[IMP] membership: Remove overridden unlink method in favor of an ondelete='cascade'

Removed overridden unlink() of account.invoice/(.line) models by introducing ondelete='cascade'
for 'account_invoice_line' field for 'membership.membership_line' model

addons/membership/models/account_invoice.py

@@ -15,14 +15,6 @@ class Invoice(models.Model):
         ]).write({'date_cancel': fields.Date.today()})
         return super(Invoice, self).action_cancel()
 
-    # TODO master: replace by ondelete='cascade'
-    @api.multi
-    def unlink(self):
-        self.env['membership.membership_line'].search([
-            ('account_invoice_line', 'in', self.mapped('invoice_line_ids').ids)
-        ]).unlink()
-        return super(Invoice, self).unlink()
-
 
 class AccountInvoiceLine(models.Model):
     _inherit = 'account.invoice.line'
@@ -53,16 +45,6 @@ class AccountInvoiceLine(models.Model):
                 member_lines.unlink()
         return res
 
-    # TODO master: replace by ondelete='cascade'
-    @api.multi
-    def unlink(self):
-        """Remove Membership Line Record for Account Invoice Line
-        """
-        self.env['membership.membership_line'].search([
-            ('account_invoice_line', 'in', self.ids)
-        ]).unlink()
-        return super(AccountInvoiceLine, self).unlink()
-
     @api.model
     def create(self, vals):
         MemberLine = self.env['membership.membership_line']

addons/membership/models/membership.py

@@ -30,7 +30,7 @@ class MembershipLine(models.Model):
     member_price = fields.Float(string='Membership Fee',
         digits_compute=dp.get_precision('Product Price'), required=True,
         help='Amount for the membership')
-    account_invoice_line = fields.Many2one('account.invoice.line', string='Account Invoice line', readonly=True)
+    account_invoice_line = fields.Many2one('account.invoice.line', string='Account Invoice line', readonly=True, ondelete='cascade')
     account_invoice_id = fields.Many2one('account.invoice', related='account_invoice_line.invoice_id', string='Invoice', readonly=True)
     company_id = fields.Many2one('res.company', related='account_invoice_line.invoice_id.company_id', string="Company", readonly=True, store=True)
     state = fields.Selection(STATE, compute='_compute_state', string='Membership Status', store=True,