What is the best way to evaluate user inputed comparison string against a object?

Question

If I have a user give a string such as

eval= "productId = '100' and (GUID = '100' or (GUID = '200' and productId = '100' ) )"

what would be the best way to use the string to see if a object in memory meets those constraints? For example the following model would evaluate true:

evaluate(eval, new Product{productId ='100', GUID='100'})

Anyone push me in the direction of a design pattern that could accomplish this?

Please read [ask] and take the [tour]. *What is the best....* questions are usually not well received since they inherently ask for an opinion. — Ňɏssa Pøngjǣrdenlarp, Sep 20 '17 at 20:52
taking a step back, why is the user being invited to send information in such a format? Is there not a more structured way to receive it? — ADyson, Sep 20 '17 at 20:55

Eser · Accepted Answer · 2017-09-20T21:03:40.300

Using NCalc and reflection, an Evaluate method can be written like:

public object Evaluate(string exprString, object o)
{
    var dict = o.GetType().GetProperties().ToDictionary(p => p.Name, p => p);

    var expr = new NCalc.Expression(exprString);
    expr.EvaluateParameter += (name, e) =>
    {
        e.Result = dict[name].GetValue(o, null);
    };

    return expr.Evaluate();

}

var res = Evaluate(
             "productId = '100' and (GUID = '100' or (GUID = '200' and productId = '100' ) )", 
             new { productId = "100", GUID = "100" });

OR

var res2 = Evaluate("x + 100 + y", new { x = 10, y = 1 });

PS: Error checks + "public fields" of the given object are ignored for simplicity

Wow, this is powerful. Works perfectly. Thanks! – Chris Chevalier Sep 21 '17 at 12:40 — Chris Chevalier, Sep 21 '17 at 12:40

What is the best way to evaluate user inputed comparison string against a object?

1 Answers1