Nested resources in Rest API

Introduction

Nested resources help organize related data in a clear way. They show how one thing belongs inside another.

You have a blog with posts and each post has comments.

You manage a store with categories and products inside each category.

You want to show orders and the items inside each order.

You have users and each user has multiple addresses.

You want to keep track of projects and tasks within each project.

Syntax

Rest API

/parent_resource/{parent_id}/child_resource/{child_id}

The URL shows the child resource inside the parent resource.

IDs help find the exact parent and child items.

Examples

Get comment 456 that belongs to post 123.

Rest API

/posts/123/comments/456

Access address 7 of user 42.

Rest API

/users/42/addresses/7

List all products inside category 5.

Rest API

/categories/5/products

Sample Program

This request asks for chapter 3 inside book 10.

Rest API

GET /books/10/chapters/3 HTTP/1.1
Host: example.com

Important Notes

Nested URLs make it easy to understand relationships between data.

Keep URLs simple and consistent for better API design.

Summary

Nested resources show how one item belongs inside another.

Use nested URLs to organize related data clearly.

Include parent and child IDs to find exact resources.

Practice

1. What is the main purpose of using nested resources in a REST API?

easy

A. To make URLs shorter and simpler

B. To show how one resource belongs inside another resource

C. To avoid using IDs in URLs

D. To separate unrelated data into different APIs

Solution

1. Step 1: Understand nested resources concept

   Nested resources organize data by showing relationships, like a comment inside a post.

2. Step 2: Identify the purpose of nesting

   Nesting clarifies that one resource belongs to another, helping API users find related data easily.

3. Final Answer:

   To show how one resource belongs inside another resource -> Option B

4. Quick Check:

   Nested resources = parent-child relationship [OK]

Hint: Nested URLs show parent-child links clearly [OK]

Common Mistakes:

• Thinking nested resources make URLs shorter
• Believing IDs are not needed in nested URLs
• Confusing unrelated data separation with nesting

2. Which of the following is the correct nested URL format to get comments of a post with ID 5?

easy

A. /comments/5/posts

B. /comments/posts/5

C. /posts/5/comments

D. /posts/comments/5

Solution

1. Step 1: Identify parent and child in URL

   The parent is 'posts' with ID 5, and the child is 'comments'. The child comes after the parent.

2. Step 2: Check URL structure

   The correct format is /parent/{parent_id}/child, so /posts/5/comments is correct.

3. Final Answer:

   /posts/5/comments -> Option C

4. Quick Check:

   Parent ID before child resource [OK]

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

Common Mistakes:

• Placing child resource before parent
• Swapping IDs and resource names
• Using incorrect order of URL segments

3. Given the nested URL /users/10/orders/3, what resource does this URL represent?

medium

A. Order with ID 3 belonging to user with ID 10

B. User with ID 3 who placed order 10

C. All orders of user 10 and order 3 combined

D. User 10's profile and order 3 details merged

Solution

1. Step 1: Analyze URL segments

   The URL shows 'users' with ID 10, then 'orders' with ID 3 nested inside.

2. Step 2: Understand resource relationship

   This means order 3 belongs to user 10, so the URL points to that specific order.

3. Final Answer:

   Order with ID 3 belonging to user with ID 10 -> Option A

4. Quick Check:

   Nested resource = child inside parent [OK]

Hint: Read URL left to right: parent then child with IDs [OK]

Common Mistakes:

• Mixing up which ID belongs to user or order
• Thinking URL shows combined or merged data
• Ignoring the order of resources in URL

4. You have this nested route defined: /projects/{projectId}/tasks/{taskId}. Which URL is incorrect to get task 7 of project 2?

medium

A. /projects/2/tasks/7/

B. /projects/2/tasks/7

C. /projects/2/tasks/07

D. /tasks/7/projects/2

Solution

1. Step 1: Check correct nested URL format

   The correct format is /projects/{projectId}/tasks/{taskId}, so project ID comes before task ID.

2. Step 2: Identify incorrect URL

   /tasks/7/projects/2 reverses the order to /tasks/7/projects/2, which breaks nesting rules.

3. Final Answer:

   /tasks/7/projects/2 -> Option D

4. Quick Check:

   Parent resource must come before child in URL [OK]

Hint: Parent resource always precedes child resource in nested URLs [OK]

Common Mistakes:

• Swapping parent and child in URL
• Adding trailing slashes incorrectly
• Using leading zeros in IDs (usually allowed but check API)

5. You want to design a REST API for a blog where each post has multiple comments, and each comment can have multiple replies. Which nested URL correctly accesses reply 4 of comment 2 on post 10?

hard

A. /posts/10/comments/2/replies/4

B. /posts/10/replies/4/comments/2

C. /comments/2/posts/10/replies/4

D. /posts/10/comments/replies/4/2

Solution

1. Step 1: Understand the resource hierarchy

   Post is the top parent, comments belong to posts, and replies belong to comments.

2. Step 2: Build nested URL from parent to child

   The URL should list post ID, then comment ID, then reply ID in order: /posts/10/comments/2/replies/4.

3. Final Answer:

   /posts/10/comments/2/replies/4 -> Option A

4. Quick Check:

   Nested URL = parent -> child -> grandchild [OK]

Hint: List resources from top parent to deepest child in URL [OK]

Common Mistakes:

• Mixing order of nested resources
• Skipping intermediate resource IDs
• Placing child before parent in URL