From a48beac84544ed2db89ac094cc80508742284c1c Mon Sep 17 00:00:00 2001
From: Guy Marriott <guy@scopey.co.nz>
Date: Mon, 15 Apr 2019 11:36:57 +1200
Subject: [PATCH 1/4] FIX Calculate threshold condition with SQL rather than
 PHP

    This is a performance fix. Modern SQL engines can avoid counting a whole result set (potentially thousands of records) when you are only interested if the count exceeds a threshold.
---
 src/ORM/FieldType/DBForeignKey.php | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/ORM/FieldType/DBForeignKey.php b/src/ORM/FieldType/DBForeignKey.php
index 1c4532204..5071e83e8 100644
--- a/src/ORM/FieldType/DBForeignKey.php
+++ b/src/ORM/FieldType/DBForeignKey.php
@@ -87,12 +87,27 @@ class DBForeignKey extends DBInt
 
         // Add the count of the list to a cache for subsequent calls
         if (!isset(static::$foreignListCache[$hasOneClass])) {
+            // Let the DB do the threshold check as it will be faster - depending on the SQL engine it might only have
+            // to count indexes
+            $dataQuery = $list->dataQuery()->getFinalisedQuery();
+
+            // Clear order-by as it's not relevant for counts
+            $dataQuery->setOrderBy(false);
+            // Remove distinct. Applying distinct shouldn't be required provided relations are not applied.
+            $dataQuery->setDistinct(false);
+
+            $dataQuery->setSelect(['over_threshold' => 'count(*) > ' . (int) $threshold]);
+            $result = $dataQuery->execute()->column('over_threshold');
+            $overThreshold = !empty($result) && ($result[0] === 't' ||  (int) $result[0] === 1);
+
             static::$foreignListCache[$hasOneClass] = [
-                'count' => $list->count(),
+                'overThreshold' => $overThreshold,
             ];
         }
 
-        if (static::$foreignListCache[$hasOneClass]['count'] < $threshold) {
+        $overThreshold = static::$foreignListCache[$hasOneClass]['overThreshold'];
+
+        if (!$overThreshold) {
             // Add the mapped list for the cache
             if (!isset(static::$foreignListCache[$hasOneClass]['map'])) {
                 static::$foreignListCache[$hasOneClass]['map'] = $list->map('ID', $titleField);

From 7fd6e14423dca2f9ff21d90146630f03c3af53bb Mon Sep 17 00:00:00 2001
From: Guy Marriott <guy@scopey.co.nz>
Date: Tue, 16 Apr 2019 12:10:13 +1200
Subject: [PATCH 2/4] Adding comment about the === 't' condition for supporting
 postgres

---
 src/ORM/FieldType/DBForeignKey.php | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/ORM/FieldType/DBForeignKey.php b/src/ORM/FieldType/DBForeignKey.php
index 5071e83e8..d8afaab8c 100644
--- a/src/ORM/FieldType/DBForeignKey.php
+++ b/src/ORM/FieldType/DBForeignKey.php
@@ -98,6 +98,8 @@ class DBForeignKey extends DBInt
 
             $dataQuery->setSelect(['over_threshold' => 'count(*) > ' . (int) $threshold]);
             $result = $dataQuery->execute()->column('over_threshold');
+
+            // Checking for 't' supports PostgreSQL before silverstripe/postgresql@2.2
             $overThreshold = !empty($result) && ($result[0] === 't' ||  (int) $result[0] === 1);
 
             static::$foreignListCache[$hasOneClass] = [

From 80ad336e970c102415d350e92283af4de48bfcf9 Mon Sep 17 00:00:00 2001
From: Guy Marriott <guy@scopey.co.nz>
Date: Thu, 18 Apr 2019 15:31:41 +1200
Subject: [PATCH 3/4] NEW Add API to create a generator from a DataList (#8931)

---
 src/ORM/DataList.php | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/ORM/DataList.php b/src/ORM/DataList.php
index 28f538e9f..9110caabb 100644
--- a/src/ORM/DataList.php
+++ b/src/ORM/DataList.php
@@ -771,6 +771,20 @@ class DataList extends ViewableData implements SS_List, Filterable, Sortable, Li
         return $this;
     }
 
+    /**
+     * Returns a generator for this DataList
+     *
+     * @return \Generator&DataObject[]
+     */
+    public function getGenerator()
+    {
+        $query = $this->dataQuery->query()->execute();
+
+        while ($row = $query->record()) {
+            yield $this->createDataObject($row);
+        }
+    }
+
     public function debug()
     {
         $val = "<h2>" . static::class . "</h2><ul>";

From 86e683c5ecc7919e3958a17aafe406e98bd64914 Mon Sep 17 00:00:00 2001
From: Robbie Averill <robbie@silverstripe.com>
Date: Sun, 21 Apr 2019 11:09:40 +1200
Subject: [PATCH 4/4] Remove obsolete branch alias

---
 composer.json | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/composer.json b/composer.json
index 9185afbbd..70628bb75 100644
--- a/composer.json
+++ b/composer.json
@@ -60,9 +60,6 @@
         "psr/container-implementation": "1.0.0"
     },
     "extra": {
-        "branch-alias": {
-            "4.x-dev": "4.4.x-dev"
-        },
         "expose": [
             "client/images",
             "client/styles",