Filtering by field values in Rest API - Step-by-Step Execution

Concept Flow - Filtering by field values

Client sends request with filter parameters

↓

Server receives request

↓

Server extracts filter fields and values

↓

Server queries database or data source

↓

Server applies filter conditions

↓

Server returns filtered data to client

↓

Client receives filtered results

The client sends a request with filter fields; the server extracts these filters, applies them to the data source, and returns only matching results.

Execution Sample

Rest API

GET /api/users?age=30&city=NY

Response:
[
  {"id":1, "name":"Alice", "age":30, "city":"NY"}
]

This request asks the server to return users who are 30 years old and live in NY.

Execution Table

Step	Action	Filter Extracted	Data Source Query	Filtered Result
1	Receive request	age=30, city=NY	Query all users	All users data
2	Apply filter age=30	age=30	Filter users where age=30	Users with age 30
3	Apply filter city=NY	city=NY	Filter users where city=NY	Users with age 30 and city NY
4	Return response	age=30, city=NY	Return filtered users	[{"id":1, "name":"Alice", "age":30, "city":"NY"}]

💡 All filters applied; final filtered data returned to client

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
filters	none	{"age":30}	{"age":30, "city":"NY"}	{"age":30, "city":"NY"}
data_set	all users	users age=30	users age=30 and city=NY	users age=30 and city=NY

Key Moments - 2 Insights

Why do we apply filters one by one instead of all at once?

Applying filters step-by-step (see execution_table rows 2 and 3) helps narrow down data progressively and makes debugging easier.

What happens if a filter field is missing in the request?

If a filter is missing, that condition is skipped, so the server returns data without filtering by that field (not shown in this example but implied).

Visual Quiz - 3 Questions

Look at the execution_table, what is the filtered result after Step 2?

A All users

B Users with age 30

C Users with city NY

D Empty list

💡 Hint

Check the 'Filtered Result' column in row for Step 2

At which step does the server apply the city filter?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column in execution_table

If the client sent only ?city=NY without age, how would the filters variable change after Step 2?

A {"city":"NY"}

B {"age":30}

C {}

D {"age":30, "city":"NY"}

💡 Hint

Refer to variable_tracker 'filters' values and how filters are extracted from request

Concept Snapshot

Filtering by field values in REST API:
- Client sends request with query parameters (e.g., ?age=30&city=NY)
- Server extracts these filters
- Server applies filters to data source
- Server returns only matching data
- Missing filters mean no filtering on that field

Full Transcript

Filtering by field values in REST APIs means the client sends a request with specific fields and values to narrow down data. The server reads these filters, applies them step-by-step to the data source, and returns only the matching results. For example, a request with ?age=30&city=NY will return users who are 30 years old and live in New York. Filters are applied one after another to progressively reduce the data. If a filter is missing, that condition is skipped, and data is not filtered by that field. This process helps clients get only the data they want efficiently.

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