contract/contract_price_revision/models/contract_line.py

# Copyright 2019 Tecnativa - Vicent Cubells
# Copyright 2019 Tecnativa - Carlos Dauden
# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl.html).

from odoo import api, fields, models
import odoo.addons.decimal_precision as dp


class ContractLine(models.Model):
    _inherit = 'contract.line'

    previous_price = fields.Float(
        string='Previous price',
        related='predecessor_contract_line_id.price_unit',
        readonly=True,
    )
    variation_percent = fields.Float(
        compute='_compute_variation_percent',
        store=True,
        digits=dp.get_precision('Product Price'),
        string='Variation %',
    )

    @api.depends('price_unit', 'predecessor_contract_line_id.price_unit')
    def _compute_variation_percent(self):
        for line in self:
            if line.price_unit and line.previous_price:
                line.variation_percent = (
                    (line.price_unit / line.previous_price - 1) * 100)
            else:
                line.variation_percent = 0.0