Building a rule engine in c# (part 7: extending the rule engine with a like operator)

In a comment on the rule engine project (ruleengine.codeplex.com) Damien wrote that he would need a like operator in the rule engine to make string compare with wildcards possible. So i added that feature to the rule engine. You now can write “Name like ‘mathi%'” and if the Name property of an object contains the string ‘mathias’ it would return that object. Here is a test that shows the cases that are now possible with the rule engine.

[TestMethod]
public void SimpleExpressionLikeMethod()
{
    Person person1 = new Person()
    {
        Name = "mathias",
        Age = 36,
        Children = 2,
        Married = true,
        Birthdate = new DateTime(1976, 05, 09),
        CancelBenefits = false,
        ReceiveBenefits = false
    };
    Person person2 = new Person()
    {
        Name = "anna",
        Age = 32,
        Children = 2,
        Married = false,
        Birthdate = DateTime.Now,
        CancelBenefits = false,
        ReceiveBenefits = false
    };
    Evaluator evaluator = new Evaluator();
    var result1 = evaluator.Evaluate<Person>(
        " Name like 'math%' ", person1);
    Assert.AreEqual(result1, true);
    var result2 = evaluator.Evaluate<Person>(
        " Name like '?nn?' ", person2);
    Assert.AreEqual(result2, true);
    List<Person> list = new List<Person>() { person1, person2 };
    foreach(var person in list)
    {
        var result = evaluator.Evaluate<Person>(
            " Name like 'mat%' || Name like 'a??a' ", person); 
        if(result)
        {
            Debug.WriteLine(person.Name);
            Assert.AreEqual(result, true);
        }
    }
}

As you see it there are two wildcard that work. The % wildcard can only be used at the end of the text, for example “Name like ‘mat%'”. The ? wildcard can be used in the at any possition, for example “Name like ‘math?ia?'”.

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