diff --git a/README.md b/README.md
index 1376cbe..63de53f 100644
--- a/README.md
+++ b/README.md
@@ -262,19 +262,6 @@ namespace App\Model;
 class Posts extends \InitPHP\Database\Model
 {
 
-    /**
-    * Only if you don't have global connectivity.
-    * 
-    * @var array|string[] 
-    */
-    protected array $connection = [
-        'dsn'           => '', // Database connection address.
-        'username'      => '', // Username with required privileges in the database.
-        'password'      => '', // The password of the database user.
-        'charset'       => 'utf8mb4', // The character set to use in the database.
-        'collation'     => 'utf8mb4_general_ci', // Collection set to use in database
-    ];
-
     /**
      * If not specified, \InitPHP\Database\Entity::class is used by default.
      * 
diff --git a/src/Database.php b/src/Database.php
index 3e56981..d032133 100644
--- a/src/Database.php
+++ b/src/Database.php
@@ -7,7 +7,7 @@
  * @author      Muhammet ŞAFAK <info@muhammetsafak.com.tr>
  * @copyright   Copyright © 2022 Muhammet ŞAFAK
  * @license     ./LICENSE  MIT
- * @version     2.0.7
+ * @version     2.1
  * @link        https://www.muhammetsafak.com.tr
  */
 
@@ -295,29 +295,6 @@ final public function escape_str($value)
         return false;
     }
 
-    /**
-     * @param string $key
-     * @param string|int|float|bool|null $value
-     * @return $this
-     */
-    final public function setParameter(string $key, $value): self
-    {
-        Parameters::set($key, $value);
-        return $this;
-    }
-
-    /**
-     * @param array $parameters
-     * @return $this
-     */
-    final public function setParameters(array $parameters = []): self
-    {
-        foreach ($parameters as $key => $value) {
-            Parameters::set($key, $value);
-        }
-        return $this;
-    }
-
     /**
      * @param string $sqlQuery
      * @param array $parameters
@@ -358,7 +335,7 @@ final public function query(string $sqlQuery, array $parameters = []): Result
                 case self::ARRAY:
                     return $this->_last->asArray();
                 case self::ENTITY:
-                    return $this->_last->asEntity();
+                    return $this->_last->asEntity($this->_credentials['entity'] ?? Entity::class);
                 case self::OBJECT:
                     return $this->_last->asObject();
                 case self::LAZY:
diff --git a/src/Entity.php b/src/Entity.php
index b5db202..fbbd912 100644
--- a/src/Entity.php
+++ b/src/Entity.php
@@ -18,9 +18,9 @@
 class Entity
 {
 
-    private array $_Attributes = [];
+    protected array $__attributes = [];
 
-    private array $_OriginalAttributes = [];
+    protected array $__attributesOriginal = [];
 
     public function __construct(?array $data = [])
     {
@@ -35,10 +35,10 @@ public function __call($name, $arguments)
         switch (\substr($name, 0, 3)) {
             case 'get':
                 $attr = Helper::camelCaseToSnakeCase(\substr($name, 3, -9));
-                return $this->_Attributes[$attr] ?? null;
+                return $this->__attributes[$attr] ?? null;
             case 'set':
                 $attr = Helper::camelCaseToSnakeCase(\substr($name, 3, -9));
-                return $this->_Attributes[$attr] = $arguments[0];
+                return $this->__attributes[$attr] = $arguments[0];
             default:
                 throw new \RuntimeException('There is no "' . $name . '" method.');
         }
@@ -51,7 +51,7 @@ public function __set($name, $value)
             $this->{$methodName}($value);
             return $value;
         }
-        return $this->_Attributes[$name] = $value;
+        return $this->__attributes[$name] = $value;
     }
 
     public function __get($name)
@@ -60,29 +60,29 @@ public function __get($name)
         if(\method_exists($this, $methodName)){
             return $this->{$methodName}();
         }
-        return $this->_Attributes[$name] ?? null;
+        return $this->__attributes[$name] ?? null;
     }
 
     public function __isset($name)
     {
-        return isset($this->_Attributes[$name]);
+        return isset($this->__attributes[$name]);
     }
 
     public function __unset($name)
     {
-        if(isset($this->_Attributes[$name])){
-            unset($this->_Attributes[$name]);
+        if(isset($this->__attributes[$name])){
+            unset($this->__attributes[$name]);
         }
     }
 
