has and belongs to many - rails prevent deletion of child unless parent is being deleted also -

in ruby on rails 4, let's parent has many children. when parent deleted, children must deleted. other that, child shall not deleted unless orphan. how that?

i tried following

class parent < activerecord::base   has_many :children, inverse_of: :parent, dependent: :destroy end  class child < activerecord::base   belongs_to :parent, inverse_of: :children   before_destroy :checks private   def checks     not parent # true if orphan   end end 

with before_destroy check, however, nothing gets deleted. there way of telling method if reason of being called because parent deletion?

is odd thing ask for? mean, preventing deletion of childs.

working carp's answer rails: how disable before_destroy callback when it's being destroyed because of parent being destroyed (:dependent => :destroy), try this:

child:

belongs_to :parent before_destroy :prevent_destroy attr_accessor :destroyed_by_parent  ...  private  def prevent_destroy   if !destroyed_by_parent     self.errors[:base] << "you may not delete child."     return false   end end 

parent:

has_many :children, :dependent => :destroy before_destroy :set_destroyed_by_parent, prepend: true  ...  private  def set_destroyed_by_parent   children.each{ |child| child.destroyed_by_parent = true } end 

we had because we're using paranoia, , dependent: delete_all hard-delete rather soft-delete them. gut tells me there's better way this, it's not obvious, , gets job done.