2.11.9 User Guide

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Module Tutorial

The best way to understand ExpressionEngine modules is to dissect one. Thus we present the ‘third party’ Download module. This module is fairly typical, and includes a backend control panel, its own database tables, adds a tab with fields to the publish page, and in general uses all of the standard files used in module creation.

The Download module will allow an administrator to select files from the upload directories and create a download record for them. As part of that record, they will specify access restrictions based on member groups. These ‘downloads’ can then be displayed or accessed through a ‘forced download’ without revealing the file’s true path. Through a ‘Download’ tab to the publish page, multiple ‘Downloads’ can be associated with an entry and displayed or linked inside a standard channel entries tag.

The full example module can be downloaded from GitHub.


if you have not already read the Modules Overview, you will want to do so in order to obtain the greatest value from the tutorial.

Required File Structure for the Download Module

Our module is named ‘Download’, and that name will form the basis for much of our file naming conventions. Based on this name, we need to create a folder named ‘download’ in ExpressionEngines’s third party package folder:


Inside that folder, there are 4 required files. In addition, this module adds a tab to the publish page, and we will have numerous view files used in the display of our backend. The final file structure will be:

  • third_party/download/ - installs, uninstalls and updates the module
  • third_party/download/ - the backend control panel
  • third_party/download/ - the core module file, which process module tags used in templates
  • third_party/download/language/english/download_lang.php - the ‘english’ language file
  • third_party/download/ - generates our tab on the publish page and process publish page submissions
  • third_party/download/views/index.html - multiple view files inside the view folder

The Update file (

The Update file for a module includes a class with a name that is a combination of the package’s name with _upd tacked on the end. So, for our download module, we will create a class called Download_upd. There is only one required class variable for this class and that is $version, which should indicate the current version of this module:

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Download_upd {

    var $version = '1.0';

Each Control Panel class has at a minimum three functions: install(), uninstall() and update(). These functions are required even if your module has no Control Panel side functionality. In addition, the Download module requires the tabs() function, as it adds a tab to the publish page.

Installation Function

Here is what our Download module’s installation function will look like. Basically, it inserts the module’s name, version, and whether it has a backend and/or a tab into the exp_modules table (see Active Record class). Since our module will have a Control Panel backend, we set the third field to 'y', otherwise it should be set to 'n'. Since our module will also add a tab to the publish field, we need to set has_publish_fields to 'y' as well:

function install()

    $data = array(
        'module_name' => 'Download' ,
        'module_version' => $this->version,
        'has_cp_backend' => 'y',
        'has_publish_fields' => 'y'

    ee()->db->insert('modules', $data);

The Download module also requires that we generate an action id, to be used to serve up files based on the id associated with a given file record. Adding the following query to our installer will generate that action id and tie it to the appropriate method:

$data = array(
    'class'     => 'Download' ,
    'method'    => 'force_download'

ee()->db->insert('actions', $data);


Because the action_id field in the actions table is auto-incremented, do not specify it in the query. If you include an auto-increment field and leave it empty, it will cause a database error if MySQL is running in “strict mode”.

When the actions are entered into the exp_actions database table, they are given a unique action_id that the system will recognize and use to call the class and function required. If you need to use this id in the control panel, you can use the CP class fetch_action_id() function in your control panel files:

$action_id  = ee()->cp->fetch_action_id('Download', 'force_download');

When using an action id on the frontend (in your file), you use the Functions class fetch_action_id(), which outputs the appropriate tag for the template parser to process:

$action_id  = ee()->functions->fetch_action_id('Download', 'force_download');

The installation function will also need to create the database tables that we will use to store the download data and relationships (see Database Forge class):

$fields = array(
    'file_id'   => array('type' => 'int', 'constraint' => '10', 'unsigned' => TRUE, 'auto_increment' => TRUE),
    'dir_id'    => array('type' => 'int', 'constraint'  => '4'),
    'file_name' => array('type' => 'varchar', 'constraint' => '250'),
    'file_title'    => array('type' => 'varchar', 'constraint' => '250', 'null' => TRUE, 'default' => NULL),
    'member_access' => array('type' => 'varchar', 'constraint' => '250', 'default' => 'all')

ee()->dbforge->add_key('file_id', TRUE);



$fields = array(
    'file_id'   => array('type' => 'int', 'constraint' => '10', 'unsigned' => TRUE),
    'entry_id'  => array('type' => 'int', 'constraint' => '10', 'unsigned' => TRUE)

ee()->dbforge->add_key('file_id', TRUE);
ee()->dbforge->add_key('entry_id', TRUE);


Lastly, we ensure that any saved publish layouts have our new tab data added to the saved layout via the layout library’s add_layout_tabs() function. Once all of this has completed, the function should return TRUE:

    ee()->layout->add_layout_tabs($this->tabs(), 'download');

    return TRUE;

Uninstall Function

The uninstall function in the Control Panel class for the module should be pretty standard for every module. It clears out all mention of the module in the standard ExpressionEngine database tables. If the module created tables for its own usage, then those will also be deleted in this function:

function uninstall()

    $query = ee()->db->get_where('modules', array('module_name' => 'Download'));

    ee()->db->where('module_id', $query->row('module_id'));

    ee()->db->where('module_name', 'Download');

    ee()->db->where('class', 'Download');


    // Required if your module includes fields on the publish page
    ee()->layout->delete_layout_tabs($this->tabs(), 'download');

    return TRUE;

Note the use of the layout library’s delete_layout_tabs() function to remove our tab from saved layouts.

