Hi,

If you are looking to add sequence number for your model, what you have to do is that,

In the xml,

<record id="seq_sample_name" model="ir.sequence">
    <field name="name">Sample Name</field>
    <field name="code">model_name</field>
    <field name="prefix">PRE</field>
    <field name="padding">3</field>
    <field name="company_id" eval="False"/>
</record>

Then in the Python inside the corresponding model, you can override the create method and assign the sequence number,

@api.model
def create(self, vals):
    if vals.get('name', _('New')) == _('New'):
        vals['name'] = self.env['ir.sequence'].next_by_code('model_name') or _('New')
    res = super(ClassName, self).create(vals)
    return res

Also define a field to assign the sequence,

name = fields.Char(string='Order Reference', required=True, copy=False, readonly=True,
                   index=True, default=lambda self: _('New'))

Thanks