Does anyone have a working example of dynamic NRules?

Question

I'm looking for a working example of dynamic NRules. Actually, I want to write the rules in a notepad file and want to read them at runtime.

I have been searching it through the internet for last 4 days but didn't find anything.

Any help is appreciable.

Answer 1

NRules is primarily positioned as a rules engine where rules are authored in C#, and compiled into assemblies. There is a companion project https://github.com/NRules/NRules.Language that defines a textual DSL (called Rule#) for expressing rules. It's less feature-complete than C# DSL, but is potentially what you are looking for.

You would still have a project in C# that loads the textual rules from the file system or a DB, and drives the rules engine. You would use https://www.nuget.org/packages/NRules.RuleSharp package for parsing the textual rules into a rule model, and https://www.nuget.org/packages/NRules.Runtime to compile the rule model into an executable form and run the rules.

Given a domain model:

namespace Domain
{
    public class Customer
    {
        public string Name { get; set; }
        public string Email { get; set; }
    }
}

And given a text file with rules called MyRuleFile.txt:

using Domain;

rule "Empty Customer Email"
when
    var customer = Customer(x => string.IsNullOrEmpty(x.Email));
    
then
    Console.WriteLine("Customer email is empty. Customer={0}", customer.Name);

Here is an example of how the rules driver code might look like:

var repository = new RuleRepository();
repository.AddNamespace("System");

//Add references to any assembly that the rules are using, e.g. the assembly with the domain model
repository.AddReference(typeof(Console).Assembly);
repository.AddReference(typeof(Customer).Assembly);

//Load rule files
repository.Load(@"MyRuleFile.txt");

//Compile rules 
var factory = repository.Compile();

//Create a rules session
var session = factory.CreateSession();

//Insert facts into the session
session.Insert(customer);

//Fire rules
session.Fire();

Output:

Customer email is empty. Customer=John Do