Multiple filter parameters in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of filtering with multiple query parameters

Consider a REST API endpoint that filters products by category and price range using query parameters. What is the output when requesting /products?category=books&min_price=10&max_price=20 if the database contains:

• Book A: category=books, price=15
• Book B: category=books, price=25
• Pen: category=stationery, price=5

Rest API

products = [
  {"name": "Book A", "category": "books", "price": 15},
  {"name": "Book B", "category": "books", "price": 25},
  {"name": "Pen", "category": "stationery", "price": 5}
]

filtered = [p for p in products if p["category"] == "books" and 10 <= p["price"] <= 20]
print(filtered)

A [{'name': 'Pen', 'category': 'stationery', 'price': 5}]

B [{'name': 'Book B', 'category': 'books', 'price': 25}]

C []

D [{'name': 'Book A', 'category': 'books', 'price': 15}]

💡 Hint

Filter by category first, then check price range.

Only 'Book A' matches both category 'books' and price between 10 and 20 inclusive.

🧠 Conceptual

intermediate

Understanding multiple filter parameters in REST APIs

When a REST API endpoint supports multiple filter parameters like ?color=red&size=medium, how are these filters usually combined to select results?

A Filters are combined with AND logic, so results must match all filters.

B Filters are combined with OR logic, so results can match any filter.

C Filters are ignored and all results are returned.

D Filters are combined randomly for each request.

💡 Hint

Think about how multiple conditions narrow down results.

Multiple filter parameters usually narrow results, so they are combined with AND logic.

🔧 Debug

advanced

Identify the error in handling multiple filters

This code snippet tries to filter users by age and city from query parameters but returns incorrect results. What is the error?

Rest API

def filter_users(users, age=None, city=None):
    filtered = users
    if age:
        filtered = [u for u in users if u['age'] == age]
    if city:
        filtered = [u for u in users if u['city'] == city]
    return filtered

users = [
    {'name': 'Alice', 'age': 30, 'city': 'NY'},
    {'name': 'Bob', 'age': 25, 'city': 'LA'},
    {'name': 'Carol', 'age': 30, 'city': 'LA'}
]

result = filter_users(users, age=30, city='LA')
print(result)

A The second filter overwrites the first, so only city filter applies.

B The function returns an empty list because users is empty.

C The function raises a TypeError due to wrong parameter types.

D The function filters correctly and returns both conditions.

💡 Hint

Check how the filtered list is updated after each condition.

Each filter uses the original users list instead of the filtered list, so the second filter overwrites the first.

📝 Syntax

advanced

Syntax error in parsing multiple filter parameters

Which option correctly parses multiple filter parameters from a URL query string in Python?

Rest API

from urllib.parse import parse_qs
query = 'type=fruit&type=vegetable&color=red'
params = parse_qs(query)
print(params)

A {'type': 'vegetable', 'color': 'red'}

B {'type': ['fruit', 'vegetable'], 'color': ['red']}

C SyntaxError: invalid syntax

D {'type': ['fruit'], 'color': ['red']}

💡 Hint

parse_qs returns lists for each key.

parse_qs returns a dictionary where each key maps to a list of values, even if only one value exists.

🚀 Application

expert

Combining multiple filters with optional parameters

You want to build a REST API endpoint that filters orders by optional parameters: status, min_total, and max_total. Which code snippet correctly applies all filters only if parameters are provided?

A

filtered = []
for o in orders:
  if status and o['status'] != status:
    continue
  if min_total and o['total'] < min_total:
    continue
  if max_total and o['total'] > max_total:
    continue
  filtered.append(o)

B

filtered = orders
if status:
  filtered = [o for o in orders if o['status'] == status]
if min_total:
  filtered = [o for o in orders if o['total'] >= min_total]
if max_total:
  filtered = [o for o in orders if o['total'] <= max_total]

C

filtered = orders
if status:
  filtered = [o for o in filtered if o['status'] == status]
if min_total:
  filtered = [o for o in filtered if o['total'] >= min_total]
if max_total:
  filtered = [o for o in filtered if o['total'] <= max_total]

D

filtered = orders
if status:
  filtered = [o for o in filtered if o['status'] != status]
if min_total:
  filtered = [o for o in filtered if o['total'] < min_total]
if max_total:
  filtered = [o for o in filtered if o['total'] > max_total]

💡 Hint

Apply filters step by step on the current filtered list.

Option C correctly filters the list cumulatively, applying each filter only if the parameter is given.

