我有学校的项目，建立电子商务，经过一些研究，我发现创建不同的数据库的产品形象是很好的做法，但在这里，我面临的形象，以连接两个不同的表的所有表。我有两个不同的数据库类名。

• 1. $db = Database::newInstance();
• 2. $dtb = Idatabase::newInstance();

1. $db = Database::newInstance();这具有表名products具有列puid，products_attribute_01具有列puid，products_inventory具有列puid。
2.$dtb = Idatabase::newInstance();它具有表名pd_images和列puid

如何连接所有表

这是我正在尝试的，但给出错误Fatal error: Uncaught Error: Object of class Database could not be converted to string in 18

$db = Database::newInstance();
$dbname1 = $db->getDbName();
$dtb = Idatabase::newInstance();
$dbname2 = $dtb->getDb_Name();
$data = array();
$sql = "SELECT *
FROM $dbname1.products
INNER JOIN $dbname1.products_attribute_01 ON products.puid = products_attribute_01.puid
INNER JOIN $dbname1.products_inventory ON products.puid = products_inventory.puid
UNION ALL
SELECT *
FROM $dbname2.images.pd_images";
$row1 = $db->read($sql, $data);
var_dump($row1); 
$data['row1'] = $row1;

这里是数据库

Class Database{
    //This is Database class
    public static $conn;

    public function __construct(){

        try {

            $string = DB_TYPE.":host=".DB_HOST.";dbname=".DB_NAME;
            self::$conn = new PDO($string,DB_USER,DB_PASS);

        } catch (PDOException $e) {
            die($e->getMessage());
        }

    }
    public static function getDbName(){
        return DB_NAME;
        }
    public static function getInstance(){

        if (self::$conn) {
           return self::$conn; 
        }
        return $instance = new self();
    }
    public static function newInstance(){
        return $instance = new self();
    }
    //read from database
    public function read($query,$data = array()) {
        
        $statement = self::$conn->prepare($query);
        $result = $statement->execute($data);

        if ($result) {
            $data = $statement->fetchAll(PDO::FETCH_OBJ);
            if (is_array($data) && count($data) > 0) {
                return $data;
            }
        }
        
        return false;
    }
    //write from database
    public function write($query,$data = array()){

        $statement = self::$conn->prepare($query);
        $result = $statement->execute($data);

        if ($result) {
            
            return true;
        }
        return false;
    }

}

我现在已添加此内容

public static function getDbName(){
return DB_NAME;
}