Query parameter versioning in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this API version check?

Given this Python Flask snippet that checks API version from query parameters, what will be the response if the request URL is /api/resource?version=2?

Rest API

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

@app.route('/api/resource')
def resource():
    version = request.args.get('version', '1')
    if version == '1':
        return jsonify({'message': 'Version 1 response'})
    elif version == '2':
        return jsonify({'message': 'Version 2 response'})
    else:
        return jsonify({'error': 'Unsupported version'}), 400

A 500 Internal Server Error

B {"message": "Version 2 response"}

C {"error": "Unsupported version"}

D {"message": "Version 1 response"}

💡 Hint

Check how the version parameter is read and matched in the code.

The code reads the 'version' query parameter. If it is '2', it returns the message for version 2. Since the URL has version=2, option B is correct.

🧠 Conceptual

intermediate

Which HTTP status code is best for unsupported API version?

When a client requests an API version that the server does not support using query parameter versioning, which HTTP status code should the server return?

A 400 Bad Request

B 404 Not Found

C 200 OK

D 500 Internal Server Error

💡 Hint

Think about client errors vs server errors.

A 400 Bad Request indicates the client sent a request with invalid parameters, such as an unsupported version. This is more appropriate than 404 or 500.

🔧 Debug

advanced

Why does this version check always return unsupported version response?

This Flask code is intended to return different responses based on the 'version' query parameter. But it always returns the unsupported version response, even when version=2 is requested. What is the bug?

Rest API

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

@app.route('/api/data')
def data():
    version = request.args.get('version')
    if version == 1:
        return jsonify({'message': 'Version 1 data'})
    elif version == 2:
        return jsonify({'message': 'Version 2 data'})
    else:
        return jsonify({'error': 'Unsupported version'}), 400

A The version variable is a string, but compared to integers 1 and 2, so conditions never match.

B The else block is missing a return statement.

C The jsonify function is used incorrectly without parentheses.

D The route decorator is missing a trailing slash causing routing issues.

💡 Hint

Check the data type of the version variable and the comparisons.

request.args.get returns a string. Comparing string '2' to integer 2 is false, so the code always falls to else.

📝 Syntax

advanced

Which option causes a syntax error in this version check?

Identify which code snippet will cause a syntax error when checking the API version from query parameters.

Rest API

version = request.args.get('version', '1')
if version == '1':
    return 'v1'
elif version == '2':
    return 'v2'
else:
    return 'unsupported'

A

if version == '1':
    return 'v1'

B if version == '1': return 'v1'

C if version = '1': return 'v1'

D

if version == '1'
    return 'v1'

💡 Hint

Remember the difference between assignment and comparison operators.

Option C uses a single equals sign (=) in the if condition, which is assignment and causes a syntax error. Conditions require == for comparison.

🚀 Application

expert

How many distinct responses does this API produce for versions 1 to 3?

Consider this Flask API code snippet that uses query parameter versioning. How many distinct JSON responses can this API produce when the version parameter is 1, 2, or 3?

Rest API

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

@app.route('/api/item')
def item():
    version = request.args.get('version', '1')
    match version:
        case '1':
            return jsonify({'data': 'Item v1'})
        case '2':
            return jsonify({'data': 'Item v2'})
        case '3':
            return jsonify({'data': 'Item v3'})
        case _:
            return jsonify({'error': 'Unsupported version'}), 400

A 4

B 0

C 1

D 3

💡 Hint

Count the distinct JSON responses for versions 1, 2, and 3 only.

For versions 1, 2, and 3, the API returns three distinct JSON objects with 'data' keys. The error response is for other versions, not counted here.

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