Multiple filter parameters in Rest API - Step-by-Step Execution

Concept Flow - Multiple filter parameters

Client sends request with multiple filters

↓

Server receives request

↓

Parse each filter parameter

↓

Apply filters to data query

↓

Fetch filtered data

↓

Send filtered data back to client

The server receives a request with several filter parameters, parses them, applies all filters to the data query, then returns the filtered results.

Execution Sample

Rest API

GET /items?color=red&size=medium&in_stock=true

// Server parses filters
filters = {"color": "red", "size": "medium", "in_stock": true}

// Query database with filters
results = db.query(filters)

// Return results

This example shows a client requesting items filtered by color, size, and stock status, and the server processing these filters to return matching items.

Execution Table

Step	Action	Filter Parameters	Query Applied	Result
1	Receive request	color=red, size=medium, in_stock=true	null yet	Waiting to parse filters
2	Parse filters	color=red, size=medium, in_stock=true	null yet	Filters stored as dictionary
3	Apply filters to query	{"color": "red", "size": "medium", "in_stock": true}	SELECT * FROM items WHERE color='red' AND size='medium' AND in_stock=TRUE	Query ready
4	Execute query	{"color": "red", "size": "medium", "in_stock": true}	Same as above	Filtered items fetched
5	Send response	{"color": "red", "size": "medium", "in_stock": true}	N/A	Filtered items sent to client
6	End	N/A	N/A	Request complete

💡 All filters applied; data fetched and response sent to client

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
filters	null	{"color": "red", "size": "medium", "in_stock": true}	{"color": "red", "size": "medium", "in_stock": true}	{"color": "red", "size": "medium", "in_stock": true}
query	null	null	SELECT * FROM items WHERE color='red' AND size='medium' AND in_stock=TRUE	Same as after Step 3
results	null	null	null	List of filtered items

Key Moments - 3 Insights

Why do we parse filter parameters before applying them to the query?

Parsing converts the raw query string into a structured format (like a dictionary) so the server can correctly build the database query, as shown in Step 2 of the execution_table.

What happens if one filter parameter is missing?

The server applies only the filters provided. Missing filters mean those conditions are not included in the query, so more data may be returned. This is implied between Steps 2 and 3.

Why do we combine all filters with AND in the query?

Using AND ensures that only items matching all filter conditions are returned, as shown in the query in Step 3.

Visual Quiz - 3 Questions

Look at the execution_table at Step 3. What does the query include?

A Only the color filter

B All filters combined with AND

C Color and size filters combined with OR

D No filters applied

💡 Hint

Check the 'Query Applied' column at Step 3 in the execution_table

According to variable_tracker, what is the value of 'filters' after Step 2?

A null

B Empty dictionary {}

C {"color": "red", "size": "medium", "in_stock": true}

D List of items

💡 Hint

Look at the 'filters' row under 'After Step 2' in variable_tracker

If the client sends only 'color=blue' as a filter, how would the query change at Step 3?

A SELECT * FROM items WHERE color='blue'

B SELECT * FROM items WHERE size='medium'

C SELECT * FROM items WHERE color='red' AND size='medium'

D No query is made

💡 Hint

Filters in the query match exactly what is parsed from the request (see execution_table Step 3)

Concept Snapshot

Multiple filter parameters let clients narrow data by sending several conditions.
Server parses each filter, then combines them with AND in the query.
Filters are optional; missing ones are ignored.
This helps return only data matching all requested criteria.

Full Transcript

When a client sends a request with multiple filter parameters, the server first receives the request. It then parses the filter parameters into a structured format like a dictionary. Next, the server applies all these filters combined with AND to build a database query. The query fetches only the items matching all filters. Finally, the server sends the filtered data back to the client. This process ensures clients get exactly the data they want by specifying multiple conditions.

Practice

1. What does adding multiple filter parameters in a REST API URL do?
example.com/api/items?color=red&size=medium

easy

A. Returns items that match all filter conditions (color red AND size medium).

B. Returns items that match any one of the filter conditions (color red OR size medium).

C. Returns all items ignoring the filters.

D. Returns an error because multiple filters are not allowed.

Solution

1. Step 1: Understand multiple filters in URL

   Multiple filters joined by & mean the server should apply all conditions together.

