Date fields coerces invalid dates into valid dates which then passes validation

[kjler]

When using (for example) this property in the model:

 property :birthday, Date, required: true
 validates_primitive_type_of :birthday

and f.date_select :birthday, start_year: Time.now.year, end_year: 1900, prompt: true in the view, Rails/DM will change an invalid date like Year=nil, Day=nil, Month=11 to 0001-11-01, which then passes validation. It's not possible to do a manual validation, since you don't get the raw data in the model.
Only if all of the date parameters birthday(1i), birthday(2i), birthday(3i) is nil will validation fail.