Rails model validation on create and update only

Question

If I want to have validation only on create, then I can do

validates_presence_of :password, :on => :create
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Answer 1

By default, the validations run for both create and update. So it should be just:

validates_presence_of :password

The :on key just allows you to choose one of them.

Answer 2

Only write:

validates_presence_of :password

No need...

on => :create

Answer 3

You can use this when you need to disable the validation on some specific operations, such as delete.