From 06b13e0fa621be58c7a9f43ffdc86c071d262fe4 Mon Sep 17 00:00:00 2001
From: Guy Sartorelli <36352093+GuySartorelli@users.noreply.github.com>
Date: Fri, 2 Sep 2022 10:58:37 +1200
Subject: [PATCH] Revert "Merge pull request #10450 from
 creative-commoners/pulls/5/rescue-master-generators" (#10483)

This reverts commit 9edf3a5ca635f9687179143373fe25bddf10c5e3, reversing
changes made to 934fafd29d07a248e00b3055a2ae6d2edab243f6.
---
 src/Forms/GridField/GridFieldExportButton.php |   4 +
 src/ORM/ArrayList.php                         |  23 +-
 src/ORM/Connect/DBSchemaManager.php           |   2 +-
 src/ORM/Connect/MySQLQuery.php                |  35 ++-
 src/ORM/Connect/MySQLStatement.php            |  77 ++++---
 src/ORM/Connect/PDOQuery.php                  |  23 +-
 src/ORM/Connect/Query.php                     | 135 ++++++++++--
 src/ORM/DataList.php                          |  67 +++---
 src/ORM/ListDecorator.php                     |   4 +-
 src/ORM/ManyManyList.php                      |   2 +-
 src/ORM/Map.php                               |  57 ++---
 src/ORM/Map_Iterator.php                      | 200 ++++++++++++++++++
 src/ORM/PaginatedList.php                     |  26 +--
 src/ORM/UnsavedRelationList.php               |   6 +-
 src/View/SSViewer_Scope.php                   |  20 +-
 src/View/ViewableData.php                     |   6 +-
 tests/php/ORM/DatabaseTest.php                |   2 +-
 tests/php/ORM/ListDecoratorTest.php           |   6 +-
 tests/php/ORM/MySQLDatabaseTest.php           |  57 +++--
 tests/php/ORM/PDODatabaseTest.php             |  57 +++--
 tests/php/ORM/PaginatedListTest.php           |  20 +-
 21 files changed, 567 insertions(+), 262 deletions(-)
 create mode 100644 src/ORM/Map_Iterator.php

diff --git a/src/Forms/GridField/GridFieldExportButton.php b/src/Forms/GridField/GridFieldExportButton.php
index 9fc3ad3f36a..9e56b76aad2 100644
--- a/src/Forms/GridField/GridFieldExportButton.php
+++ b/src/Forms/GridField/GridFieldExportButton.php
@@ -223,6 +223,10 @@ public function generateExportFileData($gridField)
 
         // Remove limit as the list may be paginated, we want the full list for the export
         $items = $items->limit(null);
+        // Use Generator in applicable cases to reduce memory consumption
+        $items = $items instanceof DataList
+            ? $items->getGenerator()
+            : $items;
 
         /** @var DataObject $item */
         foreach ($items as $item) {
diff --git a/src/ORM/ArrayList.php b/src/ORM/ArrayList.php
index d8dca3195fe..74a7cd600ea 100644
--- a/src/ORM/ArrayList.php
+++ b/src/ORM/ArrayList.php
@@ -2,8 +2,8 @@
 
 namespace SilverStripe\ORM;
 
+use ArrayIterator;
 use InvalidArgumentException;
-use Iterator;
 use LogicException;
 use SilverStripe\Dev\Debug;
 use SilverStripe\Dev\Deprecation;
@@ -103,16 +103,19 @@ public function exists()
     /**
      * Returns an Iterator for this ArrayList.
      * This function allows you to use ArrayList in foreach loops
+     *
+     * @return ArrayIterator
      */
-    public function getIterator(): Iterator
-    {
-        foreach ($this->items as $i => $item) {
-            if (is_array($item)) {
-                yield new ArrayData($item);
-            } else {
-                yield $item;
-            }
-        }
+    #[\ReturnTypeWillChange]
+    public function getIterator()
+    {
+        $items = array_map(
+            function ($item) {
+                return is_array($item) ? new ArrayData($item) : $item;
+            },
+            $this->items ?? []
+        );
+        return new ArrayIterator($items);
     }
 
     /**
diff --git a/src/ORM/Connect/DBSchemaManager.php b/src/ORM/Connect/DBSchemaManager.php
index 7a10cef8e93..7f93148cbd6 100644
--- a/src/ORM/Connect/DBSchemaManager.php
+++ b/src/ORM/Connect/DBSchemaManager.php
@@ -378,7 +378,7 @@ public function requireTable(
             if ($dbID && isset($options[$dbID])) {
                 if (preg_match('/ENGINE=([^\s]*)/', $options[$dbID] ?? '', $alteredEngineMatches)) {
                     $alteredEngine = $alteredEngineMatches[1];
-                    $tableStatus = $this->query(sprintf('SHOW TABLE STATUS LIKE \'%s\'', $table))->record();
+                    $tableStatus = $this->query(sprintf('SHOW TABLE STATUS LIKE \'%s\'', $table))->first();
                     $tableOptionsChanged = ($tableStatus['Engine'] != $alteredEngine);
                 }
             }
diff --git a/src/ORM/Connect/MySQLQuery.php b/src/ORM/Connect/MySQLQuery.php
index d019167014b..c811386430a 100644
--- a/src/ORM/Connect/MySQLQuery.php
+++ b/src/ORM/Connect/MySQLQuery.php
@@ -2,8 +2,6 @@
 
 namespace SilverStripe\ORM\Connect;
 
