How do Data Annotations work?

Question

I use Data Annotations in my ASP.NET MVC 3 project to validate the model. These are extremely convenient but currently they are magic to me. I read that data annotations do

Answer 1

You never call anything to validate the properties. The validation doesn't happen magically on its own. from http://msdn.microsoft.com/en-us/library/dd901590%28v=vs.95%29.aspx

Manually Validating Values

When you do not use the DataGrid control to provide the interface for editing data, the validation attributes are not automatically applied. However, you can manually apply the validation test by using the Validator class. You can call the ValidateProperty method on the set accessor of a property to check the value against the validation attributes for the property. You must also set bothValidatesOnExceptions and NotifyOnValidationError properties to true when data binding to receive validation exceptions from validation attributes. For an example of manually applying validation, see the Data Binding Example below.