Query parameters for filtering in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are query parameters in a REST API?

Query parameters are key-value pairs added to the end of a URL to send extra information to the server, often used to filter or sort data.

beginner

How do you add multiple filters using query parameters?

You add multiple filters by separating each key-value pair with an ampersand (&) in the URL, like ?color=red&size=medium.

beginner

Example: What does this URL filter?
/products?category=books&price_lt=20

It filters products to show only those in the 'books' category with a price less than 20.

intermediate

Why use query parameters for filtering instead of sending data in the request body?

Query parameters are part of the URL and are ideal for GET requests to retrieve filtered data without changing server state, while request bodies are used for POST or PUT requests.

intermediate

What is a common naming convention for query parameters used to filter by comparison (e.g., less than, greater than)?

Common conventions add suffixes like _lt (less than), _gt (greater than), _lte (less than or equal to), _gte (greater than or equal to) to the parameter name.

Which symbol starts query parameters in a URL?

A ?

B &

C #

D /

Query parameters start after a question mark (?) in the URL.

How do you separate multiple query parameters?

A &

B ;

C ?

D :

Multiple query parameters are separated by an ampersand (&).

What HTTP method usually uses query parameters for filtering?

A POST

B GET

C PUT

D DELETE

GET requests commonly use query parameters to filter data without changing server state.

What does the query parameter price_gte=10 mean?

A Price is less than 10

B Price equals 10

C Price is greater than or equal to 10

D Price is not 10

The suffix _gte means 'greater than or equal to'.

Which URL filters products by color red and size medium?

A /products?color:red;size:medium

B /products/color/red/size/medium

C /products?red&medium

D /products?color=red&size=medium

Query parameters use key=value pairs separated by &.

Explain how query parameters are used to filter data in a REST API.

Think about how URLs change when you want to see only certain items.

Describe common naming conventions for query parameters that filter by comparison operators.

Suffixes help specify how to compare values.

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