Hello

without Inheriting it's not possible, because in sale.order.line we have to keep our custom model field as many2one. 

Note: Jignesh given proper example(Check the Jignesh Mehta reply)

hi sorry to reopen this topic but since 3 days i tried to add sale order line to my custom module but very complicate many error. 

Erreur:

Odoo Server Error

Traceback (most recent call last):

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\convert.py", line 757, in parse

    self._tags[rec.tag](rec, de, mode=mode)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\convert.py", line 662, in _tag_record

    record = model.with_context(rec_context)._load_records([data], self.mode == 'update')

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\models.py", line 3838, in _load_records

    records = self._load_records_create([data['values'] for data in to_create])

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\models.py", line 3752, in _load_records_create

    return self.create(values)

  File "<decorator-gen-32>", line 2, in create

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\api.py", line 452, in _model_create_multi

    return create(self, arg)

  File "c:\program files (x86)\odoo 12.0\server\odoo\addons\base\models\ir_ui_view.py", line 428, in create

    return super(View, self).create(vals_list)

  File "<decorator-gen-3>", line 2, in create

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\api.py", line 452, in _model_create_multi

    return create(self, arg)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\models.py", line 3533, in create

    records = self._create(data_list)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\models.py", line 3619, in _create

    col_val = field.convert_to_column(val, self, stored)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\fields.py", line 1946, in convert_to_column

    value = self.convert_to_cache(value, record)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\fields.py", line 1958, in convert_to_cache

    raise ValueError("Wrong value for %s: %r" % (self, value))

ValueError: Wrong value for ir.ui.view.type: 'field'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\http.py", line 654, in _handle_exception

    return super(JsonRequest, self)._handle_exception(exception)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\http.py", line 312, in _handle_exception

    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\pycompat.py", line 87, in reraise

    raise value

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\http.py", line 696, in dispatch

    result = self._call_function(**self.params)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\http.py", line 344, in _call_function

    return checked_call(self.db, *args, **kwargs)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\service\model.py", line 97, in wrapper

    return f(dbname, *args, **kwargs)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\http.py", line 337, in checked_call

    result = self.endpoint(*a, **kw)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\http.py", line 939, in __call__

    return self.method(*args, **kw)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\http.py", line 517, in response_wrap

    response = f(*args, **kw)

  File "c:\program files (x86)\odoo 12.0\server\odoo\addons\web\controllers\main.py", line 966, in call_button

    action = self._call_kw(model, method, args, {})

  File "c:\program files (x86)\odoo 12.0\server\odoo\addons\web\controllers\main.py", line 954, in _call_kw

    return call_kw(request.env[model], method, args, kwargs)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\api.py", line 749, in call_kw

    return _call_kw_multi(method, model, args, kwargs)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\api.py", line 736, in _call_kw_multi

    result = method(recs, *args, **kwargs)

  File "<decorator-gen-61>", line 2, in button_immediate_install

  File "c:\program files (x86)\odoo 12.0\server\odoo\addons\base\models\ir_module.py", line 73, in check_and_log

    return method(self, *args, **kwargs)

  File "c:\program files (x86)\odoo 12.0\server\odoo\addons\base\models\ir_module.py", line 444, in button_immediate_install

    return self._button_immediate_function(type(self).button_install)

  File "c:\program files (x86)\odoo 12.0\server\odoo\addons\base\models\ir_module.py", line 553, in _button_immediate_function

    modules.registry.Registry.new(self._cr.dbname, update_module=True)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\modules\registry.py", line 86, in new

    odoo.modules.load_modules(registry._db, force_demo, status, update_module)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\modules\loading.py", line 421, in load_modules

    loaded_modules, update_module, models_to_check)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\modules\loading.py", line 313, in load_marked_modules

    perform_checks=perform_checks, models_to_check=models_to_check

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\modules\loading.py", line 222, in load_module_graph

    load_data(cr, idref, mode, kind='data', package=package, report=report)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\modules\loading.py", line 68, in load_data

    tools.convert_file(cr, package.name, filename, idref, mode, noupdate, kind, report)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\convert.py", line 801, in convert_file

    convert_xml_import(cr, module, fp, idref, mode, noupdate, report)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\convert.py", line 864, in convert_xml_import

    obj.parse(doc.getroot(), mode=mode)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\convert.py", line 754, in parse

    self.parse(rec, mode)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\convert.py", line 763, in parse

    exc_info[2]

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\pycompat.py", line 86, in reraise

    raise value.with_traceback(tb)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\convert.py", line 757, in parse

    self._tags[rec.tag](rec, de, mode=mode)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\tools\convert.py", line 662, in _tag_record

    record = model.with_context(rec_context)._load_records([data], self.mode == 'update')

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\models.py", line 3838, in _load_records

    records = self._load_records_create([data['values'] for data in to_create])

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\models.py", line 3752, in _load_records_create

    return self.create(values)

  File "<decorator-gen-32>", line 2, in create

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\api.py", line 452, in _model_create_multi

    return create(self, arg)

  File "c:\program files (x86)\odoo 12.0\server\odoo\addons\base\models\ir_ui_view.py", line 428, in create

    return super(View, self).create(vals_list)

  File "<decorator-gen-3>", line 2, in create

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\api.py", line 452, in _model_create_multi

    return create(self, arg)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\models.py", line 3533, in create

    records = self._create(data_list)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\models.py", line 3619, in _create

    col_val = field.convert_to_column(val, self, stored)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\fields.py", line 1946, in convert_to_column

    value = self.convert_to_cache(value, record)

  File "C:\Program Files (x86)\Odoo 12.0\server\odoo\fields.py", line 1958, in convert_to_cache

    raise ValueError("Wrong value for %s: %r" % (self, value))

odoo.tools.convert.ParseError: "Wrong value for ir.ui.view.type: 'field'" while parsing file:/c:/program files (x86)/odoo 12.0/server/odoo/addons/magazine/views/views.xml:5, near

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

      <field name="name">view.magazine.rapport.tree</field>

      <field name="model">magazine.rapport</field>

      <field name="arch" type="xml">

                <field name="sale_order_line_ids" nolabel="1">

                    <tree string="Rapport Magazine" editable="bottom">

                        <field name="order_partner_id"/>

                        <field name="product_id"/>

                      </tree>

                </field>

    </field>

</record>

Hello Fawad Mazhar,

Try below code

custom.py :-

class CustomModel(models.Model):
    _name = 'custom.model'

    name = fields.Char('Name')
    sale_order_line_ids = fields.One2many('sale.order.line', 'custom_model_id', 'Sale Order Line')


class SaleOrderLine(models.Model):
    _inherit = 'sale.order.line'

    custom_model_id = fields.Many2one('custom.model', 'Custom Model')


custom_view.xml :-

<record id="custom_model_form_view" model="ir.ui.view">
    <field name="name">custom.model.form.view</field>
    <field name="model">custom.model</field>
    <field name="arch" type="xml">
        <form string="Custom Model">
            <group>
                <group>
                    <field name="name"/>
                </group>
                <group/>
            </group>
            <group name="custom_lines" string"Custom Lines">
                <field name="sale_order_line_ids" nolabel="1">
                    <tree editable="bottom">
                        <field name="product_id"/>
                        <field name="name"/>
                        <field name="product_uom_qty"/>
                        <field name="price_unit"/>
                        <field name="price_subtotal"/>
                    </tree>
                </field>
            </group>
        </form>
    </field>
</field>


Hope this will helps you

Thanks,