2. Step 2: Interpret the example URL

   The URL ?color=red&size=medium means items must be red AND medium size.

3. Final Answer:

   Returns items that match all filter conditions (color red AND size medium). -> Option A

4. Quick Check:

   Multiple filters = AND condition [OK]

Hint: Multiple filters joined by & mean AND condition [OK]

Common Mistakes:

• Thinking filters work as OR instead of AND
• Assuming filters are ignored
• Believing multiple filters cause errors

2. Which of the following is the correct syntax to filter items by category=books and author=doe in a REST API URL?

easy

A. example.com/api/items?category=books;author=doe

B. example.com/api/items?category=books&author=doe

C. example.com/api/items?category=books|author=doe

D. example.com/api/items?category=books author=doe

Solution

1. Step 1: Identify correct separator for multiple filters

   In URLs, multiple query parameters are separated by &.

2. Step 2: Check each option

   Only example.com/api/items?category=books&author=doe uses & correctly between filters.

3. Final Answer:

   example.com/api/items?category=books&author=doe -> Option B

4. Quick Check:

   Use & to separate filters [OK]

Hint: Use & to separate multiple filters in URL [OK]

Common Mistakes:

• Using | or ; instead of &
• Leaving spaces between parameters
• Not using any separator

3. Given the REST API call:
GET /products?color=blue&size=large&in_stock=true
What kind of products will the server return?

medium

A. Products that are blue AND large AND in stock.

B. Products that are blue OR large OR in stock.

C. Products that are either blue or large, ignoring stock status.

D. All products regardless of filters.

Solution

1. Step 1: Understand multiple filters joined by &

   Filters combined with & mean all conditions must be true together.

2. Step 2: Apply to given filters

   Only products that are blue, large, and in stock will be returned.

3. Final Answer:

   Products that are blue AND large AND in stock. -> Option A

4. Quick Check:

   Multiple filters = AND condition [OK]

Hint: Multiple filters joined by & mean AND condition [OK]

Common Mistakes:

• Thinking filters combine with OR
• Ignoring some filters
• Assuming filters are optional

4. You wrote this URL to filter users by age=30 and active=true:
example.com/api/users?age=30&active=true&
But the server returns an error. What is the likely problem?

medium

A. The URL should use commas instead of &.

B. The server does not support filtering by age.

C. The filter values must be in quotes.

D. The trailing & at the end causes a syntax error.

Solution

1. Step 1: Check URL syntax for filters

   A trailing & at the end of query parameters is invalid syntax.

2. Step 2: Understand server error cause

   The server likely rejects the URL because of the extra & with no following parameter.

3. Final Answer:

   The trailing & at the end causes a syntax error. -> Option D

4. Quick Check:

   Trailing & causes error [OK]

Hint: Avoid trailing & in URL query parameters [OK]

Common Mistakes:

• Leaving trailing & at end of URL
• Using commas instead of &
• Assuming quotes are needed around values

5. You want to get all orders from the REST API where status is shipped and total is greater than 100. The API supports filtering by multiple parameters but only exact matches. How can you combine filters to get orders with status=shipped and total>100?

hard

A. Use ?status=shipped&total=100 and filter results manually.

B. Use ?status=shipped&total=gt:100 to specify greater than.

C. Use ?status=shipped&total_min=101 if the API supports range filters.

D. Use ?status=shipped&total>100 directly in URL.

Solution

1. Step 1: Understand API filter limitations

   The API only supports exact matches, so direct > operator is not allowed.

2. Step 2: Use API-supported range filter parameter

   Many APIs use parameters like total_min to filter values greater than a number.

3. Step 3: Combine filters correctly

   Using ?status=shipped&total_min=101 filters orders with status shipped and total greater than 100.

4. Final Answer:

   Use ?status=shipped&total_min=101 if the API supports range filters. -> Option C

5. Quick Check:

   Use API range params for > filters [OK]

Hint: Use API-specific range filters like total_min for > conditions [OK]

Common Mistakes:

• Trying to use > directly in URL
• Assuming all APIs support gt: syntax
• Filtering manually after fetching all data