[11.x] Add the pivot's related model when creating from attributes

src/Illuminate/Database/Eloquent/Relations/Concerns/AsPivot.php

@@ -14,6 +14,13 @@ trait AsPivot
      */
     public $pivotParent;
 
+    /**
+     * The related model of the relationship.
+     *
+     * @var \Illuminate\Database\Eloquent\Model
+     */
+    public $pivotRelated;
+
     /**
      * The name of the foreign key column.
      *
@@ -214,6 +221,19 @@ public function setPivotKeys($foreignKey, $relatedKey)
         return $this;
     }
 
+    /**
+     * Set the related model of the relationship.
+     *
+     * @param  \Illuminate\Database\Eloquent\Model|null  $related
+     * @return $this
+     */
+    public function setRelatedModel(?Model $related = null)
+    {
+        $this->pivotRelated = $related;
+
+        return $this;
+    }
+
     /**
      * Determine if the pivot model or given attributes has timestamp attributes.
      *
@@ -326,6 +346,7 @@ protected function newQueryForCollectionRestoration(array $ids)
     public function unsetRelations()
     {
         $this->pivotParent = null;
+        $this->pivotRelated = null;
         $this->relations = [];
 
         return $this;

src/Illuminate/Database/Eloquent/Relations/Concerns/InteractsWithPivotTable.php

@@ -502,7 +502,9 @@ protected function getCurrentlyAttachedPivots()
 
             $pivot = $class::fromRawAttributes($this->parent, (array) $record, $this->getTable(), true);
 
-            return $pivot->setPivotKeys($this->foreignPivotKey, $this->relatedPivotKey);
+            return $pivot
+                ->setPivotKeys($this->foreignPivotKey, $this->relatedPivotKey)
+                ->setRelatedModel($this->related);
         });
     }
 
@@ -521,7 +523,9 @@ public function newPivot(array $attributes = [], $exists = false)
             $this->parent, $attributes, $this->table, $exists, $this->using
         );
 
-        return $pivot->setPivotKeys($this->foreignPivotKey, $this->relatedPivotKey);
+        return $pivot
+            ->setPivotKeys($this->foreignPivotKey, $this->relatedPivotKey)
+            ->setRelatedModel($this->related);
     }
 
     /**

src/Illuminate/Database/Eloquent/Relations/MorphToMany.php

@@ -160,6 +160,7 @@ public function newPivot(array $attributes = [], $exists = false)
                         : MorphPivot::fromAttributes($this->parent, $attributes, $this->table, $exists);
 
         $pivot->setPivotKeys($this->foreignPivotKey, $this->relatedPivotKey)
+              ->setRelatedModel($this->related)
               ->setMorphType($this->morphType)
               ->setMorphClass($this->morphClass);
 

tests/Database/DatabaseEloquentPivotTest.php

@@ -35,6 +35,7 @@ public function testPropertiesAreSetCorrectly()
         $this->assertSame('connection', $pivot->getConnectionName());
         $this->assertSame('table', $pivot->getTable());
         $this->assertTrue($pivot->exists);
+        $this->assertSame($parent, $pivot->pivotParent);
     }
 
     public function testMutatorsAreCalledFromConstructor()