PHP PDO CRUD类调用非对象上的成员函数rowCount（）

Question

I'm just getting started using PDO to move away from mysqli but hit a problem. I'm following a tutorial and I want to return an array from the database but I get the following error:

Fatal error: Call to a member function rowCount() on a non-object in C:\\xampp\\htdocs\\phptuts\\crud\\core\\managedb.class.php on line 27

Here is my managedb.php class:

<?php

class ManageDatabase
{

    public $link;

    function __construct()
    {
        include_once('database.class.php');
        $conn = new database;
        $this->link = $conn->connect();
        return $this->link;
    }

    function getData($table_name, $id=null)
    {
        if(isset($id))
    {
        $query = $this->link->query("SELECT * FROM $table_name WHERE id = '$id' ORDER BY id ASC");
    }
    else
    {
        $query = $this->link->query("SELECT * FROM $table_name ORDER BY id ASC");
    }

    $rowCount = $query->rowCount();
    if($rowCount >= 1)
    {
        $result = $query->fetchAll();
    }
    else
    {
        $result = 0;
    }
    return $result;
}

}

Then I'm simply using the following code to try and get a response:

<?php

include_once('../core/managedb.class.php');
$init = new ManageDatabase;

$table_name = 'users';
$data = $init->getData($table_name);

print_r($data);

This is when I get the error, Any ideas?

Answer 1

I'd var_dump($query) before the $rowCount = $query->rowCount(); line to see what it actually is, because apparently it's not an object. I'm guessing it's either NULL or empty because the whole $this-link->query(<sql statement>); didn't return what you expected

Answer 2

A couple of things to check out:

From the PHP manual :

PDO::query() returns a PDOStatement object, or FALSE on failure.

You'll want to test if the query succeed and if not, why. You can check the error using PDO's errorInfo function:

if ($query == false) 
{
    print_r($this->link->errorInfo());
    exit();
}

Another thing to note is that rowCount() in PDO returns the affected rows from a INSERT / UPDATE / DELETE type statement. For a SELECT you may get a row count, or you may not. The manual suggests a separate query to find the number of rows, but in your instance it might be easier testing if you get anything back from fetchAll():

$result = $query->fetchAll();
if (!empty($result)) 
{
    return $result;
} 
else 
{
    return 0;
}