Hello Himanshu,

Here you need to use the concept of one2many field type of your custom model i.e demo.demo in sale_order

demo_demo.py

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class DemoDemo(models.Model):

    _name = 'demo.demo'

    field1 = 

    field2 = 

    field3 =

    sale_order_id = fields.One2many('sale.order', string="Sale Order")

sale_order.py

---------------------------------------

class SaleOrder(models.Model):

    _inherit = 'sale.order'

    demo_ids = fields.One2many('demo.demo', sale_order_id, string="Demo")

From xml side you need to inherit the sale_order form view i.e "view_order_form"

sale_order_view.xml

--------------------------------

<record id="view_order_form" model="ir.ui.view">

    <field name="name">sale.order.form</field>

    <field name="model">sale.order</field>

    <field name="inherit_id" ref="sale.view_order_form"/>

    <field name="arch" type="xml">

<xpath expr="//form/sheet/notebook" position="inside">

    <page string="Demo Lines">

                <field name="demo_ids">

<tree string="Demo Lines" editable="bottom">

            <field name="field1"/>

            <field name="field2"/>

    <field name="field3"/>

                        </tree>

</field>

   </page>

</xpath>

    </field>

</record>

For detailed information regarding field type in odoo, you may refer this link https://www.cybrosys.com/blog/fields-and-parameters-in-odoo

And for inherit view -> http://learnopenerp.blogspot.com/2018/01/inheritance-in-models-and-views.html

Regards,

Email:   odoo@aktivsoftware.com

Skype: kalpeshmaheshwari

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