Why Query parameter versioning in Rest API? - Purpose & Use Cases

The Big Idea

What if one small change could stop your app from breaking every time the API updates?

The Scenario

Imagine you have a website API that many apps use. You want to update the API without breaking the old apps. But you have no clear way to tell which app uses which version.

The Problem

Without versioning, every change risks breaking old apps. You must keep multiple copies of the API or guess which app expects what. This is slow, confusing, and causes many errors.

The Solution

Query parameter versioning lets you add a simple version number in the URL query. This way, the server knows exactly which version the app wants, and can respond correctly without confusion.

Before vs After

✗ Before

GET /api/users
// No version info, server guesses version

✓ After

GET /api/users?version=2
// Server knows to use version 2

What It Enables

It enables smooth updates and backward compatibility by clearly separating API versions in requests.

Real Life Example

A mobile app calls GET /api/products?version=1 to get old data format, while the website calls GET /api/products?version=3 to get the latest features.

Key Takeaways

Manual API updates can break old clients.

Query parameter versioning clearly marks API versions.

This keeps old and new clients happy and working.

Practice

1. What is the main purpose of using query parameter versioning in REST APIs?

easy

A. To change the main URL path for each API version

B. To allow clients to specify which API version they want using a query string

C. To hide the API version from clients

D. To force all clients to use the latest API version only

Solution

1. Step 1: Understand query parameter versioning concept

   Query parameter versioning lets clients add a version number in the URL query string, like ?version=1.

2. Step 2: Identify the purpose of this method

   This allows clients to choose which API version to use without changing the main URL path.

3. Final Answer:

   To allow clients to specify which API version they want using a query string -> Option B

4. Quick Check:

   Query parameter versioning = client selects version [OK]

Hint: Version in query string means client chooses API version [OK]

Common Mistakes:

• Thinking versioning changes the main URL path
• Assuming versioning hides API versions
• Believing all clients must use latest version only

2. Which of the following is the correct way to request version 2 of an API using query parameter versioning?

easy

A. GET /api/resource/version=2

B. GET /api/version/2/resource

C. GET /api/resource?version=2

D. GET /api/resource#version=2

Solution

1. Step 1: Recall query parameter syntax in URLs

   Query parameters come after a question mark ? and use key=value pairs, e.g., ?version=2.

2. Step 2: Match the correct syntax for versioning

   The correct way to specify version 2 is by adding ?version=2 after the resource path.

3. Final Answer:

   GET /api/resource?version=2 -> Option C

4. Quick Check:

   Query param syntax = ?key=value [OK]

Hint: Query parameters start with ? and use key=value [OK]

Common Mistakes:

• Using slashes instead of query parameters
• Using # instead of ? for query parameters
• Placing version inside the URL path incorrectly

3. Given this API endpoint code snippet handling versioning:

def get_data(request):
    version = request.GET.get('version', '1')
    if version == '1':
        return 'Data from v1'
    elif version == '2':
        return 'Data from v2'
    else:
        return 'Unknown version'

What will be the output if the client calls /api/data?version=2?

medium

A. "Data from v2"

B. "Unknown version"

C. "Data from v1"

D. Error: version parameter missing

Solution

1. Step 1: Extract version from query parameters

   The code gets the version from the query string. If missing, it defaults to '1'. Here, version='2'.

2. Step 2: Check version conditions

   Since version is '2', the code returns 'Data from v2'.

3. Final Answer:

   "Data from v2" -> Option A

4. Quick Check:

   version=2 returns v2 data [OK]

Hint: Check query param value matches version condition [OK]

Common Mistakes:

• Assuming default version is always used
• Confusing string and integer comparison
• Expecting error when version is provided

4. Consider this code snippet for versioning:

def api_handler(request):
    version = request.GET['version']
    if version == '1':
        return 'Version 1'
    else:
        return 'Other version'

What error will occur if the client calls /api/data without a version parameter?

medium

A. KeyError because 'version' key is missing

B. SyntaxError in code

C. Returns 'Version 1' by default

D. Returns 'Other version'

Solution

1. Step 1: Understand how version is accessed

   The code uses request.GET['version'] which raises KeyError if 'version' is missing.

2. Step 2: Analyze call without version parameter

   Calling without ?version=... means 'version' key is missing, causing KeyError.

3. Final Answer:

   KeyError because 'version' key is missing -> Option A

4. Quick Check:

   Missing key access causes KeyError [OK]

Hint: Access query keys safely to avoid KeyError [OK]

Common Mistakes:

• Assuming default version is used automatically
• Expecting no error when parameter is missing
• Confusing KeyError with SyntaxError

5. You want to support versions 1 and 2 of your API using query parameter versioning. Version 1 returns a list of users as strings, and version 2 returns a list of user objects with 'name' and 'id'. Which approach correctly handles this in a single endpoint?

hard

A. Return an error if version parameter is missing or unknown

B. Change the URL path to /v1/users and /v2/users instead of query parameters

C. Ignore the version parameter and always return the latest format

D. Use ?version=1 to return ['Alice', 'Bob'], and ?version=2 to return [{'name':'Alice','id':1},{'name':'Bob','id':2}]

Solution

1. Step 1: Understand query parameter versioning usage

   Clients specify version using ?version=1 or ?version=2 in the same URL.

2. Step 2: Return different data formats based on version

   Return simple list of strings for version 1, and detailed objects for version 2, matching client request.

3. Final Answer:

   Use ?version=1 to return ['Alice', 'Bob'], and ?version=2 to return [{'name':'Alice','id':1},{'name':'Bob','id':2}] -> Option D

4. Quick Check:

   Query param version controls response format [OK]

Hint: Return data format based on version query param [OK]

Common Mistakes:

• Changing URL path instead of using query parameters
• Ignoring version parameter and mixing formats
• Returning errors unnecessarily for missing versions