> Yes, because a parent without a child has not sense in my application.
>
> So, I want to avoid that possibility.

From a database perspective your request would only be possible solution is to reverse the references -- treat the "Child" as the parent object with the "Parent" being the children object.

In your application, only allow "Parent" to be created from the "Child".


Sean

P.S. Which statement is more "illogical" (1) Child without Parent or (2) Person without a Child. Biologically, #1 is impossible. So, you are really trading one problem for another (How can a Child not have a Parent?).