Hello Emad,

We can do a simple trick. Every model has ID field, will generated automatically after saving, before saving this field has no value.

So in your form view of the parent add

<field name="id" invisible="1"/>

then in your o2m field add attrs like :

<field name="o2m_ids" attrs="{'readonly': [('id','=',False)]}">
    <tree editable="bottom">
    ....

I hope it'll help you 

Regards ....