-use Iterator;
-
 /**
  * A result-set from a MySQL database (using MySQLiConnector)
  * Note that this class is only used for the results of non-prepared statements
@@ -47,13 +45,16 @@ public function __destruct()
         }
     }
 
-    public function getIterator(): Iterator
+    public function seek($row)
     {
         if (is_object($this->handle)) {
-            while ($data = $this->handle->fetch_assoc()) {
-                yield $data;
-            }
+            // Fix for https://github.com/silverstripe/silverstripe-framework/issues/9097 without breaking the seek() API
+            $this->handle->data_seek($row);
+            $result = $this->nextRecord();
+            $this->handle->data_seek($row);
+            return $result;
         }
+        return null;
     }
 
     public function numRecords()
@@ -61,7 +62,27 @@ public function numRecords()
         if (is_object($this->handle)) {
             return $this->handle->num_rows;
         }
-
         return null;
     }
+
+    public function nextRecord()
+    {
+        $floatTypes = [MYSQLI_TYPE_FLOAT, MYSQLI_TYPE_DOUBLE, MYSQLI_TYPE_DECIMAL, MYSQLI_TYPE_NEWDECIMAL];
+
+        if (is_object($this->handle) && ($row = $this->handle->fetch_array(MYSQLI_NUM))) {
+            $data = [];
+            foreach ($row as $i => $value) {
+                if (!isset($this->columns[$i])) {
+                    throw new DatabaseException("Can't get metadata for column $i");
+                }
+                if (in_array($this->columns[$i]->type, $floatTypes ?? [])) {
+                    $value = (float)$value;
+                }
+                $data[$this->columns[$i]->name] = $value;
+            }
+            return $data;
+        } else {
+            return false;
+        }
+    }
 }
diff --git a/src/ORM/Connect/MySQLStatement.php b/src/ORM/Connect/MySQLStatement.php
index eada8ad407b..7bc54765fcd 100644
--- a/src/ORM/Connect/MySQLStatement.php
+++ b/src/ORM/Connect/MySQLStatement.php
@@ -2,7 +2,6 @@
 
 namespace SilverStripe\ORM\Connect;
 
-use Iterator;
 use mysqli_result;
 use mysqli_stmt;
 
@@ -57,26 +56,6 @@ class MySQLStatement extends Query
      */
     protected $boundValues = [];
 
-    /**
-     * Hook the result-set given into a Query class, suitable for use by SilverStripe.
-     * @param mysqli_stmt $statement The related statement, if present
-     * @param mysqli_result $metadata The metadata for this statement
-     */
-    public function __construct($statement, $metadata)
-    {
-        $this->statement = $statement;
-        $this->metadata = $metadata;
-
-        // Immediately bind and buffer
-        $this->bind();
-    }
-
-    public function __destruct()
-    {
-        $this->statement->close();
-        $this->currentRecord = false;
-    }
-
     /**
      * Binds this statement to the variables
      */
@@ -103,20 +82,58 @@ protected function bind()
         call_user_func_array([$this->statement, 'bind_result'], $variables ?? []);
     }
 
-    public function getIterator(): Iterator
+    /**
+     * Hook the result-set given into a Query class, suitable for use by SilverStripe.
+     * @param mysqli_stmt $statement The related statement, if present
+     * @param mysqli_result $metadata The metadata for this statement
+     */
+    public function __construct($statement, $metadata)
+    {
+        $this->statement = $statement;
+        $this->metadata = $metadata;
+
+        // Immediately bind and buffer
+        $this->bind();
+    }
+
+    public function __destruct()
     {
-        while ($this->statement->fetch()) {
-            // Dereferenced row
-            $row = [];
-            foreach ($this->boundValues as $key => $value) {
-                $row[$key] = $value;
-            }
-            yield $row;
-        }
+        $this->statement->close();
+        $this->currentRecord = false;
+    }
+
+    public function seek($row)
+    {
+        $this->rowNum = $row - 1;
+
+        // Fix for https://github.com/silverstripe/silverstripe-framework/issues/9097 without breaking the seek() API
+        $this->statement->data_seek($row);
+        $result = $this->next();
+        $this->statement->data_seek($row);
+        return $result;
     }
 
     public function numRecords()
     {
         return $this->statement->num_rows();
     }
+
+    public function nextRecord()
+    {
+        // Skip data if out of data
+        if (!$this->statement->fetch()) {
+            return false;
+        }
+
+        // Dereferenced row
+        $row = [];
+        foreach ($this->boundValues as $key => $value) {
+            $floatTypes = [MYSQLI_TYPE_FLOAT, MYSQLI_TYPE_DOUBLE, MYSQLI_TYPE_DECIMAL, MYSQLI_TYPE_NEWDECIMAL];
+            if (in_array($this->types[$key], $floatTypes ?? [])) {
+                $value = (float)$value;
+            }
+            $row[$key] = $value;
+        }
+        return $row;
+    }
 }
diff --git a/src/ORM/Connect/PDOQuery.php b/src/ORM/Connect/PDOQuery.php
index 24f9712eb8a..7180de28d0e 100644
--- a/src/ORM/Connect/PDOQuery.php
+++ b/src/ORM/Connect/PDOQuery.php
@@ -2,9 +2,6 @@
 
 namespace SilverStripe\ORM\Connect;
 
-use ArrayIterator;
-use Iterator;
-
 /**
  * A result-set from a PDO database.
  */
@@ -17,7 +14,7 @@ class PDOQuery extends Query
 
