Why Query parameters for filtering in Rest API? - Purpose & Use Cases

The Big Idea

What if you could get exactly what you want instantly, without sifting through endless data?

The Scenario

Imagine you have a huge list of products on a website, and you want to find only the red shirts that are size medium. Without query parameters, you'd have to load the entire list and then search through it manually.

The Problem

This manual method is slow because you download everything first, which wastes time and data. It's also easy to make mistakes by missing items or mixing up filters. Plus, it's frustrating for users who want quick results.

The Solution

Query parameters let you ask the server directly for just the items you want, like "color=red" and "size=medium". This means the server sends only the matching results, making everything faster, simpler, and more accurate.

Before vs After

✗ Before

GET /products
// Then filter results in app code

✓ After

GET /products?color=red&size=medium
// Server returns only matching items

What It Enables

It makes searching and filtering data fast and easy, improving user experience and saving resources.

Real Life Example

When shopping online, you often select filters like brand, price, or rating. These filters use query parameters behind the scenes to show just what you want.

Key Takeaways

Manual filtering loads too much data and wastes time.

Query parameters let servers do the filtering efficiently.

This leads to faster, more accurate, and user-friendly results.

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