[9.x] Add a new function onlyTrashed (#44989)

* Add a new function `onlyTrashed`

* Add test `onlyTrashed` in `ValidationUniqueRuleTest`

* Update DatabaseRule.php

Co-authored-by: Taylor Otwell <[email protected]>

Author: michaelnabil230

src/Illuminate/Validation/Rules/DatabaseRule.php

@@ -182,6 +182,19 @@ public function withoutTrashed($deletedAtColumn = 'deleted_at')
         return $this;
     }
 
+    /**
+     * Only include soft deleted models during the existence check.
+     *
+     * @param  string  $deletedAtColumn
+     * @return $this
+     */
+    public function onlyTrashed($deletedAtColumn = 'deleted_at')
+    {
+        $this->whereNotNull($deletedAtColumn);
+
+        return $this;
+    }
+
     /**
      * Register a custom query callback.
      *

tests/Validation/ValidationExistsRuleTest.php

@@ -234,6 +234,17 @@ public function testItIgnoresSoftDeletes()
         $this->assertSame('exists:table,NULL,softdeleted_at,"NULL"', (string) $rule);
     }
 
+    public function testItOnlyTrashedSoftDeletes()
+    {
+        $rule = new Exists('table');
+        $rule->onlyTrashed();
+        $this->assertSame('exists:table,NULL,deleted_at,"NOT_NULL"', (string) $rule);
+
+        $rule = new Exists('table');
+        $rule->onlyTrashed('softdeleted_at');
+        $this->assertSame('exists:table,NULL,softdeleted_at,"NOT_NULL"', (string) $rule);
+    }
+
     protected function createSchema()
     {
         $this->schema('default')->create('users', function ($table) {

tests/Validation/ValidationUniqueRuleTest.php

@@ -92,6 +92,17 @@ public function testItIgnoresSoftDeletes()
         $rule->withoutTrashed('softdeleted_at');
         $this->assertSame('unique:table,NULL,NULL,id,softdeleted_at,"NULL"', (string) $rule);
     }
+
+    public function testItOnlyTrashedSoftDeletes()
+    {
+        $rule = new Unique('table');
+        $rule->onlyTrashed();
+        $this->assertSame('unique:table,NULL,NULL,id,deleted_at,"NOT_NULL"', (string) $rule);
+
+        $rule = new Unique('table');
+        $rule->onlyTrashed('softdeleted_at');
+        $this->assertSame('unique:table,NULL,NULL,id,softdeleted_at,"NOT_NULL"', (string) $rule);
+    }
 }
 
 class EloquentModelStub extends Model