Resource identifiers in URLs in Rest API - Step-by-Step Execution

Concept Flow - Resource identifiers in URLs

Client sends request

↓

URL contains resource ID

↓

Server extracts ID from URL

↓

Server finds resource by ID

↓

Server sends resource data back

↓

Client receives specific resource

The client sends a request with a URL containing a resource ID; the server extracts this ID to find and return the specific resource.

Execution Sample

Rest API

GET /users/42 HTTP/1.1
Host: example.com

Response:
HTTP/1.1 200 OK
Content-Type: application/json

{
  "id": 42,
  "name": "Alice"
}

This request asks the server for the user with ID 42, and the server responds with that user's data.

Execution Table

Step	Action	URL Part	Extracted ID	Server Operation	Response
1	Client sends request	/users/42	42	Extract ID 42 from URL	Waiting
2	Server looks up resource	/users/42	42	Find user with ID 42	User data found
3	Server sends response	/users/42	42	Send user data in response	{"id":42,"name":"Alice"}
4	Client receives response	/users/42	42	Display user data	User info shown

💡 Request completed after server sends user data for ID 42

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
URL	N/A	/users/42	/users/42	/users/42	/users/42
Extracted ID	None	42	42	42	42
Server Resource	None	None	User object with ID 42	User object with ID 42	User object with ID 42
Response	None	None	None	{"id":42,"name":"Alice"}	{"id":42,"name":"Alice"}

Key Moments - 3 Insights

Why does the server need to extract the ID from the URL?

The server extracts the ID (see Step 1 in execution_table) to know exactly which resource the client wants, so it can find and return the correct data.

What happens if the ID in the URL does not exist on the server?

If the ID is not found (not shown in this trace), the server would respond with an error like 404 Not Found instead of user data.

Can the resource identifier be something other than a number?

Yes, resource IDs can be strings or other formats, but the server must still extract and use them to find the resource.

Visual Quiz - 3 Questions

Look at the execution_table, what is the Extracted ID at Step 2?

A None

B 42

C /users/42

D User object

💡 Hint

Check the 'Extracted ID' column in row for Step 2 in execution_table.

At which step does the server send the user data back to the client?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Response' column in execution_table to find when data is sent.

If the URL was /users/99 and user 99 does not exist, what would change in the execution_table?

A Server operation would result in error, response would be 404

B Extracted ID would be None

C Server would find user 99 and send data

D Client would not send request

💡 Hint

Think about what happens when the server cannot find the resource by ID.

Concept Snapshot

Resource identifiers in URLs specify which item the client wants.
The server extracts this ID from the URL path.
It uses the ID to find the resource in its data.
The server returns the resource data in the response.
If not found, server returns an error like 404.
Example: GET /users/42 fetches user with ID 42.

Full Transcript

This visual trace shows how resource identifiers in URLs work in REST APIs. The client sends a request with a URL containing an ID, like /users/42. The server extracts the ID '42' from the URL to know which user to find. It then looks up the user with ID 42 in its data. After finding the user, the server sends back the user's data in the response. The client receives and displays this data. If the ID does not exist, the server would respond with an error such as 404 Not Found. This process helps clients get specific resources by using clear, simple URLs.

Practice

1. What is the main purpose of resource identifiers in REST API URLs?

easy

A. To uniquely identify a specific resource

B. To specify the HTTP method used

C. To define the server address

D. To set the response format

Solution

1. Step 1: Understand resource identifiers

   Resource identifiers are unique parts of a URL that point to a specific item or resource.

2. Step 2: Identify their role in REST APIs

   They help the server know exactly which resource the client wants to access or modify.

3. Final Answer:

   To uniquely identify a specific resource -> Option A

4. Quick Check:

   Resource identifiers = unique resource ID [OK]

Hint: Resource IDs point to one item in the URL [OK]

Common Mistakes:

• Confusing resource identifiers with HTTP methods
• Thinking resource identifiers define server location
• Mixing resource identifiers with response formats

2. Which of the following is the correct way to include a resource identifier for a user with ID 42 in a REST API URL?

easy

A. /users#42

B. /users?id=42

C. /users/42/details

D. /users/42

Solution

1. Step 1: Identify the standard REST URL format

   Resource identifiers usually come directly after the resource name separated by a slash.

2. Step 2: Check each option

   /users/42 uses "/users/42" which correctly places the ID after the resource name. /users?id=42 uses a query parameter, which is less common for resource identification. /users/42/details adds extra path which may refer to a sub-resource. /users#42 uses a fragment which is not for resource IDs.

3. Final Answer:

   /users/42 -> Option D

4. Quick Check:

   Resource ID follows resource name with slash [OK]

Hint: Resource ID follows resource name with a slash / [OK]

Common Mistakes:

• Using query parameters instead of path segments
• Adding extra path parts that change meaning
• Using URL fragments (#) for resource IDs

3. Given the URL /products/123/reviews/456, which resource does the identifier 456 represent?

medium

A. Product with ID 456

B. Review with ID 456 for product 123

C. Product with ID 123

D. All reviews for product 456

Solution

1. Step 1: Break down the URL path

   The URL has two resource names: "products" and "reviews" with IDs 123 and 456 respectively.

2. Step 2: Understand the hierarchy

   "reviews/456" comes after "products/123", so 456 is the review ID related to product 123.

3. Final Answer:

   Review with ID 456 for product 123 -> Option B

4. Quick Check:

   Last ID is for last resource in URL [OK]

Hint: Last ID belongs to the last resource named [OK]

Common Mistakes:

• Mixing IDs and thinking 456 is a product ID
• Ignoring resource hierarchy in URL
• Assuming IDs apply to all resources

4. Identify the error in this REST API URL for accessing order 789: /orders/ 789

medium

A. The resource identifier should be before the resource name

B. There should be no slash between resource name and ID

C. The ID should be part of the path, not separate

D. The URL is correct as is

Solution

1. Step 1: Analyze the URL structure

   The URL shows /orders/ and then 789 separately, which suggests the ID is not part of the path.

2. Step 2: Understand correct resource ID placement

   The ID should be directly after the resource name in the same path segment, like /orders/789.

3. Final Answer:

   The ID should be part of the path, not separate -> Option C

4. Quick Check:

   Resource ID must be in the path segment [OK]

Hint: Resource ID must be in the same path segment [OK]

Common Mistakes:

• Placing ID outside the URL path
• Removing the slash between resource and ID
• Thinking resource ID comes before resource name

5. You want to design a REST API URL to access a comment with ID 555 on a post with ID 101. Which URL correctly uses resource identifiers to reflect this nested relationship?

hard

A. /posts/101/comments/555

B. /comments/555/posts/101

C. /posts/comments/555/101

D. /posts/555/comments/101

Solution

1. Step 1: Understand resource hierarchy

   The comment belongs to a post, so the post resource should come first in the URL.

2. Step 2: Check each URL option

   /posts/101/comments/555 correctly places the post ID first, then the comments resource with its ID. Other options mix the order or IDs incorrectly.

3. Final Answer:

   /posts/101/comments/555 -> Option A

4. Quick Check:

   Parent resource ID before child resource ID [OK]

Hint: Parent resource ID comes before child resource ID in URL [OK]

Common Mistakes:

• Reversing parent and child resource order
• Mixing IDs between resources
• Placing IDs in wrong path segments