hi all ,,, i want to add a custom group by filter in order pivot report of point_of_sale in odoo13,
i have added one for a many2one field for the brand of a particular product and its working fine ,,,
now i have a field in product.product named 'style' ,, of type character and i want to add one for that field as well but when i click on it ,,, it gives me this error

File "/home/osama/custom/home/programming/src/odoo13/odoo/sql_db.py", line 241, in execute
    res = self._obj.execute (query, params)
psycopg2.errors.UndefinedColumn: column report_pos_order.style_id does not exist
LINE 2: ... report_pos_order "." Price_total ") AS" price_total "," report_po ...
                                                             ^
HINT: Perhaps you meant to reference the column "report_pos_order.style".


here is my code 

class PosInherit (models.Model): 
    _inherit = 'report.pos.order'
 style_id = fields.Char ( 'Style' , readonly = True ) # color = fields.Char ('Color', readonly = True)     # size = fields .Char ('Size', readonly = True) product_brand_id = fields.Many2one ( 'product.brand' , string = "Brand" , readonly = True ) def _select ( self ): return super (PosInherit, self ) ._ select () +
    
    

    

    
        ", pt.product_brand_id as product_brand_id, p.style_id as style" 
def _group_by ( self ): return super (PosInherit, self ) ._ group_by () + ", pt.product_brand_id, p.style_id"
    
        

<? xml version = "1.0" encoding = "utf-8" ?>
 < odoo > 
    < data > 
        < record id = "pos_inherit_form" model = "ir.ui.view" > 
            < field name = "name" > pos.inherit. form </ field > 
            < field name = "model" > report.pos.order </ field > 
            < field name = "inherit_id" ref = "point_of_sale.
field name = "arch" type = "xml" > 
                < xpath expr = "/ search / filter [@ name = 'not_invoiced']" position = "after" > 
                    < filter string = "Style" name = "style" /> 
                    < filter string = "Color" name = "color" /> 
                    < filter string = "Size" name = "size" /> 
                    <filter string = "Brand" name = "brand"/> 
<! - <field name = "style" /> -> 
<! - <field name = "color" /> -> 
<! - <field name = "size" /> -> 
<! - <field name = "brand_id" /> ->
                     < filter string = "Style" name = "style" context = "{'group_by': 'style_id'}" /> 
<! - <filter string = "Color" name = "color" context = "{'group_by': 'color'}" /> -> 
<! - <filter string = "Size" name = "size" context = "{'group_by' :
                    'size'} "/> -> < filter string =" Brand " name =" brand " context =" {'group_by': 'product_brand_id'} " />

<! - <field name = "style" /> -> 
<! - <field name = "color" /> -> 
<! - <field name = "size" /> ->
                 </ xpath > 
            </ field > 
        </ record > 
    </ data > 
</ odoo >