hi ! i am using a sql query to get data into a new module and following is the code

class PostgresReport(models.Model):
    _name = 'purchase.comp'
    _auto = False

    name = fields.Char(string = 'Purchase Order')
    origin = fields.Char(string ='Purchase Agreement')
    date_order = fields.Datetime('Order Date', index=True, copy=False)
    state = fields.Selection([
        ('draft', 'RFQ'),
        ('sent', 'RFQ Sent'),
        ('to approve', 'To Approve'),
        ('purchase', 'Purchase Order'),
        ('done', 'Locked'),
        ('cancel', 'Cancelled')
    ], string='Status', readonly=True, index=True, copy=False, default='draft', track_visibility='onchange')
    product_id = fields.Char(string='Product')
    product_qty = fields.Float(string='Quantity')
    price_unit = fields.Float(string='Unit Price')
    price_subtotal = fields.Monetary(string='Subtotal', store=True)
    vendor = fields.Char(string='Vendor')
    currency_id = fields.Char('Currency')


    @api.model_cr
    def init(self):
        """ Event Question main report """
        tools.drop_view_if_exists(self._cr, 'purchase_comp')
        self._cr.execute(""" CREATE VIEW purchase_comp AS (
               SELECT 
                    b.id as id,
                    a.name as "name",
                    a.origin as "origin",
                    a.date_order as "date_order",
                    a.state as "state",
                    b.name as "product_id",
                    b.product_qty as "product_qty",
                    b.price_unit as "price_unit",
                    b.price_subtotal as "price_subtotal",
                    c.display_name as "vendor",
                    d.name as "currency_id"
                    
    
                FROM public.purchase_order as a
    
                inner join 
                public.purchase_order_line as b
                on a.id = b.order_id
                
                inner join
                public.res_partner as c
                on a.partner_id = c.id
                
                inner join
                public.res_currency  as d
                on d.id = b.currency_id
                
                WHERE a.origin != ''
                order by a.name
        )""")

Now i am trying to fetch its qweb report too but i am unable to get the report of a complete tree view as i have nothing to loop thorugh.Can someone please explain what approach should i use here.