From 9a3532265f89289659bb42c4c3e37d84dbf2b0a4 Mon Sep 17 00:00:00 2001
From: Johann Hoffmann <ma0646@technikum-wien.at>
Date: Thu, 10 Sep 2026 11:50:51 +0200
Subject: [PATCH] information schema guard check for the data migration & table
 alter statements aswell, so they dont run on every checksystem.php invocation

---
 .../75469_le_optional_4_projektarbeit.php     | 58 ++++++++++++-------
 1 file changed, 38 insertions(+), 20 deletions(-)

diff --git a/system/dbupdate_3.4/75469_le_optional_4_projektarbeit.php b/system/dbupdate_3.4/75469_le_optional_4_projektarbeit.php
index fe4a8e117..71b45da06 100644
--- a/system/dbupdate_3.4/75469_le_optional_4_projektarbeit.php
+++ b/system/dbupdate_3.4/75469_le_optional_4_projektarbeit.php
@@ -22,31 +22,49 @@ foreach ($cols_to_add as $col => $type) {
 	}
 }
 
-// retrieve lehrveranstaltung_id & studiensemester_kurzbz from tbl_lehreinheit
-// into new columns based on the existing reference
-$migration_qry = "UPDATE lehre.tbl_projektarbeit p
-                  SET lehrveranstaltung_id = l.lehrveranstaltung_id,
-                      studiensemester_kurzbz = l.studiensemester_kurzbz
-                  FROM lehre.tbl_lehreinheit l
-                  WHERE p.lehreinheit_id = l.lehreinheit_id
-                  AND (p.lehrveranstaltung_id IS NULL OR p.studiensemester_kurzbz IS NULL);";
+// run the data migration and the constraint change only once.
+// Target state: lehrveranstaltung_id NOT NULL, studiensemester_kurzbz NOT NULL, lehreinheit_id NULLable.
+// The check returns a row as long as one of the three columns is not in the target state.
+$state_check = "SELECT 1 FROM information_schema.columns
+                WHERE table_schema = 'lehre' AND table_name = 'tbl_projektarbeit'
+                AND ((column_name IN ('lehrveranstaltung_id', 'studiensemester_kurzbz') AND is_nullable = 'YES')
+                     OR (column_name = 'lehreinheit_id' AND is_nullable = 'NO'))";
 
-if ($db->db_query($migration_qry)) {
-	echo "<br>Datenmigration von lehreinheit_id zu lehrveranstaltung_id & studiensemester_kurzbz abgeschlossen.";
+$migration_pending = false;
+
+if ($result = $db->db_query($state_check)) {
+	$migration_pending = ($db->db_num_rows($result) > 0);
 } else {
-	echo "<strong>Migration Error: ".$db->db_last_error()."</strong><br>";
+	echo "<strong>State Check Error: ".$db->db_last_error()."</strong><br>";
 }
 
-// set NOT NULL and make lehreinheit_id NULLable
-$constraint_qry = "ALTER TABLE lehre.tbl_projektarbeit 
-                   ALTER COLUMN lehrveranstaltung_id SET NOT NULL,
-                   ALTER COLUMN studiensemester_kurzbz SET NOT NULL,
-                   ALTER COLUMN lehreinheit_id DROP NOT NULL;";
+if ($migration_pending) {
+	// retrieve lehrveranstaltung_id & studiensemester_kurzbz from tbl_lehreinheit
+	// into new columns based on the existing reference
+	$migration_qry = "UPDATE lehre.tbl_projektarbeit p
+	                  SET lehrveranstaltung_id = l.lehrveranstaltung_id,
+	                      studiensemester_kurzbz = l.studiensemester_kurzbz
+	                  FROM lehre.tbl_lehreinheit l
+	                  WHERE p.lehreinheit_id = l.lehreinheit_id
+	                  AND (p.lehrveranstaltung_id IS NULL OR p.studiensemester_kurzbz IS NULL);";
 
-if ($db->db_query($constraint_qry)) {
-	echo "<br>Constraints updated lehrveranstaltung_id SET NOT NULL, studiensemester_kurzbz SET NOT NULL, lehreinheit_id DROP NOT NULL.";
-} else {
-	echo "<strong>Alter Constraints Error: ".$db->db_last_error()."</strong><br>";
+	if ($db->db_query($migration_qry)) {
+		echo "<br>Datenmigration von lehreinheit_id zu lehrveranstaltung_id & studiensemester_kurzbz abgeschlossen.";
+	} else {
+		echo "<strong>Migration Error: ".$db->db_last_error()."</strong><br>";
+	}
+
+	// set NOT NULL and make lehreinheit_id NULLable
+	$constraint_qry = "ALTER TABLE lehre.tbl_projektarbeit
+	                   ALTER COLUMN lehrveranstaltung_id SET NOT NULL,
+	                   ALTER COLUMN studiensemester_kurzbz SET NOT NULL,
+	                   ALTER COLUMN lehreinheit_id DROP NOT NULL;";
+
+	if ($db->db_query($constraint_qry)) {
+		echo "<br>Constraints updated lehrveranstaltung_id SET NOT NULL, studiensemester_kurzbz SET NOT NULL, lehreinheit_id DROP NOT NULL.";
+	} else {
+		echo "<strong>Alter Constraints Error: ".$db->db_last_error()."</strong><br>";
+	}
 }
 
 // add fkey for lehrveranstaltung_id