Create Foreign Key of ID in Odoo Model Tables

I have two models defined in Odoo. The first model has an ID which automatically created by Odoo when i created a record in it. And then, I need to "link" that ID into my second models once i create it, with the name of main_id. This main_id will act as foreign key in second model.

I see that same approach is achieved between Odoo's product.template and product.product through psql. I can use One2Many to achieve this way, but i don't know how to define the field in Odoo to achieve main_id column that linked to id because i don't define the id by myself.

My First Model :

class FirstModel(models.Model):
    _name = 'first.model'

    user = fields.Many2one("res.user", "Person Name")
    product_lines = fields.One2many('first.model.lines', 'product_id')

My Second Model :

class SecondModel(models.Model):
    _name = 'first.model.lines'

    product_id = fields.Many2one('product.product', string="Product Name")
    product_qty = fields.Integer(string="Qty")

How can I create record in the second model that later has the First Model id as foreign key?

Solution

I found the solution for creating a "Foreign Key" in One2many.

When creating One2many, as Odoo documentation stated it needs something called inverse_name. It should be declared in first model and also the second model. Instead using 'product_id', i create a new variable named 'foreign_key' that later will connect both model as it supposed be.

So the FirstModel would be :

class FirstModel(models.Model):
    _name = 'first.model'

    user = fields.Many2one("res.user", "Person Name")
    product_lines = fields.One2many('first.model.lines', 'foreign_key')

and the SecondModel will be :

class SecondModel(models.Model):
    _name = 'first.model.lines'

    foreign_key = fields.Many2one('combine.product', string="Foreign Key")
    product_id = fields.Many2one('product.product', string="Product Name")
    product_qty = fields.Integer(string="Qty")

As addition, since foreign_key will be automatically added by Odoo, inside .XML files, i hide that foreign_key field so user will not notice and doing things on it.

My XML file :

<field name="product_lines">
   <tree>
      <field name="foreign_key" invisible="1"/>
      <field name="product_id"/>
      <field name="product_qty"/>
   </tree>
</field>