Practice

1. What does adding multiple filter parameters in a REST API URL do?
example.com/api/items?color=red&size=medium

easy

A. Returns items that match all filter conditions (color red AND size medium).

B. Returns items that match any one of the filter conditions (color red OR size medium).

C. Returns all items ignoring the filters.

D. Returns an error because multiple filters are not allowed.

Solution

1. Step 1: Understand multiple filters in URL

   Multiple filters joined by & mean the server should apply all conditions together.

2. Step 2: Interpret the example URL

   The URL ?color=red&size=medium means items must be red AND medium size.

3. Final Answer:

   Returns items that match all filter conditions (color red AND size medium). -> Option A

4. Quick Check:

   Multiple filters = AND condition [OK]

Hint: Multiple filters joined by & mean AND condition [OK]

Common Mistakes:

• Thinking filters work as OR instead of AND
• Assuming filters are ignored
• Believing multiple filters cause errors

2. Which of the following is the correct syntax to filter items by category=books and author=doe in a REST API URL?

easy

A. example.com/api/items?category=books;author=doe

B. example.com/api/items?category=books&author=doe

C. example.com/api/items?category=books|author=doe

D. example.com/api/items?category=books author=doe

Solution

1. Step 1: Identify correct separator for multiple filters

   In URLs, multiple query parameters are separated by &.

2. Step 2: Check each option

   Only example.com/api/items?category=books&author=doe uses & correctly between filters.

3. Final Answer:

   example.com/api/items?category=books&author=doe -> Option B

4. Quick Check:

   Use & to separate filters [OK]

Hint: Use & to separate multiple filters in URL [OK]

Common Mistakes:

• Using | or ; instead of &
• Leaving spaces between parameters
• Not using any separator

3. Given the REST API call:
GET /products?color=blue&size=large&in_stock=true
What kind of products will the server return?

medium

A. Products that are blue AND large AND in stock.

B. Products that are blue OR large OR in stock.

C. Products that are either blue or large, ignoring stock status.

D. All products regardless of filters.

Solution

1. Step 1: Understand multiple filters joined by &

   Filters combined with & mean all conditions must be true together.

2. Step 2: Apply to given filters

   Only products that are blue, large, and in stock will be returned.

3. Final Answer:

   Products that are blue AND large AND in stock. -> Option A

4. Quick Check:

   Multiple filters = AND condition [OK]

Hint: Multiple filters joined by & mean AND condition [OK]

Common Mistakes:

• Thinking filters combine with OR
• Ignoring some filters
• Assuming filters are optional

4. You wrote this URL to filter users by age=30 and active=true:
example.com/api/users?age=30&active=true&
But the server returns an error. What is the likely problem?

medium

A. The URL should use commas instead of &.

B. The server does not support filtering by age.

C. The filter values must be in quotes.

D. The trailing & at the end causes a syntax error.

Solution

1. Step 1: Check URL syntax for filters

   A trailing & at the end of query parameters is invalid syntax.

2. Step 2: Understand server error cause

   The server likely rejects the URL because of the extra & with no following parameter.

3. Final Answer:

   The trailing & at the end causes a syntax error. -> Option D

4. Quick Check:

   Trailing & causes error [OK]

Hint: Avoid trailing & in URL query parameters [OK]

Common Mistakes:

• Leaving trailing & at end of URL
• Using commas instead of &
• Assuming quotes are needed around values

5. You want to get all orders from the REST API where status is shipped and total is greater than 100. The API supports filtering by multiple parameters but only exact matches. How can you combine filters to get orders with status=shipped and total>100?

hard

A. Use ?status=shipped&total=100 and filter results manually.

B. Use ?status=shipped&total=gt:100 to specify greater than.

C. Use ?status=shipped&total_min=101 if the API supports range filters.

D. Use ?status=shipped&total>100 directly in URL.

Solution

1. Step 1: Understand API filter limitations

   The API only supports exact matches, so direct > operator is not allowed.

2. Step 2: Use API-supported range filter parameter

   Many APIs use parameters like total_min to filter values greater than a number.

3. Step 3: Combine filters correctly

   Using ?status=shipped&total_min=101 filters orders with status shipped and total greater than 100.

4. Final Answer:

   Use ?status=shipped&total_min=101 if the API supports range filters. -> Option C

5. Quick Check:

   Use API range params for > filters [OK]

Hint: Use API-specific range filters like total_min for > conditions [OK]

Common Mistakes:

• Trying to use > directly in URL
• Assuming all APIs support gt: syntax
• Filtering manually after fetching all data