": "/posts/1" },
"author": { "href": "/users/42" },
"comments": [
{ "href": "/comments/100" },
{ "href": "/comments/101" }
]
}
}

Solution

1. Step 1: Verify the _links key and link objects

   { "title": "My Post", "_links": { "self": { "href": "/posts/1" }, "author": { "href": "/users/42" }, "comments": [ { "href": "/comments/100" }, { "href": "/comments/101" } ] } } correctly uses _links with each link as an object containing href. Multiple comments are an array of link objects.

2. Step 2: Check other options for errors

   { "title": "My Post", "links": { "self": "/posts/1", "author": "/users/42", "comments": ["/comments/100", "/comments/101"] } } uses "links" without underscore and strings instead of objects. { "title": "My Post", "_links": { "self": "/posts/1", "author": "/users/42", "comments": "/comments/100,/comments/101" } } uses strings instead of objects for links. { "title": "My Post", "_link": { "self": { "href": "/posts/1" }, "author": { "href": "/users/42" }, "comments": [ { "href": "/comments/100" }, { "href": "/comments/101" } ] } } uses incorrect key "_link" instead of "_links".

3. Final Answer:

   Option A JSON structure correctly follows HAL format -> Option A

4. Quick Check:

   HAL requires _links with objects having href [OK]

Hint: Use _links with objects and href for all links [OK]

Common Mistakes:

• Missing underscore in _links
• Using strings instead of objects for links
• Wrong key name like _link