Laravel ignore validation while updating record

问题

Validation for my model looks like:

public static $rules = array(
    'email' => 'required',
    'password' => 'required'
);

How can i tell laravel not to check the validation for "password" field if user is going to update the record and also i want to retain the previous password in the database until user fills the password again from the edit form?

来源：https://stackoverflow.com/questions/24387300/laravel-ignore-validation-while-updating-record