     public function __debugInfo()
     {
-        return $this->_Attributes;
+        return $this->__attributes;
     }
 
     public function toArray(): array
     {
-        return $this->_Attributes;
+        return $this->__attributes;
     }
 
     public function getAttributes(): array
@@ -109,7 +109,7 @@ protected function fill(?array $data = null): self
 
     protected function syncOriginal(): self
     {
-        $this->_OriginalAttributes = $this->_Attributes;
+        $this->__attributesOriginal = $this->__attributes;
         return $this;
     }
 
diff --git a/src/Helpers/Helper.php b/src/Helpers/Helper.php
index 1984bc5..763b866 100644
--- a/src/Helpers/Helper.php
+++ b/src/Helpers/Helper.php
@@ -7,7 +7,7 @@
  * @author      Muhammet ŞAFAK <info@muhammetsafak.com.tr>
  * @copyright   Copyright © 2022 Muhammet ŞAFAK
  * @license     ./LICENSE  MIT
- * @version     2.0.8
+ * @version     2.1
  * @link        https://www.muhammetsafak.com.tr
  */
 
@@ -59,7 +59,7 @@ public static function isSQLParameterOrFunction($value): bool
         return ((\is_string($value)) && (
                 $value === '?'
                 || (bool)\preg_match('/^:[\w]+$/', $value)
-                || (bool)\preg_match('/^[a-zA-Z_\.]+$/', $value)
+                || (bool)\preg_match('/^[a-zA-Z_]+[\.]+[a-zA-Z_]+$/', $value)
                 || (bool)\preg_match('/^[a-zA-Z_]+\(\)$/', $value)
             )) || ($value instanceof Raw) || \is_int($value);
     }
diff --git a/src/Model.php b/src/Model.php
index da8d38c..1c67637 100644
--- a/src/Model.php
+++ b/src/Model.php
@@ -7,9 +7,10 @@
  * @author      Muhammet ŞAFAK <info@muhammetsafak.com.tr>
  * @copyright   Copyright © 2022 Muhammet ŞAFAK
  * @license     ./LICENSE  MIT
- * @version     2.0.8
+ * @version     2.1
  * @link        https://www.muhammetsafak.com.tr
  */
+declare(strict_types=1);
 
 namespace InitPHP\Database;
 
@@ -226,6 +227,7 @@ public function __construct()
         $credentials['updatable'] = $this->updatable ?? true;
         $credentials['deletable'] = $this->deletable ?? true;
         $credentials['writable'] = $this->writable ?? true;
+        $credentials['return'] = $this->return ?? self::ENTITY;
         parent::__construct($credentials);
     }
 
diff --git a/src/QueryBuilder.php b/src/QueryBuilder.php
index 659c1da..780509c 100644
--- a/src/QueryBuilder.php
+++ b/src/QueryBuilder.php
@@ -7,16 +7,15 @@
  * @author      Muhammet ŞAFAK <info@muhammetsafak.com.tr>
  * @copyright   Copyright © 2022 Muhammet ŞAFAK
  * @license     ./LICENSE  MIT
- * @version     2.0.8
+ * @version     2.1
  * @link        https://www.muhammetsafak.com.tr
  */
+declare(strict_types=1);
 
 namespace InitPHP\Database;
 
-use InitPHP\Database\Helpers\{Helper, Parameters, Validation};
-use InitPHP\Database\Exceptions\QueryBuilderException;
-use InitPHP\Database\Exceptions\QueryGeneratorException;
-use \InitPHP\Database\Exceptions\ValueException;
+use \InitPHP\Database\Helpers\{Helper, Parameters};
+use \InitPHP\Database\Exceptions\{QueryBuilderException, QueryGeneratorException, ValueException};
 
 class QueryBuilder
 {
@@ -65,6 +64,29 @@ public function exportQB(): array
         return $this->_STRUCTURE;
     }
 
