Add the following method in your controller to override the default method to fix the 404 error.

protected function _isAllowed()
    {
        return true;
    }

Which will solve your problem.

Add the following code in your config.php file under the tag.

    
                        
            My Default Value         
              
    

Example :

system.xml file

    
        
            New Settings
            309
        
    
        

        
                New Settings
                352
                1
                1
                1
                Your_tab
                
                
					New Settings
					
                    12
                    1
                    1
                    1
                    
                        
                             - Add a value
                            text
                            1
                            1
                            1
                            1
			    Your settings.
                        
                    

                
                
            
         

  
		

For Setting The default value of the field : demo_field you have to add following code in config.xml

	
		
			0.1.0
		
	
        
			
				YourCompany_Your_module_Helper
			
        
      
       
        
            
                
                    
                        
                            
                                
                                 
                                        
                                        101
                                  
                                
                            
                        
                    
                 
            
        
     
     
    
    
                        
            1         
              
     

Which will look with default value 1 as :

magento set default value for config defined value

You can add yes/ no dropdown in magento admin by adding simply the following code in system.xml file:

       
                
                             - Select - 
                            select
                            adminhtml/system_config_source_yesno
                            1
                            1
                            1
                            1
			     Your comment.
                 
         

Which will generate the select box like this –

Magento admin select yes/ no dropdown

Magento redirect from phtml or model or helper or block or observer Example

Example :

Mage::app()->getResponse()->setRedirect('checkout/onepage');

or

Mage::app()->getResponse()->setRedirect('checkout/onepage');
exit;

Magento set Order() not working

An alternate way to sort magento collection is

$collection = Mage::getModel('test/test')
->getCollection()
->getSelect()
->order('id DESC');

This will sort the magento collection in descending order by id.

Magento add order by to collection : You can simply add the order in magento collection
by adding the –>setOrder(field_name, ASC_DESC); as below

$collection = Mage::getModel('test/test')
->getCollection()
->setOrder('id', 'DESC');

The above example will sort the collection in descending order by id.

Magento set order for grid collection :

You simply add order in magento admin grid collection.
Go to your grid.php file and change order in construct.

setId('YourGridId');
        $this->setDefaultSort('id');
        $this->setDefaultDir('DESC');
        $this->setSaveParametersInSession(true);
        $this->setUseAjax(true);
    }

}
?>

You can add sorting as per your need by Changing this –
$this->setDefaultSort(‘id’);
$this->setDefaultDir(‘DESC’);

How to connect to another database in magento :

For Connecting to another database rather than using the current database you need to define new resource in config.php and tell magento to use this resource.

    
        
            0.1.1
        
    
    
        
            
                
                    anotherexternal_database
                
            
            
                
                    anotherexternal_database
                
            
            
                
                    core_setup
                
            
            
                
                    
                    
                    
                    
                    mysql4
                    pdo_mysql
                    1
                
            
        
    

Now you can access Database as below :

getConnection('anotherexternaldb_read');
    $data   = $connection->query("SELECT * FROM customers");
 
	


?>

Magento get current category id
You can get current categeory id as below :

$layer = Mage::getSingleton('catalog/layer');
$Category = $layer->getCurrentCategory();
$currentCatId= $Category ->getId(); //will give current categeory id