     /**
      * Hook the result-set given into a Query class, suitable for use by SilverStripe.
-     * @param PDOStatementHandle $statement The internal PDOStatement containing the results
+     * @param PDOStatement $statement The internal PDOStatement containing the results
      */
     public function __construct(PDOStatementHandle $statement)
     {
@@ -29,13 +26,25 @@ public function __construct(PDOStatementHandle $statement)
         $statement->closeCursor();
     }
 
-    public function getIterator(): Iterator
+    public function seek($row)
     {
-        return new ArrayIterator($this->results);
+        $this->rowNum = $row - 1;
+        return $this->nextRecord();
     }
 
     public function numRecords()
     {
-        return count($this->results);
+        return count($this->results ?? []);
+    }
+
+    public function nextRecord()
+    {
+        $index = $this->rowNum + 1;
+
+        if (isset($this->results[$index])) {
+            return $this->results[$index];
+        } else {
+            return false;
+        }
     }
 }
diff --git a/src/ORM/Connect/Query.php b/src/ORM/Connect/Query.php
index 8aac231b2b5..af9e0c3a540 100644
--- a/src/ORM/Connect/Query.php
+++ b/src/ORM/Connect/Query.php
@@ -27,9 +27,30 @@
  * on providing the specific data-access methods that are required: {@link nextRecord()}, {@link numRecords()}
  * and {@link seek()}
  */
-abstract class Query implements \IteratorAggregate
+abstract class Query implements Iterator
 {
 
+    /**
+     * The current record in the iterator.
+     *
+     * @var array
+     */
+    protected $currentRecord = null;
+
+    /**
+     * The number of the current row in the iterator.
+     *
+     * @var int
+     */
+    protected $rowNum = -1;
+
+    /**
+     * Flag to keep track of whether iteration has begun, to prevent unnecessary seeks
+     *
+     * @var bool
+     */
+    protected $queryHasBegun = false;
+
     /**
      * Return an array containing all the values from a specific column. If no column is set, then the first will be
      * returned
@@ -41,7 +62,7 @@ public function column($column = null)
     {
         $result = [];
 
-        foreach ($this as $record) {
+        while ($record = $this->next()) {
             if ($column) {
                 $result[] = $record[$column];
             } else {
@@ -61,7 +82,6 @@ public function column($column = null)
     public function keyedColumn()
     {
         $column = [];
-
         foreach ($this as $record) {
             $val = $record[key($record)];
             $column[$val] = $val;
@@ -86,22 +106,13 @@ public function map()
     }
 
     /**
-     * Returns the first record in the result
+     * Returns the next record in the iterator.
      *
      * @return array
      */
     public function record()
     {
-        return $this->getIterator()->current();
-    }
-
-    /**
-     * @deprecated Use record() instead
-     * @return array
-     */
-    public function first()
-    {
-        return $this->record();
+        return $this->next();
     }
 
     /**
@@ -111,7 +122,7 @@ public function first()
      */
     public function value()
     {
-        $record = $this->record();
+        $record = $this->next();
         if ($record) {
             return $record[key($record)];
         }
@@ -153,10 +164,94 @@ public function table()
         return $result;
     }
 
+    /**
+     * Iterator function implementation. Rewind the iterator to the first item and return it.
+     * Makes use of {@link seek()} and {@link numRecords()}, takes care of the plumbing.
+     *
+     * @return void
+     */
+    #[\ReturnTypeWillChange]
+    public function rewind()
+    {
+        if ($this->queryHasBegun && $this->numRecords() > 0) {
+            $this->queryHasBegun = false;
+            $this->currentRecord = null;
+            $this->seek(0);
+        }
+    }
+
+    /**
+     * Iterator function implementation. Return the current item of the iterator.
+     *
+     * @return array
+     */
+    #[\ReturnTypeWillChange]
+    public function current()
+    {
+        if (!$this->currentRecord) {
+            return $this->next();
+        } else {
+            return $this->currentRecord;
+        }
+    }
+
+    /**
+     * Iterator function implementation. Return the first item of this iterator.
+     *
+     * @return array
+     */
+    public function first()
+    {
+        $this->rewind();
+        return $this->current();
+    }
+
+    /**
+     * Iterator function implementation. Return the row number of the current item.
+     *
+     * @return int
+     */
+    #[\ReturnTypeWillChange]
+    public function key()
+    {
+        return $this->rowNum;
+    }
+
+    /**
+     * Iterator function implementation. Return the next record in the iterator.
+     * Makes use of {@link nextRecord()}, takes care of the plumbing.
+     *
+     * @return array
+     */
+    #[\ReturnTypeWillChange]
+    public function next()
+    {
+        $this->queryHasBegun = true;
+        $this->currentRecord = $this->nextRecord();
+        $this->rowNum++;
+        return $this->currentRecord;
+    }
+
+    /**
+     * Iterator function implementation. Check if the iterator is pointing to a valid item.
+     *
+     * @return bool
+     */
+    #[\ReturnTypeWillChange]
+    public function valid()
+    {
+        if (!$this->queryHasBegun) {
+            $this->next();
+        }
+        return $this->currentRecord !== false;
+    }
+
     /**
      * Return the next record in the query result.
+     *
+     * @return array
      */
-    abstract public function getIterator(): Iterator;
+    abstract public function nextRecord();
 
