A .Net Rule Engine for dynamically evaluating business rules compiled on the fly. If you have business rules that you don't want to hard code then the MicroRuleEngine is your friend. The rule engine is easy to groc and is only about 200 lines of code. Under the covers it creates a Linq expression tree that is compiled so even if your business rules get pretty large or you run them against thousands of items the performance should still compare nicely with a hard coded solution.

Drop the code file into your app and change it as you wish.

The best examples of how to use the MicroRuleEngine (MRE) can be found in the Test project included in the Solution.

One of the tests:

	[TestMethod]
	public void ChildProperties()
	{
		Order order = this.GetOrder();
		Rule rule = new Rule()
		{
			MemberName = "Customer.Country.CountryCode",
			Operator = System.Linq.Expressions.ExpressionType.Equal.ToString("g"),
			TargetValue = "AUS"
		};
		MRE engine = new MRE();
		var compiledRule = engine.CompileRule<Order>(rule);
		bool passes = compiledRule(order);
		Assert.IsTrue(passes);

		order.Customer.Country.CountryCode = "USA";
		passes = compiledRule(order);
		Assert.IsFalse(passes);
	}

In addition to comparative operators such as Equals, GreaterThan, LessThan etc. You can also call methods on the object that return a boolean value such as Contains or StartsWith on a string. In addition to comparative operators, additional operators such as IsMatch or IsInteger have been added and demonstrates how you could edit the code to add your own operator(s). Rules can also be AND'd or OR'd together:

	Rule rule =
		Rule.Create("Customer.LastName", "Contains", "Do")
		& (
			Rule.Create("Customer.FirstName", "StartsWith", "Jo")
			| Rule.Create("Customer.FirstName", "StartsWith", "Bob")
		);

You can reference member properties which are Arrays or List<> by their index:

	Rule rule = Rule.Create("Items[1].Cost", mreOperator.GreaterThanOrEqual, "5.25");

Similarly, you can reference element of a string- or integer-keyed dictionary:

	Rule rule = Rule.Create("Items['myKey'].Cost", mreOperator.GreaterThanOrEqual, "5.25");

You can also compare an object to itself indicated by the *. at the beginning of the TargetValue:

	Rule rule = Rule.Create("Items[1].Cost", mreOperator.Equal, "*.Items[0].Cost");

There are a lot of examples in the test cases but, here is another snippet demonstrating nested OR logic:

	[TestMethod]
	public void ConditionalLogic()
	{
		Order order = this.GetOrder();
		Rule rule = new Rule()
		{
			Operator = "AndAlso",
			Rules = new List<Rule>()
			{
				new Rule() { MemberName = "Customer.LastName", TargetValue = "Doe", Operator = "Equal"},
				new Rule() { 
					Operator = "Or",
					Rules = new List<Rule>() {
						new Rule(){ MemberName = "Customer.FirstName", TargetValue = "John", Operator = "Equal"},
						new Rule(){ MemberName = "Customer.FirstName", TargetValue = "Judy", Operator = "Equal"}
					}
				}
			}
		};
		MRE engine = new MRE();
		var fakeName = engine.CompileRule<Order>(rule);
		bool passes = fakeName(order);
		Assert.IsTrue(passes);

		order.Customer.FirstName = "Philip";
		passes = fakeName(order);
		Assert.IsFalse(passes);
	}

If you need to run your comparison against an ADO.NET DataSet you can also do that as well:

	var dr = GetDataRow();
	// (int) dr["Column2"] == 123 &&  (string) dr["Column1"] == "Test"
	Rule rule = DataRule.Create<int>("Column2", mreOperator.Equal, "123") & DataRule.Create<string>("Column1", mreOperator.Equal, "Test");

You can test a property for a time range from the current time, using the special case #NOW keyword. The member must be a DataTime or DateTime?, and the target value must be a string in the form :#NOW+90D (The sign can be plus or minus, but must be given. The Suffix can be 'S' for Seconds, M for Minutes, H for Hours, D for Days, or Y for Years. The number must be an integer.)

examples:

Rule rule = Rule.Create("OrderDate", mreOperator.GreaterThanOrEqual, "#NOW-90M");

OrderDate must be within the last 90 minutes.

Rule rule = Rule.Create("ExpirationDate", mreOperator.LessThanOrEqual, "#NOW+1Y");

ExpirationDate must be within the next year.

The Rule Class is just a POCO so you can store your rules as serialized XML, JSON, etc.