Question

I am new to C# so its quite possible that this has a fairly simple solution but I haven’t found anything I’d consider elegant. If you need any additional information or are confused about what I’m asking in any way, let me know and I will get back to you as soon as I can.

Currently the way create validation rules (for when someone submits a form), like so:

new ValidationRuleInstance<DetailsPresenter>(
    new IsValidDateRule<DetailsPresenter>(m => m.StartDate, "StartDate"),
    new ValidationRuleInterpretation(Severity.Failure, "StartDateMustBeValid", "Must enter valid start date (dd/mm/yyyy)")
),

What I’m attempting to do is create a Validation rule to check if the date that I was give occurred in the past. What I tired is this:

new ValidationRuleInstance<DetailsPresenter>(
    new FailIfTrueRule<DetailsPresenter>(m => (DateTime.Parse(m.StartDate).AddDays(1) < DateTime.Now) ,"StartDate"),
    new ValidationRuleInterpretation(Severity.Failure, "StartDateCannotBeInThePast", "Your start date cannot be in the past")
),

This is works… Most of the time (P.S. I’m adding one day so that entering the current date doesn’t produce an error).

The problem is that if someone submits a String that cannot be parsed into a date time object (eg. 725/2011 instead of 7/25/2011) the whole thing blows up.

I have tried using TryParse, however that returns a Boolean not a Time-Date object.

Am I going to have to write my own method to parse a String and always return a DateTime object? Can I catch the exception and ignore it? (there is a separate rule already in place for checking if the string is valid)

Answer 1

There’s no reason you can’t use a multi-line block of code in a lambda. You just have to enclose the code in brackets and issue explicit return statements, rather than just specifying a single expression that implicitly returns its value.

new ValidationRuleInstance<DetailsPresenter>(
    new FailIfTrueRule<DetailsPresenter>(m => 
{
    DateTime value;

    if(DateTime.TryParse(m.StartDate, out value))
    {
        return value.AddDays(1) < DateTime.Now;
    }
    else // parsing failed, return whatever value is appropriate
    {

    }
} ,"StartDate"),
    new ValidationRuleInterpretation(Severity.Failure, "StartDateCannotBeInThePast", "Your start date cannot be in the past")
),