Looking for simple rules-engine library in .NET [closed]

Answer 1

Depending on what you are trying to do using Lambda expressions (and expression trees) can work for this concept. Essentially, you provide an expression as a string that is then compiled on the fly into a lambda expression/expression tree, which you can then execute (evaluate). It's not simple to understand at first, but once you do it's extremely powerful and fairly simple to set up.

Answer 2

Maybe check out SmartRules. Its not free, but the interface looks simple enough.

Only know about it because I've used the SmartCode codegen utility from there before.

Here is an example rule from the Website:

BUSINESS RULES IN NATURAL LANGUAGE      

Before
If (Customer.Age > 50 && Customer.Status == Status.Active) {
policy.SetDiscount(true, 10%);
}

After (with Smart Rules)
If Customer is older than 50 and
the Customer Status is Active Then
Apply 10 % of Discount

Answer 3

It's not free, as you can't easily untangle it from its BizTalk parentage, but the Business Rules Engine components of BizTalk are a separate entity from the core BizTalk engine itself, and comprise a very powerful rules engine that includes a rules / policy based GUI. If there was a free version of this it would fit your requirements (buying BizTalk just for the BRE wouldn't really work commercially.)

Answer 4

Here is a class I have used in the past. It evaluates strings just like eval() does in Javascript.

String result = ExpressionEvaluator.EvaluateToString("(2+5) < 8");

All you need to do is construct a string to be evaluated from your business objects and this will take care of all the complicated nested logic etc.

using System;
using System.CodeDom.Compiler;
using System.Globalization;
using System.Reflection;
using Microsoft.JScript;

namespace Common.Rule
{
  internal static class ExpressionEvaluator
  {
    #region static members
    private static object _evaluator = GetEvaluator();
    private static Type _evaluatorType;
    private const string _evaluatorSourceCode =
        @"package Evaluator
            {
               class Evaluator
               {
                  public function Eval(expr : String) : String 
                  { 
                     return eval(expr); 
                  }
               }
            }";

    #endregion

    #region static methods
    private static object GetEvaluator()
    {
      CompilerParameters parameters;
      parameters = new CompilerParameters();
      parameters.GenerateInMemory = true;

      JScriptCodeProvider jp = new JScriptCodeProvider();
      CompilerResults results = jp.CompileAssemblyFromSource(parameters, _evaluatorSourceCode);

      Assembly assembly = results.CompiledAssembly;
      _evaluatorType = assembly.GetType("Evaluator.Evaluator");

      return Activator.CreateInstance(_evaluatorType);
    }

    /// <summary>
    /// Executes the passed JScript Statement and returns the string representation of the result
    /// </summary>
    /// <param name="statement">A JScript statement to execute</param>
    /// <returns>The string representation of the result of evaluating the passed statement</returns>
    public static string EvaluateToString(string statement)
    {
      object o = EvaluateToObject(statement);
      return o.ToString();
    }

    /// <summary>
    /// Executes the passed JScript Statement and returns the result
    /// </summary>
    /// <param name="statement">A JScript statement to execute</param>
    /// <returns>The result of evaluating the passed statement</returns>
    public static object EvaluateToObject(string statement)
    {
      lock (_evaluator)
      {
        return _evaluatorType.InvokeMember(
                    "Eval",
                    BindingFlags.InvokeMethod,
                    null,
                    _evaluator,
                    new object[] { statement },
                    CultureInfo.CurrentCulture
                 );
      }
    }
    #endregion
  }    
}

Answer 5

You can use a RuEn, an simple open source attribute based Rule Engine created by me:

http://ruen.codeplex.com

Answer 6

None of the open sourced .NET rules-engine have support for storing rules in the database. The only ones that stored the rules in a database are commercial. I've created some UIs for custom rule engines that run off the database, but this can be non-trivial to implement. That's usually the main reason you won't see that feature for free.

As far as I know, none of them will meet all of your criteria, but here is a list of the ones I know of:

Simplest one is SRE
http://sourceforge.net/projects/sdsre/

One with rule management UI is NxBRE
http://www.agilepartner.net/oss/nxbre/

Drools.NET uses JBOSS rules
http://droolsdotnet.codehaus.org/

I personally haven't used any of them, because all of the projects I worked with never wanted to use something built in-house. Most business think that this is pretty easy to do, but end up wasting too much time coding and implementing it. This is one of those areas that the Not Invented Here Syndrome (NIH) rules.