Filtering by field values in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does filtering by field values mean in a REST API?

It means selecting only the data entries where specific fields match certain values. This helps get just the information you want from a large set.

beginner

How do you usually apply filtering in a REST API request?

You add query parameters to the URL that specify the field names and the values you want to filter by. For example, ?status=active filters results where the status field is 'active'.

beginner

Why is filtering by field values useful in real life?

Imagine you want to see only your unread emails or products in stock. Filtering helps you quickly find just those items without looking through everything.

intermediate

What is a common format for filtering multiple fields in a REST API?

You can add multiple query parameters, like ?status=active&category=books, to get items where status is 'active' and category is 'books'.

beginner

What happens if you don't use filtering in a REST API call?

You get all the data from the server, which can be slow and hard to handle if there is a lot of information. Filtering helps reduce this by sending only what you need.

How do you filter results by a field value in a REST API?

A By modifying the server code directly

B By changing the HTTP method to POST

C By using a different domain name

D By adding query parameters to the URL

Filtering is done by adding query parameters like '?field=value' to the URL.

What does the query parameter '?status=active' do?

A Deletes items with status 'active'

B Returns only items where status is 'active'

C Returns all items except those with status 'active'

D Changes the status of all items to 'active'

It filters the results to include only those with the status field equal to 'active'.

Which of these URLs filters by two fields: status and category?

A /items?filter=status=active,category=books

B /items/status/active/category/books

C /items?status=active&category=books

D /items?status=active|category=books

Using multiple query parameters separated by & is the standard way to filter by multiple fields.

Why is filtering important when requesting data from a REST API?

A To get only the data you need and improve speed

B To increase the amount of data returned

C To change the data on the server

D To avoid using query parameters

Filtering reduces data size and speeds up responses by sending only relevant data.

If you want to see only products priced below $20, what would you do?

A Use a query parameter like '?price_lt=20'

B Send a POST request with price=20

C Filter after receiving all products on the client

D Change the API endpoint to /cheap-products

Many APIs use query parameters like 'price_lt' to filter values less than 20.

Explain how filtering by field values works in a REST API and why it is useful.

Think about how you ask for only certain items from a big list.

Describe how you would filter a list of items by multiple fields in a REST API request.

Remember how URLs can have more than one question mark parameter.

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