Suppose I have a field called isbn on stock_move, this field is of Boolean type, I can create a method, with domain filter, which will bring all the stock_move objects, with ('isbn', '=', 'True'),, and reflect that calculation on another field, like this:

@api.multi
@api.depends('stock_move')
def _compute_amount_total(self):
    draft_orders = self.env['stock.move'].search([('isbn', '=', True)])
    product_uom_qty = sum(draft_orders.mapped('product_uom_qty'))
    for record in self:
        record.total_isbn = product_uom_qty

So, by far, this is a nice approach, but now, suppose I want to do this, but not for ALL the stock_movesin which the isbn field is checked, but just for the stock_moves I'm calling from let's say 4 Many2onefields in a model, ie:

stock_move1 = fields.Many2one('stock.move', string="My Stock Move 1")
stock_move2 = fields.Many2one('stock.move', string="My Stock Move 2")
stock_move3 = fields.Many2one('stock.move', string="My Stock Move 3")
stock_move4 = fields.Many2one('stock.move', string="My Stock Move 4")

I can call the isbn field on my model like this though:

stock_move1 = fields.Many2one('stock.move', string="My Stock Move 1")
isbn1 = fields.Boolean(string="ISBN 1", related="stock_move1.isbn")
stock_move2 = fields.Many2one('stock.move', string="My Stock Move 2")
isbn2 = fields.Boolean(string="ISBN 2", related="stock_move2.isbn")
stock_move3 = fields.Many2one('stock.move', string="My Stock Move 3")
isbn3 = fields.Boolean(string="ISBN 3", related="stock_move3.isbn")
stock_move4 = fields.Many2one('stock.move', string="My Stock Move 4")
isbn4 = fields.Boolean(string="ISBN 4", related="stock_move4.isbn")

This should bring them, but actually I don't want to show them or anything on my view, just read those 4 stock_moves look for isbn = True and sum product_uom_qty on them.

I hope I've explained myself.

Any ideas on how this could be accomplished?