Calculating the Weighted Average Cost of products stock

Question

I have to calculate my products stock cost, so for every product after each buy, i have to recalculate the Weighted Average Cost.

I got a view thats

Answer 1

Here what i did using function:

CREATE TYPE stock_table_with_wac AS
   (document_type character varying,
    document_date date,
    product_id bigint,
    qty_out double precision,
    qty_in double precision,
    price double precision,
    row_num bigint,
    stock_balance double precision,
    wac double precision);


CREATE OR REPLACE FUNCTION calculate_wac_value()
  RETURNS SETOF stock_table_with_wac AS
$BODY$
    DECLARE
    r_article stock_table_with_wac%rowtype;--maintain the liste of all products with there wac's value
    r_in_out_article stock_table_with_wac%rowtype;--Each other records
    BEGIN
    --For each products
    FOR r_article IN SELECT *, price FROM stock_table where document_type='SI' order by row_num
        LOOP
        return next r_article; 
        FOR r_in_out_article IN SELECT * FROM stock_table where document_type<>'SI' and product_id=r_article.product_id order by row_num
        LOOP
        --If there is an entry calculate the wac
        if r_in_out_article.qty_in >0 then 
            r_in_out_article.wac:=((r_article.price * (r_in_out_article.stock_balance - r_in_out_article.qty_in)) + (r_in_out_article.qty_in * r_in_out_article.price))/(r_in_out_article.stock_balance);       
            --Update the wac value of the product
            r_article.price:= r_in_out_article.wac;
        else --The waca value still inchanged:      
            r_in_out_article.wac:= r_article.price;
        end if;     
            RETURN NEXT r_in_out_article; -- return current row with caluculated wac if any
        END LOOP;
        return next r_article;
        END LOOP;
        RETURN;
    END
    $BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100
  ROWS 1000;
ALTER FUNCTION calculate_wac_value()
  OWNER TO postgres;

select * from calculate_wac_value();

It seems to have a correct output. Is it a good idea to process like this?