     /**
      * Return the total number of items in the query result.
@@ -164,4 +259,12 @@ abstract public function getIterator(): Iterator;
      * @return int
      */
     abstract public function numRecords();
+
+    /**
+     * Go to a specific row number in the query result and return the record.
+     *
+     * @param int $rowNum Row number to go to.
+     * @return array
+     */
+    abstract public function seek($rowNum);
 }
diff --git a/src/ORM/DataList.php b/src/ORM/DataList.php
index 8dffc1dfe2b..72dfaf02ef2 100644
--- a/src/ORM/DataList.php
+++ b/src/ORM/DataList.php
@@ -6,12 +6,10 @@
 use SilverStripe\Dev\Debug;
 use SilverStripe\ORM\Filters\SearchFilter;
 use SilverStripe\ORM\Queries\SQLConditionGroup;
-use SilverStripe\View\TemplateIterator;
 use SilverStripe\View\ViewableData;
 use ArrayIterator;
 use Exception;
 use InvalidArgumentException;
-use Iterator;
 use LogicException;
 
 /**
@@ -51,13 +49,6 @@ class DataList extends ViewableData implements SS_List, Filterable, Sortable, Li
      */
     protected $dataQuery;
 
-    /**
-     * A cached Query to save repeated database calls. {@see DataList::getTemplateIteratorCount()}
-     *
-     * @var SilverStripe\ORM\Connect\Query
-     */
-    protected $finalisedQuery;
-
     /**
      * Create a new DataList.
      * No querying is done on construction, but the initial query schema is set up.
@@ -88,7 +79,6 @@ public function dataClass()
     public function __clone()
     {
         $this->dataQuery = clone $this->dataQuery;
-        $this->finalisedQuery = null;
     }
 
     /**
@@ -791,6 +781,20 @@ public function each($callback)
         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()
     {
         $val = "<h2>" . static::class . "</h2><ul>";
@@ -859,32 +863,13 @@ public function getQueryParams()
     /**
      * Returns an Iterator for this DataList.
      * This function allows you to use DataLists in foreach loops
-     */
-    public function getIterator(): Iterator
-    {
-        foreach ($this->getFinalisedQuery() as $row) {
-            yield $this->createDataObject($row);
-        }
-
-        // Re-set the finaliseQuery so that it can be re-executed
-        $this->finalisedQuery = null;
-    }
-
-    /**
-     * Returns the Query result for this DataList. Repeated calls will return
-     * a cached result, unless the DataQuery underlying this list has been
-     * modified
      *
-     * @return SilverStripe\ORM\Connect\Query
-     * @internal This API may change in minor releases
+     * @return ArrayIterator
      */
-    protected function getFinalisedQuery()
+    #[\ReturnTypeWillChange]
+    public function getIterator()
     {
-        if (!$this->finalisedQuery) {
-            $this->finalisedQuery = $this->dataQuery->query()->execute();
-        }
-
-        return $this->finalisedQuery;
+        return new ArrayIterator($this->toArray());
     }
 
     /**
@@ -895,10 +880,6 @@ protected function getFinalisedQuery()
     #[\ReturnTypeWillChange]
     public function count()
     {
-        if ($this->finalisedQuery) {
-            return $this->finalisedQuery->numRecords();
-        }
-
         return $this->dataQuery->count();
     }
 
@@ -1046,7 +1027,8 @@ public function byID($id)
      */
     public function column($colName = "ID")
     {
-        return $this->dataQuery->distinct(false)->column($colName);
+        $dataQuery = clone $this->dataQuery;
+        return $dataQuery->distinct(false)->column($colName);
     }
 
     /**
@@ -1192,7 +1174,7 @@ public function shuffle()
      */
     public function removeAll()
     {
-        foreach ($this as $item) {
+        foreach ($this->getGenerator() as $item) {
             $this->remove($item);
         }
         return $this;
@@ -1335,15 +1317,14 @@ public function chunkedFetch(int $chunkSize = 1000): iterable
         $currentChunk = 0;
 
         // Keep looping until we run out of chunks
-        while ($chunk = $this->limit($chunkSize, $chunkSize * $currentChunk)) {
+        while ($chunk = $this->limit($chunkSize, $chunkSize * $currentChunk)->getIterator()) {
             // Loop over all the item in our chunk
-            $count = 0;
             foreach ($chunk as $item) {
-                $count++;
                 yield $item;
             }
 
-            if ($count < $chunkSize) {
+
+            if ($chunk->count() < $chunkSize) {
                 // If our last chunk had less item than our chunkSize, we've reach the end.
                 break;
             }
diff --git a/src/ORM/ListDecorator.php b/src/ORM/ListDecorator.php
index f34e5ea5a91..d3f006e64b5 100644
--- a/src/ORM/ListDecorator.php
+++ b/src/ORM/ListDecorator.php
@@ -2,7 +2,6 @@
 
 namespace SilverStripe\ORM;
 
-use Iterator;
 use SilverStripe\View\ViewableData;
 use LogicException;
 
@@ -97,7 +96,8 @@ public function remove($itemObject)
         $this->list->remove($itemObject);
     }
 
-    public function getIterator(): Iterator
+    #[\ReturnTypeWillChange]
+    public function getIterator()
     {
         return $this->list->getIterator();
     }
diff --git a/src/ORM/ManyManyList.php b/src/ORM/ManyManyList.php
index ff841a9dc65..5ad69cd8f46 100644
--- a/src/ORM/ManyManyList.php
+++ b/src/ORM/ManyManyList.php
@@ -521,7 +521,7 @@ public function getExtraData($componentName, $itemID)
         $query->addWhere([
             "\"{$this->joinTable}\".\"{$this->localKey}\"" => $itemID
         ]);
-        $queryResult = $query->execute()->record();
+        $queryResult = $query->execute()->current();
         if ($queryResult) {
             foreach ($queryResult as $fieldName => $value) {
                 $result[$fieldName] = $value;
diff --git a/src/ORM/Map.php b/src/ORM/Map.php
index a29116c539b..6bcd68494db 100644
--- a/src/ORM/Map.php
+++ b/src/ORM/Map.php
@@ -4,7 +4,6 @@
 
 use ArrayAccess;
 use Countable;
-use Iterator;
 use IteratorAggregate;
 
