Cache foreign key display values

Avoid repeated sql queries for foreighn keys, speed things up
when duplicate key values are in the result set to display.

Signed-off-by: Maximilian Krög <maxi_kroeg@web.de>

Author: MoonE

libraries/classes/Display/Results.php

@@ -35,6 +35,7 @@
 use function __;
 use function _pgettext;
 use function array_filter;
+use function array_key_exists;
 use function array_keys;
 use function array_merge;
 use function array_shift;
@@ -249,6 +250,9 @@ class Results
     /** @var Template */
     public $template;
 
+    /** @var array<string, string|null> */
+    private $foreignKeyDisplayCache = [];
+
     /**
      * @param string $db       the database name
      * @param string $table    the table name
@@ -4363,22 +4367,25 @@ private function handleNonPrintableContents(
      */
     private function getFromForeign(array $fieldInfo, string $whereComparison): ?string
     {
+        $key = json_encode([$fieldInfo[0], $fieldInfo[1], $fieldInfo[2], $fieldInfo[3], $whereComparison]);
+        if (array_key_exists($key, $this->foreignKeyDisplayCache)) {
+            return $this->foreignKeyDisplayCache[$key];
+        }
+
         $dispsql = 'SELECT ' . Util::backquote($fieldInfo[2])
             . ' FROM ' . Util::backquote($fieldInfo[3]) . '.' . Util::backquote($fieldInfo[0])
             . ' WHERE ' . Util::backquote($fieldInfo[1]) . $whereComparison
             . ' LIMIT 1';
 
         $dispval = $this->dbi->fetchValue($dispsql);
         if ($dispval === false) {
-            return __('Link not found!');
-        }
-
-        if ($dispval === null) {
-            return null;
+            $dispval = __('Link not found!');
+        } elseif ($dispval !== null) {
+            // Truncate values that are too long, see: #17902
+            [, $dispval] = $this->getPartialText($dispval);
         }
 
-        // Truncate values that are too long, see: #17902
-        [, $dispval] = $this->getPartialText($dispval);
+        $this->foreignKeyDisplayCache[$key] = $dispval;
 
         return $dispval;
     }