[IMP] account_tax_balance: add index

This indexes improve the display time of
account_tax_balance by a factor of 10 on a database
with 1M move lines.

account_tax_balance/__manifest__.py

@@ -5,7 +5,7 @@
 {
     "name": "Tax Balance",
     "summary": "Compute tax balances based on date range",
-    "version": "10.0.1.1.0",
+    "version": "10.0.1.1.1",
     "category": "Accounting & Finance",
     "website": "https://www.agilebg.com/",
     "author": "Agile Business Group, Therp BV, Tecnativa, ACSONE SA/NV, "

account_tax_balance/models/__init__.py

@@ -4,3 +4,4 @@
 
 from . import account_move
 from . import account_tax
+from . import account_move_line

account_tax_balance/models/account_move_line.py

@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 ACSONE SA/NV
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+from odoo import api, models
+
+
+class AccountMoveLine(models.Model):
+
+    _inherit = 'account.move.line'
+
+    @api.model_cr
+    def init(self):
+        res = super(AccountMoveLine, self).init()
+        self._cr.execute("""
+            SELECT indexname FROM pg_indexes
+            WHERE indexname = 'account_move_line_date_tax_line_id_idx'
+        """)
+        if not self._cr.fetchone():
+            self._cr.execute("""
+                CREATE INDEX account_move_line_date_tax_line_id_idx
+                ON account_move_line (date, tax_line_id)
+            """)
+        return res