$filter

The $filter query option allows you to filter the results based on conditions. It supports comparison operators, logical operators, string functions, and arithmetic operations.

Basic Usage

GET /users?$filter=age gt 18

Returns users where age is greater than 18.

Comparison Operators

Operator	Description	Example
eq	Equal	$filter=status eq 'active'
ne	Not equal	$filter=status ne 'deleted'
gt	Greater than	$filter=age gt 18
ge	Greater than or equal	$filter=age ge 18
lt	Less than	$filter=price lt 100
le	Less than or equal	$filter=price le 100
in	In a list of values	$filter=status in ('a','b')

Examples

Equal:

GET /users?$filter=status eq 'active'
GET /products?$filter=categoryId eq 5
GET /orders?$filter=isCompleted eq true

Not Equal:

GET /users?$filter=role ne 'admin'
GET /products?$filter=stock ne 0

Greater Than / Less Than:

GET /products?$filter=price gt 50
GET /users?$filter=age ge 21
GET /orders?$filter=total lt 1000
GET /products?$filter=quantity le 10

In Operator:

GET /users?$filter=status in ('active', 'pending')
GET /products?$filter=categoryId in (1, 2, 3)

Logical Operators

Operator	Description	Example
and	Logical AND	$filter=age gt 18 and status eq 'active'
or	Logical OR	$filter=role eq 'admin' or role eq 'mod'

Examples

AND - Both conditions must be true:

GET /users?$filter=age gt 18 and status eq 'active'
GET /products?$filter=price gt 10 and price lt 100
GET /orders?$filter=status eq 'pending' and total gt 500

OR - Either condition must be true:

GET /users?$filter=role eq 'admin' or role eq 'moderator'
GET /products?$filter=category eq 'electronics' or category eq 'computers'

Combining AND and OR with Parentheses:

GET /users?$filter=(role eq 'admin' or role eq 'moderator') and status eq 'active'
GET /products?$filter=inStock eq true and (price lt 50 or onSale eq true)

String Functions

Function	Description	Example
contains(field, 'value')	Field contains substring	$filter=contains(name, 'john')
startswith(field, 'value')	Field starts with string	$filter=startswith(email, 'admin')
endswith(field, 'value')	Field ends with string	$filter=endswith(email, '@gmail.com')
tolower(field)	Convert to lowercase	$filter=tolower(name) eq 'john'
toupper(field)	Convert to uppercase	$filter=toupper(code) eq 'ABC'
length(field)	Get string length	$filter=length(name) gt 5
indexof(field, 'value')	Find position of substring	$filter=indexof(name, 'a') gt 0
substring(field, start)	Extract substring from position	$filter=substring(code, 0) eq 'PRD'

Examples

contains - Search for substring:

GET /users?$filter=contains(name, 'john')
GET /products?$filter=contains(description, 'wireless')
GET /articles?$filter=contains(title, 'tutorial')

startswith - Match beginning of string:

GET /users?$filter=startswith(email, 'admin')
GET /products?$filter=startswith(sku, 'PRD-')

endswith - Match end of string:

GET /users?$filter=endswith(email, '@company.com')
GET /files?$filter=endswith(filename, '.pdf')

tolower/toupper - Case-insensitive comparison:

GET /users?$filter=tolower(name) eq 'john doe'
GET /products?$filter=toupper(category) eq 'ELECTRONICS'

length - Filter by string length:

GET /users?$filter=length(username) ge 5
GET /products?$filter=length(description) gt 100

Combining string functions:

GET /users?$filter=contains(tolower(name), 'john')
GET /products?$filter=startswith(tolower(name), 'apple')

Arithmetic Operators

Operator	Description	Example
add	Addition	$filter=price add 10 gt 100
sub	Subtraction	$filter=stock sub 5 lt 0
mul	Multiplication	$filter=price mul 2 lt 500
div	Division	$filter=total div 2 gt 50
mod	Modulo	$filter=quantity mod 2 eq 0

Examples

GET /products?$filter=price add 10 gt 100
GET /products?$filter=price mul 1.1 lt 500
GET /orders?$filter=total sub discount gt 100
GET /products?$filter=quantity mod 2 eq 0

Filtering on Related Entities

Filter on properties of expanded/related entities using navigation paths:

GET /orders?$filter=customer/country eq 'USA'
GET /products?$filter=category/name eq 'Electronics'
GET /users?$filter=department/isActive eq true

Working with Data Types

Strings

Strings must be enclosed in single quotes:

$filter=name eq 'John'
$filter=status eq 'active'

Numbers

Numbers are used without quotes:

$filter=age eq 25
$filter=price gt 99.99

Booleans

Use true or false without quotes:

$filter=isActive eq true
$filter=isDeleted eq false

Null Values

Use null without quotes:

$filter=deletedAt eq null
$filter=manager ne null

Dates

Use the datetime prefix:

$filter=createdAt gt datetime'2024-01-01T00:00:00'
$filter=orderDate lt datetime'2024-12-31T23:59:59'

Complex Filter Examples

E-commerce product search:

GET /products?$filter=contains(name, 'laptop') and price ge 500 and price le 2000 and inStock eq true

User management:

GET /users?$filter=(role eq 'admin' or role eq 'moderator') and status eq 'active' and lastLogin gt datetime'2024-01-01T00:00:00'

Order filtering:

GET /orders?$filter=status ne 'cancelled' and total gt 100 and customer/country eq 'USA'

Case-insensitive search:

GET /products?$filter=contains(tolower(name), 'phone') or contains(tolower(description), 'phone')

Combining with Other Query Options

GET /products?$filter=price gt 50 and inStock eq true&$select=id,name,price&$orderby=price desc&$top=10

This query:

1. Filters products with price > 50 that are in stock
2. Selects only id, name, and price fields
3. Orders by price descending
4. Returns top 10 results

Notes

• String values must be enclosed in single quotes ('value')
• Field names are case-sensitive
• Parentheses can be used to group conditions and control evaluation order
• Boolean functions like contains, startswith, endswith can be used directly without comparison (implicitly compared to true)