Query parameters for filtering in Rest API - Mini Project: Build & Apply

Query Parameters for Filtering in REST API

📖 Scenario: You are building a simple REST API for a bookstore. The API should allow users to get a list of books and filter them by genre using query parameters.

🎯 Goal: Build a REST API endpoint that returns a filtered list of books based on the genre query parameter.

📋 What You'll Learn

Create a list of books with title and genre

Add a query parameter variable to capture the genre filter

Filter the list of books by the genre query parameter

Return the filtered list as JSON output

💡 Why This Matters

🌍 Real World

Filtering data using query parameters is common in APIs to let users get only the information they want.

💼 Career

Understanding query parameters and filtering is essential for backend developers working with REST APIs.

1

Create the initial list of books

Create a list called books with these exact dictionaries: {'title': 'The Hobbit', 'genre': 'Fantasy'}, {'title': '1984', 'genre': 'Dystopian'}, {'title': 'To Kill a Mockingbird', 'genre': 'Classic'}, {'title': 'The Great Gatsby', 'genre': 'Classic'}

Rest API

# Create the list of books with title and genre
# Your code here

Hint

Use a list of dictionaries to store the books with their titles and genres.

2

Add a query parameter variable for genre

Create a variable called genre_filter and set it to the string 'Classic' to simulate receiving a query parameter.

Rest API

books = [
    {'title': 'The Hobbit', 'genre': 'Fantasy'},
    {'title': '1984', 'genre': 'Dystopian'},
    {'title': 'To Kill a Mockingbird', 'genre': 'Classic'},
    {'title': 'The Great Gatsby', 'genre': 'Classic'}
]
# Create a variable genre_filter and set it to 'Classic'
# Your code here

Hint

Set the genre_filter variable to the genre you want to filter by.

3

Filter the books list by genre

Create a new list called filtered_books using a list comprehension that includes only books where the genre matches genre_filter.

Rest API

books = [
    {'title': 'The Hobbit', 'genre': 'Fantasy'},
    {'title': '1984', 'genre': 'Dystopian'},
    {'title': 'To Kill a Mockingbird', 'genre': 'Classic'},
    {'title': 'The Great Gatsby', 'genre': 'Classic'}
]
genre_filter = 'Classic'
# Create filtered_books list with books matching genre_filter
# Your code here

Hint

Use a list comprehension to select books where book['genre'] equals genre_filter.

4

Print the filtered books list

Use print(filtered_books) to display the filtered list of books.

Rest API

books = [
    {'title': 'The Hobbit', 'genre': 'Fantasy'},
    {'title': '1984', 'genre': 'Dystopian'},
    {'title': 'To Kill a Mockingbird', 'genre': 'Classic'},
    {'title': 'The Great Gatsby', 'genre': 'Classic'}
]
genre_filter = 'Classic'
filtered_books = [book for book in books if book['genre'] == genre_filter]
# Print the filtered_books list
# Your code here

Hint

Use print(filtered_books) to show the filtered list.

Practice

1.

What is the main purpose of query parameters in a REST API URL?

easy

A. To update data on the server

B. To change the server settings

C. To filter or specify which data to return

D. To delete data from the server

Solution

1. Step 1: Understand query parameters role

   Query parameters are added after a question mark in a URL to specify or filter data.

2. Step 2: Identify their purpose in REST API

   They help clients ask for specific data subsets, making responses smaller and faster.

3. Final Answer:

   To filter or specify which data to return -> Option C

4. Quick Check:

   Query parameters = filter data [OK]

Hint: Query parameters filter data after '?' in URL [OK]

Common Mistakes:

• Thinking query parameters change server settings
• Confusing query parameters with request body
• Assuming query parameters update or delete data

2.

Which of the following is the correct way to add two query parameters type=fruit and color=red to a REST API URL?

easy

A. api/items?type=fruit,color=red

B. api/items&type=fruit?color=red

C. api/items?type=fruit;color=red

D. api/items?type=fruit&color=red

Solution

1. Step 1: Recall query parameter syntax

   Query parameters start with '?' and multiple parameters are joined with '&'.

2. Step 2: Check each option's format

   api/items?type=fruit&color=red uses '?' then '&' correctly; others misuse separators or order.

3. Final Answer:

   api/items?type=fruit&color=red -> Option D

4. Quick Check:

   Use '?' then '&' between parameters [OK]

Hint: Start with '?' then join parameters with '&' [OK]

Common Mistakes:

• Using '&' before '?'
• Separating parameters with commas or semicolons
• Mixing order of '?' and '&'

3.

Given the URL api/products?category=books&price_lt=20, what does the query parameter price_lt=20 most likely mean?

medium

A. Return products with price less than 20

B. Return products with price equal to 20

C. Return products with price greater than 20

D. Return products with price not equal to 20

Solution

1. Step 1: Interpret the query parameter name

   The suffix '_lt' usually means 'less than' in filtering.

2. Step 2: Apply meaning to the value

   price_lt=20 means filter products priced less than 20 units.

3. Final Answer:

   Return products with price less than 20 -> Option A

4. Quick Check:

   _lt means less than [OK]

Hint: _lt means less than, _gt means greater than [OK]

Common Mistakes:

• Confusing _lt with equal or greater than
• Ignoring suffix meaning in parameter names
• Assuming price_lt filters prices equal to 20

4.

Identify the error in this URL used to filter users by age and city:
api/users?age=30&city;=NewYork

medium

A. The semicolon ';' is incorrectly used instead of '='

B. The '&' should be replaced with '?' between parameters

C. The city value should be URL encoded as 'New%20York'

D. The age parameter should be 'age_gt=30' to filter correctly

Solution

1. Step 1: Check parameter separators and assignments

   Parameters are separated by '&' and assigned with '='. Here, 'city;=NewYork' uses ';' wrongly.

2. Step 2: Confirm correct syntax

   The semicolon should be '=' to assign the value to 'city'.

3. Final Answer:

   The semicolon ';' is incorrectly used instead of '=' -> Option A

4. Quick Check:

   Use '=' to assign values, not ';' [OK]

Hint: Use '=' for assignment, '&' to separate parameters [OK]

Common Mistakes:

• Using semicolon instead of equal sign
• Replacing '&' with '?' between parameters
• Not encoding spaces in values

5.

You want to filter a list of events to show only those happening in 2024 and located in either 'New York' or 'Los Angeles'. Which query parameter format correctly expresses this filter?

hard

A. api/events?year=2024&city=New York,Los Angeles

B. api/events?year=2024&city=New%20York&city=Los%20Angeles

C. api/events?year=2024&city=New York&city=Los Angeles

D. api/events?year=2024&city=New%20York|Los%20Angeles

Solution

1. Step 1: Understand filtering multiple values for one parameter

   To filter by multiple cities, repeat the parameter with URL-encoded values.

2. Step 2: Check URL encoding and parameter repetition

   api/events?year=2024&city=New%20York&city=Los%20Angeles repeats 'city' with URL-encoded spaces, which is standard practice.

3. Final Answer:

   api/events?year=2024&city=New%20York&city=Los%20Angeles -> Option B

4. Quick Check:

   Repeat parameters with URL encoding for multiple values [OK]

Hint: Repeat parameter with encoded values for multiple filters [OK]

Common Mistakes:

• Using commas without encoding or server support
• Not encoding spaces in city names
• Using '|' which is not standard in URLs