Query parameter versioning in Rest API - Step-by-Step Execution

Concept Flow - Query parameter versioning

Client sends request

↓

Check URL for version parameter

↓

Use specified

↓

API version

↓

Process request with chosen version

↓

Send response back

The server checks if the client request URL has a version parameter. If yes, it uses that API version; otherwise, it uses a default version to process the request.

Execution Sample

Rest API

GET /api/resource?version=2

Server reads 'version' param
Uses API version 2
Returns response for v2

This example shows a client requesting API version 2 using a query parameter, and the server responding accordingly.

Execution Table

Step	Request URL	Version Parameter Found?	Version Used	Action
1	/api/resource?version=2	Yes	2	Process request with API version 2
2	/api/resource	No	1 (default)	Process request with default API version 1
3	/api/resource?version=3	Yes	3	Process request with API version 3
4	/api/resource?ver=2	No	1 (default)	Process request with default API version 1

💡 Requests processed based on presence and value of 'version' query parameter; default used if missing or unrecognized.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
request_url	/api/resource?version=2	/api/resource	/api/resource?version=3	/api/resource?ver=2	/api/resource?ver=2
version_param_found	false	true	false	true	false
version_used	1 (default)	2	1 (default)	3	1 (default)

Key Moments - 2 Insights

Why does the server use the default version when the URL has 'ver=2' instead of 'version=2'?

The server looks specifically for the 'version' query parameter. Since 'ver' is different, it is not recognized, so the default version is used (see execution_table row 4).

What happens if the version parameter is missing in the request URL?

If the 'version' parameter is missing, the server uses the default API version to process the request (see execution_table row 2).

Visual Quiz - 3 Questions

Look at the execution_table, what version is used at Step 3?

A 1 (default)

B 2

C 3

D No version used

💡 Hint

Check the 'Version Used' column at Step 3 in the execution_table.

At which step does the server NOT find the 'version' parameter?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look at the 'Version Parameter Found?' column in the execution_table.

If the client sends '/api/resource?version=5', what will the server likely do?

A Use default version 1 always

B Use version 5 if supported

C Ignore the version parameter

D Return an error immediately

💡 Hint

Servers usually use the version parameter value if recognized; see how version 2 and 3 are handled in execution_table.

Concept Snapshot

Query parameter versioning:
- Client adds '?version=x' to URL
- Server reads 'version' parameter
- If found, use that API version
- If missing, use default version
- Allows multiple API versions via URL

Full Transcript

Query parameter versioning means the client tells the server which API version to use by adding a 'version' parameter in the URL. The server checks if this parameter exists. If yes, it uses that version to process the request. If not, it uses a default version. For example, a request to '/api/resource?version=2' uses version 2 of the API. If the parameter is missing or named differently, like 'ver', the server uses the default version. This method helps servers support multiple API versions without changing the URL path.

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