Evaluate Conditional Expression

Question

I have a scenario in which I am saving my "if" conditions in database as a string. For example:

String condition = "(([age] >= 28) && ([nationality] == 'US'))";

OR

String condition = "([age] >= 28)";

Now, I want to evaluate that the user has input the condition syntactically correct. These are example of incorrect syntax:

String condition = "(([age] >= 28) && ([nationality] == 'US')"; //Missed ')' bracket

String condition = "[age] >= 28)"; //Missed Opening bracket '('

Like we have in Evaluate Query Expression. Might be Expression tress can be helpful. But how? Need help in this regard.

Answer 1

Take a look at NCalc. It's a framework for evaluating mathematical expressions.

When the expression has a syntax error, the evaluation will throw an EvaluationException.

try
{
    new Expression("(3 + 2").Evaluate();
}
catch(EvaluationException e)
{
    Console.WriteLine("Error catched: " + e.Message);
}

Though, you can also detect syntax errors before the evaluation by using the HasErrors() method.

Expression e = new Expression("a + b * (");
if(e.HasErrors())
{
    Console.WriteLine(e.Error);
}