Filtering by field values in Rest API - Mini Project: Build & Apply

Filtering by field values

📖 Scenario: You are building a simple REST API that returns a list of books. Users want to filter books by their genre.

🎯 Goal: Create a REST API endpoint that returns only books matching a given genre filter.

📋 What You'll Learn

Create a list of books with exact fields and values

Add a variable to hold the genre filter

Filter the books list by the genre field using the filter variable

Return the filtered list as JSON output

💡 Why This Matters

🌍 Real World

Filtering data by field values is common in APIs to let users get only the data they want.

💼 Career

Backend developers often write code to filter database or API data based on user requests.

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 exact entries
# Your code here

Hint

Make sure to create a list named books with dictionaries for each book as shown.

2

Add a genre filter variable

Create a variable called genre_filter and set it to the string 'Classic'

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 genre_filter exactly to the string 'Classic'.

3

Filter the books by genre

Create a new list called filtered_books that contains only the books from books where the 'genre' field equals 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 filter books by comparing book['genre'] to genre_filter.

4

Print the filtered books as JSON

Import the json module and print the filtered_books list as a JSON string using json.dumps(filtered_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]
# Import json and print filtered_books as JSON
# Your code here

Hint

Use json.dumps to convert filtered_books to a JSON string and print it.

Practice

1. What does filtering by field values in a REST API usually do?

easy

A. Returns all data entries without any filtering

B. Deletes data entries that match the specified field values

C. Updates all data entries regardless of field values

D. Returns only the data entries that match the specified field values

Solution

1. Step 1: Understand filtering purpose

   Filtering is used to get only data that matches certain criteria, not to delete or update.

2. Step 2: Identify filtering effect

   Filtering by field values returns only entries matching those values.

3. Final Answer:

   Returns only the data entries that match the specified field values -> Option D

4. Quick Check:

   Filtering = Select matching data [OK]

Hint: Filtering narrows data to matching entries only [OK]

Common Mistakes:

• Thinking filtering deletes data
• Confusing filtering with updating data
• Assuming filtering returns all data

2. Which of the following is the correct way to filter users by age 30 in a REST API URL?

easy

A. /users?age=30

B. /users/age=30

C. /users?filter=age>30

D. /users/age/30

Solution

1. Step 1: Recognize query parameter syntax

   Filtering uses query parameters after ? with key=value pairs.

2. Step 2: Match correct syntax

   /users?age=30 correctly filters users with age 30.

3. Final Answer:

   /users?age=30 -> Option A

4. Quick Check:

   Query param = ?key=value [OK]

Hint: Use ?field=value to filter in REST API URLs [OK]

Common Mistakes:

• Using slashes instead of query parameters
• Using incorrect filter syntax like > without API support
• Missing the ? before query parameters

3. Given this API call: /products?category=books&available=true, what data will the API return?

medium

A. All products regardless of category or availability

B. Only products in the 'books' category that are available

C. Only products that are unavailable

D. Only products in the 'books' category regardless of availability

Solution

1. Step 1: Analyze query parameters

   The URL filters products where category equals 'books' and available equals true.

2. Step 2: Determine filtering effect

   Both conditions must be met, so only available books are returned.

3. Final Answer:

   Only products in the 'books' category that are available -> Option B

4. Quick Check:

   Multiple filters = AND condition [OK]

Hint: Multiple filters combine with AND by default [OK]

Common Mistakes:

• Ignoring one of the filter conditions
• Assuming filters combine with OR
• Confusing availability true/false

4. You want to filter orders by status 'shipped' using /orders?status=shipped, but the API returns all orders. What is the likely problem?

medium

A. The query parameter should be ?state=shipped instead

B. The URL is missing a trailing slash

C. The API does not support filtering by 'status'

D. The filter value 'shipped' is case-sensitive and should be uppercase

Solution

1. Step 1: Check API documentation for supported filters

   If 'status' is not a supported filter field, the API ignores it and returns all data.

2. Step 2: Evaluate other options

   Changing parameter name or case only works if API supports it; trailing slash usually doesn't affect filtering.

3. Final Answer:

   The API does not support filtering by 'status' -> Option C

4. Quick Check:

   Unsupported filter = no effect [OK]

Hint: Check API docs for allowed filter fields first [OK]

Common Mistakes:

• Assuming any field can be filtered
• Changing URL format without docs
• Ignoring case sensitivity without confirmation

5. You have an API endpoint /employees that supports filtering by department and active status. How would you get all active employees in the 'sales' department?

hard

A. /employees?department=sales&active=true

B. /employees?active=true,department=sales

C. /employees?department=sales|active=true

D. /employees?department=sales;active=true

Solution

1. Step 1: Use correct query parameter syntax

   Query parameters are joined by & and use key=value pairs.

2. Step 2: Combine filters for department and active status

   /employees?department=sales&active=true correctly filters active sales employees.

3. Final Answer:

   /employees?department=sales&active=true -> Option A

4. Quick Check:

   Use & to combine filters [OK]

Hint: Combine filters with & and key=value pairs [OK]

Common Mistakes:

• Using | or ; instead of & to join filters
• Mixing order of parameters incorrectly
• Using invalid separators causing syntax errors