Quaero

A small query language that can transform queries into system-specific filters.

Quaero is designed to be web-friendly by using letter-based operators instead of symbols. It's very similar to Microsoft Graph (OData) and SCIM filter syntax. See example queries for some examples.

This repository contains translation implementations for Microsoft Graph, Active Directory (LDAP) and SCIM filters, as well as in-memory predicates.

Supported operators

The language supports a wide range of operators supported by most filter/query languages.

Equality operators

• Equals (eq)
• Not equals (ne)
• Logical negation (not)
• In (in)

Relational operators

• Less than (lt)
• Greater than (gt)
• Less than or equal to (le)
• Greater than or equal to (ge)

Conditional operators

• And (and)
• Or (or)

Functions

• Starts with (sw)
• Ends with (ew)
• Contains (co)

Example queries

Quaero	Microsoft Graph	LDAP	SCIM
age gt 42	age gt 42	(age>=43)	age gt 42
age ge 42	age ge 42	(age>=42)	age ge 42
age lt 42	age lt 42	(age<=41)	age lt 42
age le 42	age le 42	(age<=42)	age le 42
name eq "John"	name eq 'John'	(name=John)	name eq "John"
not(name eq "John")	name ne 'John'	(!(name=John))	name ne "John"
department in ["Retail", "Sales"]	department in ('Retail', 'Sales')	(|(department=Retail)(department=Sales))	(department eq "Retail" or department eq "Sales")
isRead eq false	isRead eq false	(isRead=FALSE)	isRead eq false
mail ew "outlook.com"	endsWith(mail, 'outlook.com')	(mail=*outlook.com)	mail ew "outlook.com"
parent ne null	parent ne null	(parent=*)	parent pr
name pr	name ne null	(name=*)	name pr
id eq "275e50ae-ceb8-4f33-9e68-b3b9dc87ea68"	id eq '275e50ae-ceb8-4f33-9e68-b3b9dc87ea68'	(id=\AE\50\5E\27\B8\CE\33\4F\9E\68\B3\B9\DC\87\EA\68)	id eq "275e50ae-ceb8-4f33-9e68-b3b9dc87ea68"

Usage

Either parse a filter expression from a string using Filter.Parse or Filter.TryParse:

Filter filter = Filter.Parse("age gt 42");

Or manually construct a filter expression using the factory methods on the Filter class:

Filter filter = Filter.GreaterThan("age", 42);

Once the filter has been successfully parsed, it can be optimized by calling the Optimize extension method. This will take care of removing redundancies and shortening the resulting query.

To transform the query into an LDAP filter, reference the Quaero.Ldap package and call the ToLdapFilter method on it:

string result = filter.ToLdapFilter();

For Microsoft Graph, reference the Quaero.MicrosoftGraph package and call ToMicrosoftGraphFilter on the filter:

string result = filter.ToMicrosoftGraphFilter();

And for SCIM, reference the Quaero.Scim package and call ToScimFilter on the filter:

string result = filter.ToScimFilter();

If you want to evaluate a filter in-memory, you can call the ToPredicate<T> method on it:

record Person(string Name, int Age); Func<Person, bool> predicate = filter.ToPredicate<Person>();