add migration that removes column ex_termine.topic_id, fixes #1224

Closes #1224

Merge request studip/studip!735

db/migrations/20220629_remove_column_ex_termine_topic_id.php

+<?php
+/**
+ * @see https://gitlab.studip.de/studip/studip/-/issues/1224
+ * @see https://gitlab.studip.de/studip/studip/-/issues/881
+ */
+final class RemoveColumnExTermineTopicId extends Migration
+{
+    public function description()
+    {
+        return 'Removes unused column topic_id from table ex_termine.';
+    }
+
+    protected function up()
+    {
+        if (!$this->columnExists('ex_termine', 'topic_id')) {
+            $this->write("Column ex_termine.topic_id does not exist");
+            return;
+        }
+
+        $query = "ALTER TABLE `ex_termine`
+                  DROP COLUMN `topic_id`";
+        DBManager::get()->exec($query);
+    }
+
+    protected function down()
+    {
+        if ($this->columnExists('ex_termine', 'topic_id')) {
+            $this->write("Column ex_termine.topic_id already exists");
+            return;
+        }
+
+        $query = "ALTER TABLE `ex_termine`
+                  ADD COLUMN `topic_id` VARCHAR(32) COLLATE latin1_bin DEFAULT NULL";
+        DBManager::get()->exec($query);
+    }
+
+    protected function columnExists(string $table, string $column): bool
+    {
+        $query = "SHOW COLUMNS FROM `{$table}` LIKE ?";
+        return (bool) DBManager::get()->fetchOne($query, [$column]);
+    }
+}