Add marker for auditable models without owner

Models implementing AuditableWithoutOwner intentionally have no audit
owner, either because they belong to neither an organization nor a user,
or because they and their audits have to be kept when the owner is
deleted (for example billing records). Adds helpers and a scope on the
audit model to find audits that are missing an owner although they
should have one.

app/Models/Audit.php

@@ -4,9 +4,12 @@ declare(strict_types=1);
 
 namespace App\Models;
 
+use App\Models\Concerns\AuditableWithoutOwner;
 use Database\Factories\AuditFactory;
+use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\Relation;
 use Illuminate\Support\Carbon;
 use OwenIt\Auditing\Models\Audit as PackageAuditModel;
 
@@ -31,6 +34,7 @@ use OwenIt\Auditing\Models\Audit as PackageAuditModel;
  * @property-read Organization|null $ownerOrganization
  *
  * @method static AuditFactory factory()
+ * @method static Builder<Audit> whereMissingOwner()
  */
 class Audit extends PackageAuditModel
 {
@@ -52,4 +56,41 @@ class Audit extends PackageAuditModel
     {
         return $this->belongsTo(Organization::class, 'owner_organization_id');
     }
+
+    /**
+     * Whether audits of the given auditable type intentionally have no owner (see AuditableWithoutOwner).
+     */
+    public static function isAuditableTypeWithoutOwner(string $auditableType): bool
+    {
+        $modelClass = Relation::getMorphedModel($auditableType) ?? $auditableType;
+
+        return is_subclass_of($modelClass, AuditableWithoutOwner::class);
+    }
+
+    /**
+     * Auditable types (morph aliases) whose audits intentionally have no owner (see AuditableWithoutOwner).
+     *
+     * @return array<int, string>
+     */
+    public static function getAuditableTypesWithoutOwner(): array
+    {
+        return collect(Relation::morphMap())
+            ->filter(fn (string $modelClass): bool => is_subclass_of($modelClass, AuditableWithoutOwner::class))
+            ->keys()
+            ->values()
+            ->all();
+    }
+
+    /**
+     * Audits that have neither an owner organization nor an owner user, although their auditable type should have one.
+     * These are audits whose owner no longer exists or could not be determined (yet).
+     *
+     * @param  Builder<Audit>  $builder
+     */
+    public function scopeWhereMissingOwner(Builder $builder): void
+    {
+        $builder->whereNull('owner_organization_id')
+            ->whereNull('owner_user_id')
+            ->whereNotIn('auditable_type', self::getAuditableTypesWithoutOwner());
+    }
 }

app/Models/Concerns/AuditableWithoutOwner.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models\Concerns;
+
+/**
+ * Marks an auditable model whose audits intentionally have no owner (neither an organization nor a user),
+ * either because the model belongs to neither of them, or because the model and its audits have to be kept
+ * when its organization or user is deleted (for example billing records).
+ * Audits of these models are not deleted together with an organization or user,
+ * and are not considered as missing an owner (for example by the audit backfill command).
+ */
+interface AuditableWithoutOwner {}