"Filtering" a collection before starting a Linq query on it

Question

I´m working on some validation code and having some issues with my Linq code.

What I have is a class that validates on a particular attribute (ValidationAttribute). That all works fine, ie the validation works with a class that has some properties decorated with that attribute (or subclasses of it).

What I now want to accomplish is to tell my "validator" class to ignore all properties that are marked with a certain other attribute (let´s call that IgnoreAttribute).

So my question is, how do I first find all the properties with the validation attribute (which I have code for already) but first "filter" that collection to ignore the properties that have the ignore attribute (or actually a List collection).

The code for the validation looks like:

from prop in TypeDescriptor.GetProperties(instance).Cast<PropertyDescriptor>()
                   from attribute in prop.Attributes.OfType<ValidationAttribute>().
                   where attribute.IsValid(prop.GetValue(instance)) == false
                   select new ...etc

I want this code to ignore all attributes contained in a List that I have in the class, ie some sort of filtering on the original set...

Any ideas?

UPDATE:

I guess my question is really this: If I have a class that has its properties decorated with attributes like:

class MyClass

[Required]
public string MyProp { get; set; }

[Required]
[Ignore]
public string MyProp2 { get; set; }

How do I find all the properties that have the validation attribute (required inherits that)) but not the ignore attribute? Although I really wan´t it to ignore a list of attributes and not only the ignore attribute.

Answer 1

Do you need the PropertyDescriptor flexible model? Pretty easy with reflection:

    var filtered = instance.GetType().GetProperties()
        .Where(prop => !Attribute.IsDefined(prop, typeof(IgnoreAttribute)));

Or to do the whole thing:

    var invalid = from prop in instance.GetType().GetProperties()
                   where !Attribute.IsDefined(prop, typeof(IgnoreAttribute))
                   let valAttribs = Attribute.GetCustomAttributes(
                            prop, typeof(ValidationAttribute))
                   where valAttribs != null && valAttribs.Length > 0
                   let value = prop.GetValue(instance, null)
                   from ValidationAttribute valAttrib in valAttribs
                   where !valAttrib.IsValid(value)
                   select new {};

Answer 2

Not Any?

from prop in TypeDescriptor.GetProperties(instance).Cast<PropertyDescriptor>() 
where !prop.Attributes.OfType<IgnoreAttribute>().Any()
from attribute in prop.Attributes.OfType<ValidationAttribute>(). 
where attribute.IsValid(prop.GetValue(instance)) == false 
select new ...etc