MVC :: Validate Entity With List?

Let's say we have a entity to add - an Invoice with multiple Lines

public class Lines
{
public string ObjectName;
public string Color;
}
public class Invoice
{
public string DocumentID;
public DateTime InvoiceDate;
public List<Lines> lines;
public string Observation;
}

The Lines is valid if and only if it has ObjectName and Color

Now, when in AddMode , the requirements are to show enter a new Invoice with 10 Lines by default .

This was easy (binding to an object that contains list, right?) - but in validation mode, the ModelState.IsValid is validating all my 10 lines - regardless if the user have been entered only 2 lines.

I have tried to remove the empty lines by writing a Binder for Invoice, inheriting from DefaultModelBinder and removing the empty lines ( those for ObjectName AND Color both nulls or empty ) .But, no matter what overriding method (CreateModel , BindModel ) I have used , no success. The binding model occurs first.

I have tried to do ModelState.Clear() and ValidateModel(invoice) in the controller. But ValidateModel is not validating "sub-properties of complex properties" - see comments from

[URL]

If you know how to either :

a) re-validate all properties (including for complex object)

b) modifying the model before ModelState grab errors

c) ?

(I can not debug with MVC2 source code - but this is another post...)