PDOStatement无法转换为字符串

Question

所以价格从数据库中获得两倍，每当我尝试执行这段代码或转换它时，我得到：

  

捕获致命错误：PDOStatement类的对象无法转换为字符串

try{    
    $conn = new PDO('mysql:host=localhost;dbname=janes_catering', $username,   
    $password); 
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $price = $conn->query("SELECT cost FROM foods WHERE description = 
    ':choice' AND size = ':oice'");
    $stmt = $conn->prepare("INSERT foods(description, size, cost) 
    VALUES ( :choice, :oice, :price)");
    $TPrice = (string)$price;
    $stmt->bindParam(':choice', $choice, PDO::PARAM_STR);
    $stmt->bindParam(':TPrice', $TPrice,  PDO::PARAM_STR);
    $stmt->bindParam(':oice', $oice, PDO::PARAM_STR);

    $stmt->execute();           
}