 /**
@@ -251,55 +250,23 @@ public function offsetUnset($key)
     }
 
     /**
-     * Returns an Iterator for iterating over the complete set
+     * Returns an Map_Iterator instance for iterating over the complete set
      * of items in the map.
      *
-     * Satisfies the IteratorAggregate interface.
-     */
-    public function getIterator(): Iterator
-    {
-        $keyField = $this->keyField;
-        $valueField = $this->valueField;
-
-        foreach ($this->firstItems as $k => $v) {
-            yield $k => $v;
-        }
-
-        foreach ($this->list as $record) {
-            if (isset($this->firstItems[$record->$keyField])) {
-                continue;
-            }
-            if (isset($this->lastItems[$record->$keyField])) {
-                continue;
-            }
-            yield $this->extractValue($record, $this->keyField) => $this->extractValue($record, $this->valueField);
-        }
-
-        foreach ($this->lastItems as $k => $v) {
-            yield $k => $v;
-        }
-    }
-
-    /**
-     * Extracts a value from an item in the list, where the item is either an
-     * object or array.
+     * Satisfies the IteratorAggreagte interface.
      *
-     * @param  array|object $item
-     * @param  string $key
-     * @return mixed
+     * @return Map_Iterator
      */
-    protected function extractValue($item, $key)
+    #[\ReturnTypeWillChange]
+    public function getIterator()
     {
-        if (is_object($item)) {
-            if (method_exists($item, 'hasMethod') && $item->hasMethod($key)) {
-                return $item->{$key}();
-            }
-            return $item->{$key};
-        } else {
-            if (array_key_exists($key, $item)) {
-                return $item[$key];
-            }
-        }
+        return new Map_Iterator(
+            $this->list->getIterator(),
+            $this->keyField,
+            $this->valueField,
+            $this->firstItems,
+            $this->lastItems
+        );
     }
 
     /**
diff --git a/src/ORM/Map_Iterator.php b/src/ORM/Map_Iterator.php
new file mode 100644
index 00000000000..d645ca07df8
--- /dev/null
+++ b/src/ORM/Map_Iterator.php
@@ -0,0 +1,200 @@
+<?php
+
+namespace SilverStripe\ORM;
+
+use Iterator;
+
+/**
+ * Builds a map iterator around an Iterator.  Called by Map
+ */
+class Map_Iterator implements Iterator
+{
+
+    /**
+     * @var Iterator
+     **/
+    protected $items;
+
+    protected $keyField, $titleField;
+
+    protected $firstItemIdx = 0;
+
+    protected $endItemIdx;
+
+    protected $firstItems = [];
+    protected $lastItems = [];
+
+    protected $excludedItems = [];
+
+    /**
+     * @param Iterator $items The iterator to build this map from
+     * @param string $keyField The field to use for the keys
+     * @param string $titleField The field to use for the values
+     * @param array $firstItems An optional map of items to show first
+     * @param array $lastItems An optional map of items to show last
+     */
+    public function __construct(Iterator $items, $keyField, $titleField, $firstItems = null, $lastItems = null)
+    {
+        $this->items = $items;
+        $this->keyField = $keyField;
+        $this->titleField = $titleField;
+        $this->endItemIdx = null;
+
+        if ($firstItems) {
+            foreach ($firstItems as $k => $v) {
+                $this->firstItems[] = [$k, $v];
+                $this->excludedItems[] = $k;
+            }
+        }
+
+        if ($lastItems) {
+            foreach ($lastItems as $k => $v) {
+                $this->lastItems[] = [$k, $v];
+                $this->excludedItems[] = $k;
+            }
+        }
+    }
+
+    /**
+     * Rewind the Iterator to the first element.
+     *
+     * @return mixed
+     */
+    #[\ReturnTypeWillChange]
+    public function rewind()
+    {
+        $this->firstItemIdx = 0;
+        $this->endItemIdx = null;
+
+        $rewoundItem = $this->items->rewind();
+
+        if (isset($this->firstItems[$this->firstItemIdx])) {
+            return $this->firstItems[$this->firstItemIdx][1];
+        } else {
+            if ($rewoundItem) {
+                return $this->extractValue($rewoundItem, $this->titleField);
+            } else {
+                if (!$this->items->valid() && $this->lastItems) {
+                    $this->endItemIdx = 0;
+
+                    return $this->lastItems[0][1];
+                }
+            }
+        }
+    }
+
+    /**
+     * Return the current element.
+     *
+     * @return mixed
+     */
+    #[\ReturnTypeWillChange]
+    public function current()
+    {
+        if (($this->endItemIdx !== null) && isset($this->lastItems[$this->endItemIdx])) {
+            return $this->lastItems[$this->endItemIdx][1];
+        } else {
+            if (isset($this->firstItems[$this->firstItemIdx])) {
+                return $this->firstItems[$this->firstItemIdx][1];
+            }
+        }
+        return $this->extractValue($this->items->current(), $this->titleField);
+    }
+
+    /**
+     * Extracts a value from an item in the list, where the item is either an
+     * object or array.
+     *
+     * @param  array|object $item
+     * @param  string $key
+     * @return mixed
+     */
+    protected function extractValue($item, $key)
+    {
+        if (is_object($item)) {
+            if (method_exists($item, 'hasMethod') && $item->hasMethod($key)) {
+                return $item->{$key}();
+            }
+            return $item->{$key};
+        } else {
+            if (array_key_exists($key, $item ?? [])) {
+                return $item[$key];
+            }
+        }
+    }
+
+    /**
+     * Return the key of the current element.
+     *
+     * @return string
+     */
+    #[\ReturnTypeWillChange]
+    public function key()
+    {
+        if (($this->endItemIdx !== null) && isset($this->lastItems[$this->endItemIdx])) {
+            return $this->lastItems[$this->endItemIdx][0];
+        } else {
+            if (isset($this->firstItems[$this->firstItemIdx])) {
+                return $this->firstItems[$this->firstItemIdx][0];
+            } else {
+                return $this->extractValue($this->items->current(), $this->keyField);
+            }
+        }
+    }
+
+    /**
+     * Move forward to next element.
+     *
+     * @return mixed
+     */
+    #[\ReturnTypeWillChange]
+    public function next()
+    {
+        $this->firstItemIdx++;
+
+        if (isset($this->firstItems[$this->firstItemIdx])) {
+            return $this->firstItems[$this->firstItemIdx][1];
+        } else {
+            if (!isset($this->firstItems[$this->firstItemIdx - 1])) {
+                $this->items->next();
+            }
+
+            if ($this->excludedItems) {
+                while (($c = $this->items->current()) && in_array($c->{$this->keyField}, $this->excludedItems ?? [], true)) {
+                    $this->items->next();
+                }
+            }
+        }
+
+        if (!$this->items->valid()) {
+            // iterator has passed the preface items, off the end of the items
+            // list. Track through the end items to go through to the next
+            if ($this->endItemIdx === null) {
+                $this->endItemIdx = -1;
+            }
+
+            $this->endItemIdx++;
+
+            if (isset($this->lastItems[$this->endItemIdx])) {
+                return $this->lastItems[$this->endItemIdx];
+            }
+
+            return false;
+        }
+    }
+
+    /**
+     * Checks if current position is valid.
+     *
+     * @return boolean
+     */
+    #[\ReturnTypeWillChange]
+    public function valid()
+    {
+        return (
+            (isset($this->firstItems[$this->firstItemIdx])) ||
+            (($this->endItemIdx !== null) && isset($this->lastItems[$this->endItemIdx])) ||
+            $this->items->valid()
+        );
+    }
+}
diff --git a/src/ORM/PaginatedList.php b/src/ORM/PaginatedList.php
index b962c0e546a..f7289e9a8bd 100644
--- a/src/ORM/PaginatedList.php
+++ b/src/ORM/PaginatedList.php
@@ -8,7 +8,6 @@
 use SilverStripe\View\ArrayData;
 use ArrayAccess;
 use Exception;
-use Iterator;
 use IteratorIterator;
 