+    /**
+     * @param string $key
+     * @param string|int|float|bool|null $value
+     * @return $this
+     */
+    final public function setParameter(string $key, $value): self
+    {
+        Parameters::set($key, $value);
+        return $this;
+    }
+
+    /**
+     * @param array $parameters
+     * @return $this
+     */
+    final public function setParameters(array $parameters = []): self
+    {
+        foreach ($parameters as $key => $value) {
+            Parameters::set($key, $value);
+        }
+        return $this;
+    }
+
     /**
      * @param string|Raw ...$columns
      * @return $this
@@ -368,7 +390,7 @@ final public function join($table, $onStmt = null, string $type = 'INNER'): self
                 $this->_STRUCTURE['join'][$table] = 'NATURAL JOIN ' . $table;
                 break;
             default:
-                $this->_STRUCTURE['join'][$table] = $type . ' JOIN ' . $table . ' ON ' . $onStmt;
+                $this->_STRUCTURE['join'][$table] = \trim(($type . ' JOIN ' . $table . ' ON ' . $onStmt));
         }
         return $this;
     }
@@ -1124,6 +1146,23 @@ final public function raw(string $rawQuery): Raw
         return new Raw($rawQuery);
     }
 
+    final public function subQuery(\Closure $closure, ?string $alias = null, bool $isIntervalQuery = true): Raw
+    {
+        $queryBuilder = new self();
+        \call_user_func_array($closure, [$queryBuilder]);
+
+        if ($alias !== null && $isIntervalQuery !== TRUE) {
+            throw new QueryBuilderException('To define alias to a subquery, it must be an inner query.');
+        }
+
+        $rawQuery = ($isIntervalQuery === TRUE ? '(' : '')
+            . $queryBuilder->generateSelectQuery()
+            . ($isIntervalQuery === TRUE ? ')' : '')
+            . ($alias !== null ? ' AS ' . $alias : '');
+
+        return $this->raw($rawQuery);
+    }
+
     final public function generateInsertQuery(): string
     {
         if (!empty($this->_STRUCTURE['table'])) {
@@ -1533,7 +1572,7 @@ private function whereOrHavingStatementPrepare($column, $value, string $mark = '
                         }
                         $values[] = Helper::isSQLParameterOrFunction($val) ? $val : Parameters::add($column, $val);
                     }
-                    $value = \implode(', ', \array_unique($values));
+                    $value = '(' . \implode(', ', \array_unique($values)) . ')';
                 } elseif (Helper::isSQLParameterOrFunction($value)) {
                     $value = (string)$value;
                 }else{
@@ -1541,7 +1580,7 @@ private function whereOrHavingStatementPrepare($column, $value, string $mark = '
                 }
                 return $column
                     . ($searchMark === 'NOTIN' ? ' NOT ' : ' ')
-                    . 'IN (' . $value . ')';
+                    . 'IN ' . $value;
             case 'FINDINSET':
             case 'NOTFINDINSET':
                 if(\is_array($value)){
diff --git a/tests/QueryBuilderUnitTest.php b/tests/QueryBuilderUnitTest.php
index 230e384..ee1bc94 100644
--- a/tests/QueryBuilderUnitTest.php
+++ b/tests/QueryBuilderUnitTest.php
@@ -420,4 +420,33 @@ public function testJoinClosureGive()
         $this->db->reset();
     }
 
+    public function testSubQuery()
+    {
+        Parameters::reset();
+        $this->db->select('u.name')
+            ->from('users AS u')
+            ->in('u.id', $this->db->subQuery(function (QueryBuilder $builder) {
+                $builder->select('id')
+                    ->from('roles')
+                    ->where('name', 'admin');
+            }));
+        $expected = 'SELECT u.name FROM users AS u WHERE u.id IN (SELECT id FROM roles WHERE name = :name)';
+        $this->assertEquals($expected, $this->db->generateSelectQuery());
+        $this->db->reset();
+
+
+        Parameters::reset();
+        $this->db->select('u.name, p.title')
+            ->from('users AS u')
+            ->join($this->db->subQuery(function (QueryBuilder $builder) {
+                $builder->select('id, title, user_id')
+                    ->from('posts')
+                    ->where('user_id', 5);
+            }, 'p'), 'p.user_id = u.id', '');
+
+        $expected = 'SELECT u.name, p.title FROM users AS u JOIN (SELECT id, title, user_id FROM posts WHERE user_id = 5) AS p ON p.user_id = u.id WHERE 1';
+        $this->assertEquals($expected, $this->db->generateSelectQuery());
+        $this->db->reset();
+    }
+
 }