[12.x] Return early on belongs-to-many relationship syncWithoutDetaching method when empty values are given (#56157)

* Prevent unnecessary sync when IDs are empty and detaching is false

* Add test for sync with empty array and detaching disabled

* Test with all empty values

* Rearrange precedence of methods

* Tweak test

* Disable query log after sync test

Author: stevebauman

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

@@ -87,14 +87,18 @@ public function sync($ids, $detaching = true)
             'attached' => [], 'detached' => [], 'updated' => [],
         ];
 
+        $records = $this->formatRecordsList($this->parseIds($ids));
+
+        if (empty($records) && ! $detaching) {
+            return $changes;
+        }
+
         // First we need to attach any of the associated models that are not currently
         // in this joining table. We'll spin through the given IDs, checking to see
         // if they exist in the array of current ones, and if not we will insert.
         $current = $this->getCurrentlyAttachedPivots()
             ->pluck($this->relatedPivotKey)->all();
 
-        $records = $this->formatRecordsList($this->parseIds($ids));
-
         // Next, we will take the differences of the currents and given IDs and detach
         // all of the entities that exist in the "current" array but are not in the
         // array of the new IDs given to the method which will complete the sync.

tests/Integration/Database/EloquentBelongsToManyTest.php

@@ -909,6 +909,27 @@ public function testSyncWithoutDetachingMethod()
         );
     }
 
+    public function testSyncMethodWithEmptyValueDoesNotQueryWhenDetachingDisabled()
+    {
+        $post = Post::create(['title' => Str::random()]);
+
+        DB::enableQueryLog();
+
+        foreach ([collect(), [], null] as $value) {
+            $result = $post->tags()->sync($value, false);
+
+            $this->assertEquals([
+                'attached' => [],
+                'detached' => [],
+                'updated' => [],
+            ], $result);
+        }
+
+        $this->assertEmpty(DB::getQueryLog());
+
+        DB::disableQueryLog();
+    }
+
     public function testToggleMethod()
     {
         $post = Post::create(['title' => Str::random()]);