In stock module there are two models:

stock.production.lot and stock.picking.in

I would like to export an excel that is a join between the two.They both have product_id(which is a relation to product.product ), so basically what I could do is starting from stock.picking.in a left join on product_id. Since I have tried installing the web export module, but going into select any field and selecting a field from one of the object in the relation(like stock_available), they show empty.