Uncaught Error: Call to a member function fetchAll() on boolean

index.php:

$db = new Db();
$param = [':name' => 'Alex'];
$data = $db->sql('select * from test where name = :name',$param)->query();
var_dump($data);

and get the error :

 Fatal error: Uncaught Error: Call to a member function fetchAll() on boolean 

Db.php

   public function sql($sql,array $params = null)
    {   
        $sql = $this->connection->prepare($sql);

        if($params){
            foreach ($params as $key => $param) {
                $sql->bindParam($key, $param);
            }
        }

        $this->statement = $sql;
        return $this; 
    }


    public function query($type = 1)
    {
      $statement = $this->statement->execute();

      return ($type == 1) ? $statement->fetchAll(static::$DB_FETCH) : $statement->fetch(static::$DB_FETCH);
    }

If I running in the sql() method, execute() and fetch() the data inside it , it can truly get the data , but put the execute() and fetch() to the query() method, getting the error message, Any Idea? ;

Answer

There is an error in your code. In this line:

$statement = $this->statement->execute();

The execute() method is PDOStatement::execute. This is the signature:

public bool PDOStatement::execute ([ array $input_parameters ] )

Which means it returns boolean. Your mistake is you are trying to call fetchAll() on a boolean.

For more information about the error message, see this page.