var propertyInfo = typeof(FilterParameter).GetProperty("FilterParameterId");

I think it's impossible to add the attributes dynamically.
You can read this topic.
http://stackoverflow.com/questions/129285/can-attributes-be-added-dynamically-in-c

You can't add attributes. Reflection is read-only on a compiled assembly only.

Why do you want to add the attribute to an existing property? Do you want to compile the assembly again with the new attribute stored?

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Geert van Horrik - CatenaLogic
Visit my blog: http://blog.catenalogic.com

I think it's impossible to add the attributes dynamically.
You can read this topic.
http://stackoverflow.com/questions/129285/can-attributes-be-added-dynamically-in-c

You can't add attributes. Reflection is read-only on a compiled assembly only.

Why do you want to add the attribute to an existing property? Do you want to compile the assembly again with the new attribute stored?

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Geert van Horrik - CatenaLogic
Visit my blog: http://blog.catenalogic.com

This is only relevant to a PropertyGrid. You can customize what it displays with a TypeConverter or a UITypeEditor. Ask questions about this in the Windows Forms Designer forum.

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Hans Passant.

I am using ASP.NET Dynamic Data and I have to add ReadOnly attribute to one of the fields (UpdatedDate) of my class (FilterParameter).

No idea what "dynamic data" means. You can't add attributes to types that are already compiled. I would recommend you post to a more suitable forum, either at forums.asp.net or at the Entity Framework forum at this site.

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Hans Passant.

Thanks.

If you are just trying to do that, consider inheriting from PropertyInfo Class and overriding GetAccessors Method.
This would limit reading the object to your custom class but will give you the functionality you need.