How to Import large CSV file in Drupal with Batch API , Beginners Guide Part I

Recently i have worked on a project which has lots of (in lakhs) data, I have a CSV file which we need to import in database, suppose the CSV have arround 2 lacks data, so when i try to import it then ststem consums too much time and gives the timeout error and failed to upload, to resole these type of issue the Batch API comes in My mind,

Why use batch API,

Batch API makes a queue of operations and performs each operations one by one, so system did not give the timeout issue, and batch API also shows the status of uploading and remaning data,

Here i am assuming you have basic knowledge of drupal module development,

Step -1: create a module within your drupal application, Lets assume module name is dharmend, Now i am going to create a menu , so i have added hook_menu in module file

 <?php  
 /* implement hook_menu to create a new menu,  
 *  
 */  
 function dharmend_menu(){  
      $items['csvImporter'] = array(  
     'title' => t('Upload Data From CSV File'),  
     'access callback' => 'user_access',  
     //'access arguments' => array('Import CSV labour data'),  
     'page callback' => 'csvImporter_pagecallback',  
     'type' => MENU_NORMAL_ITEM,  
    );  
    return $items ;  
 }  

Step-2 Now declare the callback function of the menu,

 /*  
 * menu Callback function  
 */  
 function csvImporter_pagecallback(){  
   $module_path = drupal_get_path('module', 'dharmend');  
   $form = drupal_get_form('csvImporter_form');  
   $output .= drupal_render($form);  
   return $output;  
  }  
  function csvImporter_form() {  
   $form['#attributes'] = array(  
     'enctype' => 'multipart/form-data'  
   );  
   $form['csvfile'] = array(   
    '#title' => t('CSV File'),  
    '#type' => 'file',  
    '#description' => ($max_size = parse_size(ini_get('upload_max_filesize'))) ? t('Due to server restrictions, the <strong>maximum upload file size is !max_size</strong>. Files that exceed this size will be disregarded.', array('!max_size' => format_size($max_size))) : '',    
   ) ;  
   $form['submit'] = array(  
    '#type' => 'submit',  
    '#value' => t('CSV Import'),  
   ) ;  
   $form['#validate'] = array(  
    'csvImporter_validate_fileupload',  
    'csvImporter_form_validate',  
   ) ;  
   return $form ;  
  }  

So here you can see that first i have created a new form to upload the csv file ,

Step -3 Add validate function to validate and upload file on server,

 function csvImporter_form_validate(&$form, &$form_state) {  
   if ( isset( $form_state['values']['csvupload'] ) ) {  
    if ( $handle = fopen($form_state['values']['csvupload'], 'r') ) {  
     $line_count = 1 ;  
     $first = TRUE ;  
     $counter = 0;  
     while($line = fgetcsv($handle)){//if ($line = fgetcsv($handle)){ //while($line = fgetcsv($handle)){  
       //drupal_set_message('Total row cont on csv'.count($line).'');  
     }  
     fclose($handle);  
    }  
    else {  
     form_set_error('csvfile', t('Unable to read uploaded file !filepath', array('!filepath' => $form_state['values']['csvupload'])));  
    }  
   }  
  }