Adding some performance indices and cleaning up some annotation mess.

app/model/entity/Exercise.php

@@ -120,9 +120,9 @@ public function getAuthor() {
   protected $isLocked;
 
   /**
-   * @ORM\Column(type="boolean")
+   * @ORM\Column(type="boolean", options={"default":0})
    */
-  protected $isBroken;
+  protected $isBroken = false;
 
   public function isPublic() {
     return $this->isPublic;

app/model/entity/Group.php

@@ -172,7 +172,7 @@ public function isDirectlyArchived(): bool {
   }
 
   /**
-   * @ORM\Column(type="boolean")
+   * @ORM\Column(type="boolean", options={"default":0})
    */
   protected $isOrganizational = false;
 

app/model/entity/Solution.php

@@ -13,6 +13,8 @@
 
 /**
  * @ORM\Entity
+ * @ORM\Table(indexes={@ORM\Index(name="created_at_idx", columns={"created_at"})})
+ * 
  * @method string getId()
  * @method Collection getFiles()
  * @method RuntimeEnvironment getRuntimeEnvironment()

app/model/entity/base/ExerciseData.php

@@ -7,7 +7,7 @@
 
 trait ExerciseData {
   /**
-   * @ORM\Column(type="string")
+   * @ORM\Column(type="string", options={"default":"simpleExerciseConfig"})
    */
   protected $configurationType;
 

app/model/entity/base/Submission.php

@@ -10,6 +10,7 @@
 
 /**
  * @ORM\MappedSuperclass
+ * @ORM\Table(indexes={@ORM\Index(name="submitted_at_idx", columns={"submitted_at"})})
  *
  * @method string getId()
  * @method string getResultsUrl()

migrations/Version20190504100254.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Migrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Auto-generated Migration: Please modify to your needs!
+ */
+final class Version20190504100254 extends AbstractMigration
+{
+    public function getDescription() : string
+    {
+        return '';
+    }
+
+    public function up(Schema $schema) : void
+    {
+        // this up() migration is auto-generated, please modify it to your needs
+        $this->abortIf($this->connection->getDatabasePlatform()->getName() !== 'mysql', 'Migration can only be executed safely on \'mysql\'.');
+
+        $this->addSql('CREATE INDEX submitted_at_idx ON assignment_solution_submission (submitted_at)');
+        $this->addSql('CREATE INDEX submitted_at_idx ON reference_solution_submission (submitted_at)');
+        $this->addSql('CREATE INDEX created_at_idx ON solution (created_at)');
+    }
+
+    public function down(Schema $schema) : void
+    {
+        // this down() migration is auto-generated, please modify it to your needs
+        $this->abortIf($this->connection->getDatabasePlatform()->getName() !== 'mysql', 'Migration can only be executed safely on \'mysql\'.');
+
+        $this->addSql('DROP INDEX submitted_at_idx ON assignment_solution_submission');
+        $this->addSql('DROP INDEX submitted_at_idx ON reference_solution_submission');
+        $this->addSql('DROP INDEX created_at_idx ON solution');
+    }
+}