 /**
@@ -209,7 +208,11 @@ public function setLimitItems($limit)
         return $this;
     }
 
-    public function getIterator(): Iterator
+    /**
+     * @return IteratorIterator
+     */
+    #[\ReturnTypeWillChange]
+    public function getIterator()
     {
         $pageLength = $this->getPageLength();
         if ($this->limitItems && $pageLength) {
@@ -222,21 +225,6 @@ public function getIterator(): Iterator
         }
     }
 
-    /**
-     * @return array
-     */
-    public function toArray()
-    {
-        $result = [];
-
-        // Use getIterator()
-        foreach ($this as $record) {
-            $result[] = $record;
-        }
-
-        return $result;
-    }
-
     /**
      * Returns a set of links to all the pages in the list. This is useful for
      * basic pagination.
@@ -356,8 +344,8 @@ public function PaginationSummary($context = 4)
             $num = $i + 1;
 
             $emptyRange = $num != 1 && $num != $total && (
-                    $num == $left - 1 || $num == $right + 1
-                );
+                $num == $left - 1 || $num == $right + 1
+            );
 
             if ($emptyRange) {
                 $result->push(new ArrayData([
diff --git a/src/ORM/UnsavedRelationList.php b/src/ORM/UnsavedRelationList.php
index 0206ef19edb..51cde920fd9 100644
--- a/src/ORM/UnsavedRelationList.php
+++ b/src/ORM/UnsavedRelationList.php
@@ -4,7 +4,6 @@
 
 use InvalidArgumentException;
 use ArrayIterator;
-use Iterator;
 use SilverStripe\ORM\FieldType\DBField;
 
 /**
@@ -121,8 +120,11 @@ public function dataClass()
 
     /**
      * Returns an Iterator for this relation.
+     *
+     * @return ArrayIterator
      */
-    public function getIterator(): Iterator
+    #[\ReturnTypeWillChange]
+    public function getIterator()
     {
         return new ArrayIterator($this->toArray());
     }
diff --git a/src/View/SSViewer_Scope.php b/src/View/SSViewer_Scope.php
index 28d1b541f0d..224fd07530a 100644
--- a/src/View/SSViewer_Scope.php
+++ b/src/View/SSViewer_Scope.php
@@ -3,7 +3,6 @@
 namespace SilverStripe\View;
 
 use ArrayIterator;
-use Countable;
 use Iterator;
 
