From c6edb411349fea6f158fef71245615fd3d3f7d0a Mon Sep 17 00:00:00 2001
From: Samuel Georges <sam@daftspunk.com>
Date: Tue, 20 Feb 2024 17:58:42 +1100
Subject: [PATCH] Detect and preserve shared multisite relationships

---
 src/Database/Concerns/HasRelationships.php | 51 +++++++++++++---------
 src/Database/Traits/Multisite.php          | 26 ++++++++++-
 2 files changed, 55 insertions(+), 22 deletions(-)

diff --git a/src/Database/Concerns/HasRelationships.php b/src/Database/Concerns/HasRelationships.php
index 60f132402..6e65fb53f 100644
--- a/src/Database/Concerns/HasRelationships.php
+++ b/src/Database/Concerns/HasRelationships.php
@@ -876,42 +876,51 @@ protected function setRelationSimpleValue($relationName, $value)
     }
 
     /**
-     * performDeleteOnRelations locates relations with delete flag and cascades
-     * the delete event.
+     * performDeleteOnRelations locates relations with delete flag and cascades the
+     * delete event. This is called before the parent model is deleted. This method
+     * checks in with the Multisite trait to preserve shared relations.
+     *
+     * @see \October\Rain\Database\Traits\Multisite::canDeleteMultisiteRelation
      */
     protected function performDeleteOnRelations()
     {
         $definitions = $this->getRelationDefinitions();
+        $useMultisite = $this->isClassInstanceOf(\October\Contracts\Database\MultisiteInterface::class) && $this->isMultisiteEnabled();
+
         foreach ($definitions as $type => $relations) {
-            // Hard 'delete' definition
             foreach ($relations as $name => $options) {
-                if (!Arr::get($options, 'delete', false)) {
-                    continue;
-                }
-
-                if (!$relation = $this->{$name}) {
+                // Detect and preserve shared multisite relationships
+                if ($useMultisite && !$this->canDeleteMultisiteRelation($name, $type)) {
                     continue;
                 }
 
-                if ($relation instanceof EloquentModel) {
-                    $relation->forceDelete();
-                }
-                elseif ($relation instanceof CollectionBase) {
-                    $relation->each(function ($model) {
-                        $model->forceDelete();
-                    });
-                }
-            }
-
-            // Belongs-To-Many should clean up after itself by default
-            if ($type === 'belongsToMany') {
-                foreach ($relations as $name => $options) {
+                // Belongs-To-Many should clean up after itself by default
+                if ($type === 'belongsToMany') {
                     if (!Arr::get($options, 'detach', true)) {
                         return;
                     }
 
                     $this->{$name}()->detach();
                 }
+                // Hard 'delete' definition
+                else {
+                    if (!Arr::get($options, 'delete', false)) {
+                        continue;
+                    }
+
+                    if (!$relation = $this->{$name}) {
+                        continue;
+                    }
+
+                    if ($relation instanceof EloquentModel) {
+                        $relation->forceDelete();
+                    }
+                    elseif ($relation instanceof CollectionBase) {
+                        $relation->each(function ($model) {
+                            $model->forceDelete();
+                        });
+                    }
+                }
             }
         }
     }
diff --git a/src/Database/Traits/Multisite.php b/src/Database/Traits/Multisite.php
index 815702078..b25fc9450 100644
--- a/src/Database/Traits/Multisite.php
+++ b/src/Database/Traits/Multisite.php
@@ -158,7 +158,31 @@ protected function defineMultisiteRelations()
     }
 
     /**
-     * defineMultisiteRelation
+     * canDeleteMultisiteRelation checks if a relation has the potential to be shared with
+     * the current model. If there are 2 or more records in existence, then this method
+     * will prevent the cascading deletion of relations.
+     *
+     * @see \October\Rain\Database\Concerns\HasRelationships::performDeleteOnRelations
+     */
+    public function canDeleteMultisiteRelation($name, $type = null): bool
+    {
+        if ($type === null) {
+            $type = $this->getRelationType($name);
+        }
+
+        if (!in_array($type, ['belongsToMany', 'belongsTo', 'hasOne', 'hasMany', 'attachOne', 'attachMany'])) {
+            return false;
+        }
+
+        // The current record counts for one so halt if we find more
+        return !($this->newOtherSiteQuery()->count() > 1);
+    }
+
+    /**
+     * defineMultisiteRelation will modify defined relations on this model so they share
+     * their association using the shared identifier (`site_root_id`). Only these relation
+     * types support relation sharing: `belongsToMany`, `belongsTo`, `hasOne`, `hasMany`,
+     * `attachOne`, `attachMany`.
      */
     protected function defineMultisiteRelation($name, $type = null)
     {