recreates foreign-keys, changes delete rules.

Checked all remaining foreign keys using:
```
SELECT
    rc.DELETE_RULE, rc.UPDATE_RULE,
    kcu.TABLE_NAME, kcu.COLUMN_NAME, kcu.CONSTRAINT_NAME, kcu.REFERENCED_TABLE_NAME, kcu.REFERENCED_COLUMN_NAME
FROM
  INFORMATION_SCHEMA.KEY_COLUMN_USAGE kcu
INNER JOIN information_schema.REFERENTIAL_CONSTRAINTS AS rc ON kcu.CONSTRAINT_NAME = rc.CONSTRAINT_NAME
WHERE
  kcu.REFERENCED_TABLE_SCHEMA = 'domjudge'
  AND DELETE_RULE = 'RESTRICT';
```

After some discussion with Jaap it was decided to set columns referring
to judgedaemons to null instead of cascading the delete. A single
foreign key's delete rule is kept as 'restrict' since that case looks to
be sensible.

Fixes #2464, #2465.

Author: tuupke

webapp/migrations/Version20240825115643.php

@@ -0,0 +1,64 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Auto-generated Migration: Please modify to your needs!
+ */
+final class Version20240825115643 extends AbstractMigration
+{
+    // All remaining foreign keys are now cascade.
+    // There is one exception: immutable_executable.immutable_execid is still referenced and removal is restricted.
+    public function getDescription(): string
+    {
+        return 'Recreate \'restrict foreign key constraints\', cascading or setting to null where needed.';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->dropKeys();
+        $this->addKeys(true);
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->dropKeys();
+
+        // Reinstate the 'restrict' keys.
+        $this->addKeys(false);
+    }
+
+    public function dropKeys(): void
+    {
+        $this->addSql('ALTER TABLE debug_package DROP CONSTRAINT FK_9E17399BE0E4FC3E');
+        $this->addSql('ALTER TABLE version DROP CONSTRAINT FK_BF1CD3C32271845');
+        $this->addSql('ALTER TABLE version DROP CONSTRAINT FK_BF1CD3C3E0E4FC3E');
+        $this->addSql('ALTER TABLE judging_run DROP CONSTRAINT FK_29A6E6E13CBA64F2');
+        $this->addSql('ALTER TABLE judging_run DROP CONSTRAINT judging_run_ibfk_1');
+        $this->addSql('ALTER TABLE judgetask DROP CONSTRAINT judgetask_ibfk_1');
+    }
+
+    public function addKeys(bool $suffix): void
+    {
+        // foreign-keys that are related to judgehosts are set to null so that no data is lost.
+        $cascadeClause = $suffix ? 'ON DELETE CASCADE' : '';
+        $nullClause = $suffix ? 'ON DELETE SET NULL' : '';
+
+        $this->addSql('ALTER TABLE version ADD CONSTRAINT `FK_BF1CD3C32271845` FOREIGN KEY (`langid`) REFERENCES `language` (`langid`) ' . $cascadeClause);
+        $this->addSql('ALTER TABLE version ADD CONSTRAINT `FK_BF1CD3C3E0E4FC3E` FOREIGN KEY (`judgehostid`) REFERENCES `judgehost` (`judgehostid`) ' . $nullClause);
+        $this->addSql('ALTER TABLE judging_run ADD CONSTRAINT `FK_29A6E6E13CBA64F2` FOREIGN KEY (`judgetaskid`) REFERENCES `judgetask` (`judgetaskid`) ' . $cascadeClause);
+        $this->addSql('ALTER TABLE judging_run ADD CONSTRAINT `judging_run_ibfk_1` FOREIGN KEY (`testcaseid`) REFERENCES `testcase` (`testcaseid`) ' . $cascadeClause);
+        $this->addSql('ALTER TABLE judgetask ADD CONSTRAINT `judgetask_ibfk_1` FOREIGN KEY (`judgehostid`) REFERENCES `judgehost` (`judgehostid`) ' . $nullClause);
+        $this->addSql('ALTER TABLE debug_package ADD CONSTRAINT `FK_9E17399BE0E4FC3E` FOREIGN KEY (`judgehostid`) REFERENCES `judgehost` (`judgehostid`) ' . $nullClause);
+    }
+
+    public function isTransactional(): bool
+    {
+        return false;
+    }
+}

webapp/src/Entity/DebugPackage.php

@@ -28,7 +28,7 @@ class DebugPackage
     private string $filename;
 
     #[ORM\ManyToOne]
-    #[ORM\JoinColumn(name: 'judgehostid', referencedColumnName: 'judgehostid')]
+    #[ORM\JoinColumn(name: 'judgehostid', referencedColumnName: 'judgehostid', onDelete: 'SET NULL')]
     private Judgehost $judgehost;
 
     public function getDebugPackageId(): int

webapp/src/Entity/JudgeTask.php

@@ -38,7 +38,7 @@ class JudgeTask
     private int $judgetaskid;
 
     #[ORM\ManyToOne(inversedBy: 'judgetasks')]
-    #[ORM\JoinColumn(name: 'judgehostid', referencedColumnName: 'judgehostid')]
+    #[ORM\JoinColumn(name: 'judgehostid', referencedColumnName: 'judgehostid', onDelete: 'SET NULL')]
     #[Serializer\Exclude]
     private ?Judgehost $judgehost = null;
 

webapp/src/Entity/JudgingRun.php

@@ -66,7 +66,7 @@ class JudgingRun extends BaseApiEntity
     private Judging $judging;
 
     #[ORM\ManyToOne(inversedBy: 'judging_runs')]
-    #[ORM\JoinColumn(name: 'testcaseid', referencedColumnName: 'testcaseid')]
+    #[ORM\JoinColumn(name: 'testcaseid', referencedColumnName: 'testcaseid', onDelete: 'CASCADE')]
     #[Serializer\Exclude]
     private Testcase $testcase;
 
@@ -82,7 +82,7 @@ class JudgingRun extends BaseApiEntity
     private Collection $output;
 
     #[ORM\ManyToOne(inversedBy: 'judging_runs')]
-    #[ORM\JoinColumn(name: 'judgetaskid', referencedColumnName: 'judgetaskid')]
+    #[ORM\JoinColumn(name: 'judgetaskid', referencedColumnName: 'judgetaskid', onDelete: 'CASCADE')]
     #[Serializer\Exclude]
     private ?JudgeTask $judgetask = null;
 

webapp/src/Entity/Version.php

@@ -37,11 +37,11 @@ class Version
     private ?string $compilerVersionCommand = null;
 
     #[ORM\ManyToOne(targetEntity: Language::class, inversedBy: "versions")]
-    #[ORM\JoinColumn(name: 'langid', referencedColumnName: 'langid')]
+    #[ORM\JoinColumn(name: 'langid', referencedColumnName: 'langid', onDelete: 'CASCADE')]
     private Language $language;
 
     #[ORM\ManyToOne(targetEntity: Judgehost::class)]
-    #[ORM\JoinColumn(name: 'judgehostid', referencedColumnName: 'judgehostid')]
+    #[ORM\JoinColumn(name: 'judgehostid', referencedColumnName: 'judgehostid', onDelete: 'SET NULL')]
     private Judgehost $judgehost;
 
     #[ORM\Column(