Magento can't find the class model

Question

I am new with Magento. And trying to create my own model.
So I start with a small test
The model folder structure as the following:

FirstStore/Demo/block 
FirstStore/Demo/etc/config.xml
FirstStore/Demo/controller
FirstStore/Demo/Model/Product.php
FirstStore/Demo/Helper
FirstStore/Demo/sql

the etc/config.xml code:

<?xml version="1.0" encoding="UTF-8"?>
<config>
<modules>
    <version>0.0.1</version>
</modules>
</config>

and the Model/Product.php code:

class FirstStore_Demo_Model_Product
{
public function sayhello(){
    echo 'Hello , World with Magento';
}
}

and the app/etc/modules/FirstStore_Demo.xml code:

<?xml version="1.0"?>
<config>
<modules>
    <FirstStore_Demo>
        <active>true</active>
        <codePool>local</codePool>
    </FirstStore_Demo>
</modules>
</config>  

finally I am running this code under test.php page at the magento root dir
the test.php code:

require_once 'app/Mage.php';
Mage::app();

$product = new FirstStore_Demo_Model_Product;
$product->sayhello();

the error at localhost/magento/test.php is:

Fatal error: Class 'FirstStore_Demo_Model_Product' not found in C:\xampp\htdocs\php\magento\test.php

Answer 1

Magento does not yet support PHP 5.6 officially as the version you stated using in your comments. Please check the System Requirements page for supported software.

Especially in combination with XAMPP it might cause unexpected issues. I would advice you to downgrade to PHP 5.5.

Answer 2

Your model file, does not seem to extends the core class don't forget extends Mage_Core_Model_Abstract in the definition of your model class.. so it would be

class FirstStore_Demo_Model_Product extends Mage_Core_Model_Abstract
{
    public function sayhello(){
        echo 'Hello , World with Magento';
    }
}

Moreover you need to add your model declaration in your config.xml as someone wisely suggested

<models>

          <firststore_demo>
                   <class>FirstStore_Demo_Model</class>
          </firststore_demo>
</models>

Answer 3

Maybe you could solve this using routers, take a look to this question and its answer.

My first Hello World from a module and model and I can't load the model

Answer 4

You ought to try

$productModel = Mage::getModel('firststore_demo/product');

And add to your config.xml

<models>

          <firststore_demo>
                   <class>FirstStore_Demo_Model</class>
          </firststore_demo>
</models>