Validate DateTime with FluentValidator

Have a look at the Fluent Validation documentation http://fluentvalidation.codeplex.com/documentation.

Try adding a RegEx Validator to ensure that the user's input (a string) can be parsed as a date correctly, prior to applying the Less Than Validator.

EDIT

Having run few test cases and looked at the source code for Fluent Validator I concede that the above approach won't work.

The standard error you get is added during the Model Binding phase, which happens before the fluent validation framework can access and check the model.

I assumed that the framework's authors had been clever and were injecting their validation code into the model binding phase. Looks like they aren't.

So the short answer is what you want to do does not appear to be possible.

Answers

As Stewart mentioned, it's not possible to use FluentValidation alone to get in front of the model binding in this way. I'd offer up two ideas/suggestions though:

If you really can't change the ViewModel type from DateTime to string, you could always clear the model state yourself after model binding and then run the validator manually (I'm assuming you've wired FluentValidation to execute automatically after model binding). In scenarios like this, I would change the property to a string, but then use AutoMapper to map that into a DateTime for whatever business object / domain model / service contract request I need it to ultimately become. That way, you get the most flexibility with parsing and conversion on both sides of the model binding.