 /**
@@ -290,31 +289,16 @@ public function next()
         }
 
         if (!$this->itemIterator) {
-            // Note: it is important that getIterator() is called before count() as implemenations may rely on
-            // this to efficiency get both the number of records and an iterator (e.g. DataList does this)
-
-            // Item may be an array or a regular IteratorAggregate
             if (is_array($this->item)) {
                 $this->itemIterator = new ArrayIterator($this->item);
             } else {
                 $this->itemIterator = $this->item->getIterator();
-
-                // This will execute code in a generator up to the first yield. For example, this ensures that
-                // DataList::getIterator() is called before Datalist::count()
-                $this->itemIterator->rewind();
-            }
-
-            // If the item implements Countable, use that to fetch the count, otherwise we have to inspect the
-            // iterator and then rewind it.
-            if ($this->item instanceof Countable) {
-                $this->itemIteratorTotal = count($this->item);
-            } else {
-                $this->itemIteratorTotal = iterator_count($this->itemIterator);
-                $this->itemIterator->rewind();
             }
 
             $this->itemStack[$this->localIndex][SSViewer_Scope::ITEM_ITERATOR] = $this->itemIterator;
+            $this->itemIteratorTotal = iterator_count($this->itemIterator); // Count the total number of items
             $this->itemStack[$this->localIndex][SSViewer_Scope::ITEM_ITERATOR_TOTAL] = $this->itemIteratorTotal;
+            $this->itemIterator->rewind();
         } else {
             $this->itemIterator->next();
         }
diff --git a/src/View/ViewableData.php b/src/View/ViewableData.php
index 4fd3051c206..2755b1da4a8 100644
--- a/src/View/ViewableData.php
+++ b/src/View/ViewableData.php
@@ -5,7 +5,6 @@
 use ArrayIterator;
 use Exception;
 use InvalidArgumentException;
-use Iterator;
 use IteratorAggregate;
 use LogicException;
 use SilverStripe\Core\ClassInfo;
@@ -574,8 +573,11 @@ public function getXMLValues($fields)
      *
      * This is useful so you can use a single record inside a <% control %> block in a template - and then use
      * to access individual fields on this object.
+     *
+     * @return ArrayIterator
      */
-    public function getIterator(): Iterator
+    #[\ReturnTypeWillChange]
+    public function getIterator()
     {
         return new ArrayIterator([$this]);
     }
diff --git a/tests/php/ORM/DatabaseTest.php b/tests/php/ORM/DatabaseTest.php
index 33a45caaf38..25fa3deed8e 100644
--- a/tests/php/ORM/DatabaseTest.php
+++ b/tests/php/ORM/DatabaseTest.php
@@ -74,7 +74,7 @@ public function testMySQLCreateTableOptions()
                 'SHOW TABLE STATUS WHERE "Name" = \'%s\'',
                 'DatabaseTest_MyObject'
             )
-        )->record();
+        )->first();
         $this->assertEquals(
             $ret['Engine'],
             'InnoDB',
diff --git a/tests/php/ORM/ListDecoratorTest.php b/tests/php/ORM/ListDecoratorTest.php
index 0410bba7653..2e85f50c970 100644
--- a/tests/php/ORM/ListDecoratorTest.php
+++ b/tests/php/ORM/ListDecoratorTest.php
@@ -2,7 +2,6 @@
 
 namespace SilverStripe\ORM\Tests;
 
-use ArrayIterator;
 use LogicException;
 use PHPUnit\Framework\MockObject\MockObject;
 use SilverStripe\Dev\SapphireTest;
@@ -35,9 +34,8 @@ protected function setUp(): void
 
     public function testGetIterator()
     {
-        $iterator = new ArrayIterator();
-        $this->list->expects($this->once())->method('getIterator')->willReturn($iterator);
-        $this->assertSame($iterator, $this->decorator->getIterator());
+        $this->list->expects($this->once())->method('getIterator')->willReturn('mock');
+        $this->assertSame('mock', $this->decorator->getIterator());
     }
 
     public function testCanSortBy()
diff --git a/tests/php/ORM/MySQLDatabaseTest.php b/tests/php/ORM/MySQLDatabaseTest.php
index e4ffdfd2fd6..7b084b04522 100644
--- a/tests/php/ORM/MySQLDatabaseTest.php
+++ b/tests/php/ORM/MySQLDatabaseTest.php
@@ -45,47 +45,58 @@ public function testPreparedStatements()
         $this->assertInstanceOf(MySQLQuery::class, $result3);
 
         // Iterating one level should not buffer, but return the right result
-        $result1Array = [];
-        foreach ($result1 as $record) {
-            $result1Array[] = $record;
-        }
         $this->assertEquals(
             [
-                [ 'Sort' => 1, 'Title' => 'First Item' ],
-                [ 'Sort' => 2, 'Title' => 'Second Item' ],
-                [ 'Sort' => 3, 'Title' => 'Third Item' ],
-                [ 'Sort' => 4, 'Title' => 'Last Item' ],
+                'Sort' => 1,
+                'Title' => 'First Item'
+            ],
+            $result1->next()
+        );
+        $this->assertEquals(
+            [
+                'Sort' => 2,
+                'Title' => 'Second Item'
             ],
-            $result1Array
+            $result1->next()
+        );
+
+        // Test first
+        $this->assertEquals(
+            [
+                'Sort' => 1,
+                'Title' => 'First Item'
+            ],
+            $result1->first()
+        );
+
+        // Test seek
+        $this->assertEquals(
+            [
+                'Sort' => 2,
+                'Title' => 'Second Item'
+            ],
+            $result1->seek(1)
         );
 
         // Test count
         $this->assertEquals(4, $result1->numRecords());
 
