[IMP] core: improve search count with a limit

The new feature (search count with limit) introduced by https://github.com/odoo/odoo/pull/95589 lacks of test and code readability:
- Add tests to check the result and query generate
- Increase the readability of SQL/python code.
- Change a little bit the SQL request generate: in the subquery, change `SELECT 1 FROM...` into `SELECT  FROM` which avoid extra work in the postgreSQL side.

task-2761165

closes odoo/odoo#95641

Signed-off-by: Raphael Collet <rco@odoo.com>

odoo/addons/base/tests/test_expression.py

@@ -1144,12 +1144,25 @@ class TestQueries(TransactionCase):
         Model.search([('name', 'like', 'foo')])
 
         with self.assertQueries(['''
-            SELECT count(*)
+            SELECT COUNT(*)
             FROM "res_partner"
             WHERE (("res_partner"."active" = %s) AND ("res_partner"."name"::text LIKE %s))
         ''']):
             Model.search_count([('name', 'like', 'foo')])
 
+    def test_count_limit(self):
+        Model = self.env['res.partner']
+        Model.search([('name', 'like', 'foo')])
+
+        with self.assertQueries(['''
+            SELECT COUNT(*) FROM (
+                SELECT FROM "res_partner"
+                WHERE (("res_partner"."active" = %s) AND ("res_partner"."name"::text LIKE %s))
+                LIMIT 1
+            ) t
+        ''']):
+            Model.search_count([('name', 'like', 'foo')], limit=1)
+
     def test_translated_field(self):
         self.env['res.lang']._activate_lang('fr_FR')
         Model = self.env['res.partner.title'].with_context(lang='fr_FR')

odoo/addons/base/tests/test_search.py

@@ -192,3 +192,18 @@ class test_search(TransactionCase):
         })
         cc_search = model_bank.search([('name', '=', 'Crédit Communal')])
         self.assertNotIn(bank_credit_communal, cc_search, "Search for inactive record with x_active set to True has failed")
+
+    def test_21_search_count(self):
+        Partner = self.env['res.partner']
+        count_partner_before = Partner.search_count([])
+        partners = Partner.create([
+            {'name': 'abc'},
+            {'name': 'zer'},
+            {'name': 'christope'},
+            {'name': 'runbot'},
+        ])
+        self.assertEqual(len(partners) + count_partner_before, Partner.search_count([]))
+        self.assertEqual(len(partners) + count_partner_before, Partner.search([], count=True))
+
+        self.assertEqual(3, Partner.search_count([], limit=3))
+        self.assertEqual(3, Partner.search([], count=True, limit=3))

odoo/models.py

@@ -1872,6 +1872,10 @@ class BaseModel(metaclass=MetaModel):
 
         Returns the number of records in the current model matching :ref:`the
         provided domain <reference/orm/domains>`.
+
+        :param domain: :ref:`A search domain <reference/orm/domains>`. Use an empty
+                     list to match all records.
+        :param limit: maximum number of record to count (upperbound) (default: all)
         """
         res = self.search(domain, limit=limit, count=True)
         return res if isinstance(res, int) else len(res)
@@ -4888,14 +4892,18 @@ class BaseModel(metaclass=MetaModel):
         query.limit = limit
 
         if count:
-            # Ignore order, limit and offset when just counting, they don't make sense and could
+            # Ignore order and offset when just counting, they don't make sense and could
             # hurt performance
-            query_str, params = query.select(limit and "1" or "count(*)")
             if limit:
-                query_str = "select count(*) from (" + query_str + ") t"
+                # Special case to avoid counting every record in DB (which can be really slow).
+                # The result will be between 0 and limit.
+                query_str, params = query.select("")  # generates a `SELECT FROM` (faster)
+                query_str = f"SELECT COUNT(*) FROM ({query_str}) t"
+            else:
+                query_str, params = query.select("COUNT(*)")
+
             self._cr.execute(query_str, params)
-            res = self._cr.fetchone()
-            return res[0]
+            return self._cr.fetchone()[0]
 
         query.order = self._generate_order_by(order, query).replace('ORDER BY ', '')
         query.offset = offset