diff --git a/core/attributedef/AttributeObjectKey.php b/core/attributedef/AttributeObjectKey.php
new file mode 100644
index 0000000000..356eee24ed
--- /dev/null
+++ b/core/attributedef/AttributeObjectKey.php
@@ -0,0 +1,107 @@
+<?php
+
+/**
+ * An external key for which the class is defined as the value of another attribute
+ *
+ * @package     iTopORM
+ */
+class AttributeObjectKey extends AttributeDBFieldVoid
+{
+    const SEARCH_WIDGET_TYPE = self::SEARCH_WIDGET_TYPE_EXTERNAL_KEY;
+
+    /**
+     * Useless constructor, but if not present PHP 7.4.0/7.4.1 is crashing :( (N°2329)
+     *
+     * @see https://www.php.net/manual/fr/language.oop5.decon.php states that child constructor can be ommited
+     * @see https://bugs.php.net/bug.php?id=79010 bug solved in PHP 7.4.9
+     *
+     * @param string $sCode
+     * @param array $aParams
+     *
+     * @throws \Exception
+     * @noinspection SenselessProxyMethodInspection
+     */
+    public function __construct($sCode, $aParams)
+    {
+        parent::__construct($sCode, $aParams);
+    }
+
+    public static function ListExpectedParams()
+    {
+        return array_merge(parent::ListExpectedParams(), array('class_attcode', 'is_null_allowed'));
+    }
+
+    public function GetEditClass()
+    {
+        return "String";
+    }
+
+    protected function GetSQLCol($bFullSpec = false)
+    {
+        return "INT(11)" . ($bFullSpec ? " DEFAULT 0" : "");
+    }
+
+    public function GetDefaultValue(DBObject $oHostObject = null)
+    {
+        return 0;
+    }
+
+    public function IsNullAllowed()
+    {
+        return $this->Get("is_null_allowed");
+    }
+
+
+    public function GetBasicFilterOperators()
+    {
+        return parent::GetBasicFilterOperators();
+    }
+
+    public function GetBasicFilterLooseOperator()
+    {
+        return parent::GetBasicFilterLooseOperator();
+    }
+
+    public function GetBasicFilterSQLExpr($sOpCode, $value)
+    {
+        return parent::GetBasicFilterSQLExpr($sOpCode, $value);
+    }
+
+    public function GetNullValue()
+    {
+        return 0;
+    }
+
+    public function IsNull($proposedValue)
+    {
+        return ($proposedValue == 0);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function HasAValue($proposedValue): bool
+    {
+        return ((int)$proposedValue) !== 0;
+    }
+
+    /**
+     * @inheritDoc
+     *
+     * @param int|DBObject $proposedValue Object key or valid ({@see MetaModel::IsValidObject()}) datamodel object
+     */
+    public function MakeRealValue($proposedValue, $oHostObj)
+    {
+        if (is_null($proposedValue)) {
+            return 0;
+        }
+        if ($proposedValue === '') {
+            return 0;
+        }
+        if (MetaModel::IsValidObject($proposedValue)) {
+            return $proposedValue->GetKey();
+        }
+
+        return (int)$proposedValue;
+    }
+}
\ No newline at end of file