         // Test second statement
-        $result2Array = [];
-        foreach ($result2 as $record) {
-            $result2Array[] = $record;
-            break;
-        }
         $this->assertEquals(
             [
-                [ 'Sort' => 3, 'Title' => 'Third Item' ],
+                'Sort' => 3,
+                'Title' => 'Third Item'
             ],
-            $result2Array
+            $result2->next()
         );
 
         // Test non-prepared query
-        $result3Array = [];
-        foreach ($result3 as $record) {
-            $result3Array[] = $record;
-            break;
-        }
         $this->assertEquals(
             [
-                [ 'Sort' => 1, 'Title' => 'First Item' ],
+                'Sort' => 1,
+                'Title' => 'First Item'
             ],
-            $result3Array
+            $result3->next()
         );
     }
 
diff --git a/tests/php/ORM/PDODatabaseTest.php b/tests/php/ORM/PDODatabaseTest.php
index 5462056711a..fa91676c536 100644
--- a/tests/php/ORM/PDODatabaseTest.php
+++ b/tests/php/ORM/PDODatabaseTest.php
@@ -43,47 +43,58 @@ public function testPreparedStatements()
         $this->assertInstanceOf(PDOQuery::class, $result3);
 
         // Iterating one level should not buffer, but return the right result
-        $result1Array = [];
-        foreach ($result1 as $record) {
-            $result1Array[] = $record;
-        }
         $this->assertEquals(
             [
-                [ 'Sort' => 1, 'Title' => 'First Item' ],
-                [ 'Sort' => 2, 'Title' => 'Second Item' ],
-                [ 'Sort' => 3, 'Title' => 'Third Item' ],
-                [ 'Sort' => 4, 'Title' => 'Last Item' ],
+                'Sort' => 1,
+                'Title' => 'First Item'
+            ],
+            $result1->next()
+        );
+        $this->assertEquals(
+            [
+                'Sort' => 2,
+                'Title' => 'Second Item'
             ],
-            $result1Array
+            $result1->next()
+        );
+
+        // Test first
+        $this->assertEquals(
+            [
+                'Sort' => 1,
+                'Title' => 'First Item'
+            ],
+            $result1->first()
+        );
+
+        // Test seek
+        $this->assertEquals(
+            [
+                'Sort' => 2,
+                'Title' => 'Second Item'
+            ],
+            $result1->seek(1)
         );
 
         // Test count
         $this->assertEquals(4, $result1->numRecords());
 
         // Test second statement
-        $result2Array = [];
-        foreach ($result2 as $record) {
-            $result2Array[] = $record;
-            break;
-        }
         $this->assertEquals(
             [
-                [ 'Sort' => 3, 'Title' => 'Third Item' ],
+                'Sort' => 3,
+                'Title' => 'Third Item'
             ],
-            $result2Array
+            $result2->next()
         );
 
         // Test non-prepared query
-        $result3Array = [];
-        foreach ($result3 as $record) {
-            $result3Array[] = $record;
-            break;
-        }
         $this->assertEquals(
             [
-                [ 'Sort' => 1, 'Title' => 'First Item' ],
+                'Sort' => 1,
+                'Title' => 'First Item'
             ],
-            $result3Array
+            $result3->next()
         );
     }
 
diff --git a/tests/php/ORM/PaginatedListTest.php b/tests/php/ORM/PaginatedListTest.php
index f8a1e2c9772..fb63403d6ec 100644
--- a/tests/php/ORM/PaginatedListTest.php
+++ b/tests/php/ORM/PaginatedListTest.php
@@ -90,7 +90,7 @@ public function testSetCurrentPage()
         $this->assertEquals(1, $list->CurrentPage());
     }
 
-    public function testIteration()
+    public function testGetIterator()
     {
         $list = new PaginatedList(
             new ArrayList([
@@ -105,23 +105,26 @@ public function testIteration()
 
         $this->assertListEquals(
             [['Num' => 1], ['Num' => 2]],
-            $list
+            ArrayList::create($list->getIterator()->getInnerIterator()->getArrayCopy())
         );
 
         $list->setCurrentPage(2);
         $this->assertListEquals(
             [['Num' => 3], ['Num' => 4]],
-            $list
+            ArrayList::create($list->getIterator()->getInnerIterator()->getArrayCopy())
         );
 
         $list->setCurrentPage(3);
         $this->assertListEquals(
             [['Num' => 5]],
-            $list
+            ArrayList::create($list->getIterator()->getInnerIterator()->getArrayCopy())
         );
 
         $list->setCurrentPage(999);
-        $this->assertListEquals([], $list);
+        $this->assertListEquals(
+            [],
+            ArrayList::create($list->getIterator()->getInnerIterator()->getArrayCopy())
+        );
 
         // Test disabled paging
         $list->setPageLength(0);
@@ -134,13 +137,14 @@ public function testIteration()
                 ['Num' => 4],
                 ['Num' => 5],
             ],
-            $list
+            ArrayList::create($list->getIterator()->getInnerIterator()->getArrayCopy())
         );
 
         // Test with dataobjectset
         $players = Player::get();
         $list = new PaginatedList($players);
         $list->setPageLength(1);
+        $list->getIterator();
         $this->assertEquals(
             4,
             $list->getTotalItems(),
@@ -219,10 +223,10 @@ public function testLimitItems()
         $list = new PaginatedList($list);
 
         $list->setCurrentPage(3);
-        $this->assertEquals(10, count($list->toArray()));
+        $this->assertCount(10, $list->getIterator()->getInnerIterator());
 
         $list->setLimitItems(false);
-        $this->assertEquals(50, count($list->toArray()));
+        $this->assertCount(50, $list->getIterator()->getInnerIterator());
     }
 
     public function testCurrentPage()