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

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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.