Added migration to make the combination of slug+domain unique

data/migrations/Version20191001201532.php

@@ -0,0 +1,48 @@
+<?php
+declare(strict_types=1);
+
+namespace ShlinkMigrations;
+
+use Doctrine\DBAL\Schema\Index;
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\DBAL\Schema\SchemaException;
+use Doctrine\Migrations\AbstractMigration;
+
+use function array_reduce;
+
+final class Version20191001201532 extends AbstractMigration
+{
+    /**
+     * @throws SchemaException
+     */
+    public function up(Schema $schema): void
+    {
+        $shortUrls = $schema->getTable('short_urls');
+        if ($shortUrls->hasIndex('unique_short_code_plus_domain')) {
+            return;
+        }
+
+        /** @var Index|null $shortCodesIndex */
+        $shortCodesIndex = array_reduce($shortUrls->getIndexes(), function (?Index $found, Index $current) {
+            [$column] = $current->getColumns();
+            return $column === 'short_code' ? $current : $found;
+        });
+        if ($shortCodesIndex === null) {
+            return;
+        }
+
+        $shortUrls->dropIndex($shortCodesIndex->getName());
+        $shortUrls->addUniqueIndex(['short_code', 'domain_id'], 'unique_short_code_plus_domain');
+    }
+
+    /**
+     * @throws SchemaException
+     */
+    public function down(Schema $schema): void
+    {
+        $shortUrls = $schema->getTable('short_urls');
+
+        $shortUrls->dropIndex('unique_short_code_plus_domain');
+        $shortUrls->addUniqueIndex(['short_code']);
+    }
+}