From d140f0ef0e7d9cb3eb4a6ad344ae761936a0a288 Mon Sep 17 00:00:00 2001
From: xmo-odoo <xmo@odoo.com>
Date: Thu, 10 Aug 2017 14:51:27 +0200
Subject: [PATCH] [FIX] prefetch issues on computed/related fields (#18644)

When deciding to prefetch records (getting records from the cache with
no value for the field being fetched), if the field was computed
`determine_value` would just get all records, not limited by the normal
prefetch limit; for large recordsets this would generate gigantic
prefetch lists for records we may not need at all.

Fix by applying the `PREFETCH_MAX` limit to records from the cache as is
done in `_prefetch_field`.

Complementarily, when traversing related fields the prefetch
environment would be lost and every record would get an empty prefetch
environment, so the values would ultimately be read one by one.

Example: select (search) 1000 product.product records, access a
related field (e.g. categ_id) in a loop, on the first iteration the
system would first read 1000 templates, then it would read each
categ_id individually, resulting in >1000 SQL queries rather than the
~2 we would expect.

Fixes #18511
---
 odoo/fields.py |  3 ++-
 odoo/models.py | 17 ++++++++---------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/odoo/fields.py b/odoo/fields.py
index ee9547ca774..745e5effb62 100644
--- a/odoo/fields.py
+++ b/odoo/fields.py
@@ -565,7 +565,7 @@ class Field(object):
         """ Traverse the fields of the related field `self` except for the last
         one, and return it as a pair `(last_record, last_field)`. """
         for name in self.related[:-1]:
-            record = record[name][:1]
+            record = record[name][:1].with_prefetch(record._prefetch)
         return record, self.related_field
 
     def _compute_related(self, records):
@@ -978,6 +978,7 @@ class Field(object):
                 self.compute_value(record)
             else:
                 recs = record._in_cache_without(self)
+                recs = recs.with_prefetch(record._prefetch)
                 self.compute_value(recs)
 
         else:
diff --git a/odoo/models.py b/odoo/models.py
index 5eeef77ef4e..f58ed393eb2 100644
--- a/odoo/models.py
+++ b/odoo/models.py
@@ -3058,10 +3058,6 @@ class BaseModel(object):
                 else:
                     records &= self._in_cache_without(f)
 
-        # prefetch at most PREFETCH_MAX records
-        if len(records) > PREFETCH_MAX:
-            records = records[:PREFETCH_MAX] | self
-
         # fetch records with read()
         assert self in records and field in fs
         records = records.with_prefetch(self._prefetch)
@@ -5232,13 +5228,16 @@ class BaseModel(object):
         return RecordCache(self)
 
     @api.model
-    def _in_cache_without(self, field):
-        """ Make sure ``self`` is present in cache (for prefetching), and return
-            the records of model ``self`` in cache that have no value for ``field``
-            (:class:`Field` instance).
+    def _in_cache_without(self, field, limit=PREFETCH_MAX):
+        """ Return records to prefetch that have no value in cache for ``field``
+            (:class:`Field` instance), including ``self``.
+            Return at most ``limit`` records.
         """
         ids = filter(None, self._prefetch[self._name] - set(self.env.cache[field]))
-        return self.browse(ids)
+        recs = self.browse(ids)
+        if limit and len(recs) > limit:
+            recs = self + (recs - self)[:(limit - len(self))]
+        return recs
 
     @api.model
     def refresh(self):