Update Function

The update function provides you with a mechanism for updating the database automatically if you find you need new fields in the future. The function is required, even if you don’t need it yet. At a minimum, your update function should look like:

function update($current = '')
    return FALSE;

Our Download module is in its first iteration, so there’s really nothing to update. In this case, the function simply returns FALSE. If the update function returns TRUE, the version number stored in exp_modules will automatically be updated as well, making sure the update function only runs when it needs to.

Tab Function

On install and uninstall, we called the tabs() function when updating custom publish page layouts. This function returns a multidimensional associative array. The top level key is the name of the tab. Within that array, each field name acts is a key, and contains the default display states to be added to any existing custom layouts:

function tabs()
    $tabs['download'] = array(
        'download_field_ids'    => array(
            'visible'   => 'true',
            'collapse'  => 'false',
            'htmlbuttons'   => 'false',
            'width'     => '100%'

    return $tabs;

The Language File (download_lang.php)

The Language file contains no classes, simply an array named $lang, which is used along with the Language class to display text on a page in whatever language is selected in the user’s account settings. There are two required lines in the language file for each module, which allows the name and description of the module to be viewable on the MODULES page. In addition, the Download module requires a number of key => value pairs for use in the control panel as well as frontend error display (see the file).

The Control Panel file (

The Control Panel file for a module includes a class with a name that is a combination of the package’s name with _mcp tacked on the end. So, for our Download module, we will create a class called Download_mcp. There are no required class variables. Because the module requires multiple pages, a link to the ‘Add Files’ page is added to the fourth level navigation using the set_right_nav function:

function __construct()
        'add_download'  => BASE.AMP.'C=addons_modules'.AMP.'M=show_module_cp'

Module’s Control Panel Homepage

By default, if you do not specify a method in your url, ExpressionEngine will attempt to load an index function, thus we make the index() our module homepage. This page is fairly typical: a list of all existing download records with the file name, assigned title, allowed member groups, and a checkbox to allow editing/deleting of records. Let’s start with a simplified example, one where we leave the javascript embellishments out for now.

The function starts by loading the libraries and helpers required later, and defines some initial variables that will be used in the view file. Also note the use of the CP set_variable method to set our page title:

function index()

    ee()->view->cp_page_title = lang('download_module_name');

    $vars['action_url'] = 'C=addons_modules'.AMP.'M=show_module_cp'.AMP.'module=download'.AMP.'method=edit_downloads';
    $vars['form_hidden'] = NULL;
    $vars['files'] = array();

    $vars['options'] = array(
        'edit'  => lang('edit_selected'),
        'delete'    => lang('delete_selected')

Because we may need to paginate our list of files, we need to check for the row number indicator and then use this in our main query. Make sure to use the active record class when constructing your queries. This will enable your queries to work as support for more database types are added:

if ( ! $rownum = ee()->input->get_post('rownum'))
    $rownum = 0;

ee()->db->order_by("file_id", "desc");
$query = ee()->db->get('download_files', $this->perpage, $rownum);

We then loop through the query results and format a $vars['files'] array for easy use in our view file:

// get all member groups for the dropdown list
$member_groups = ee()->member_model->get_member_groups();

foreach($member_groups->result() as $group)
    $member_group[$group->group_id] = $group->group_title;

foreach($query->result_array() as $row)
    $vars['files'][$row['file_id']]['entry_title'] = $row['file_title'];
    $vars['files'][$row['file_id']]['edit_link'] = BASE.AMP.'C=addons_modules'.AMP
    $vars['files'][$row['file_id']]['dir_id'] = $row['dir_id'];
    $vars['files'][$row['file_id']]['file_name'] = $row['file_name'];
    $vars['files'][$row['file_id']]['file_title'] = $row['file_title'];

    $access = '';
    $member_access = explode('|', $row['member_access']);

    foreach ($member_access as $group_id)
        $access .= (isset($member_group[$group_id])) ? $member_group[$group_id] : $group_id;
        $access .= ', ';

    $vars['files'][$row['file_id']]['member_access'] = rtrim($access, ', ');

    // Toggle checkbox
    $vars['files'][$row['file_id']]['toggle'] = array(
        'name'      => 'toggle[]',
        'id'        => 'edit_box_'.$row['file_id'],
        'value'     => $row['file_id'],
        'class'     =>'toggle'

All our variables aside from pagination are now in place. We need to check our total number of files, configure our pagination, and then load our view file. There’s no need to create a separate function for our pagination configuration. However, it makes this example a bit more simple and reduces redundancy if you have multiple functions that you need to paginate:

    //  Check for pagination
    $total = ee()->db->count_all('download_files');

    // Pass the relevant data to the paginate class so it can display the "next page" links
    $p_config = $this->pagination_config('index', $total);


    $vars['pagination'] = ee()->pagination->create_links();

    return ee()->load->view('index', $vars, TRUE);

Here’s the abstracted pagination_config method used by the above:

function pagination_config($method, $total_rows)
    // Pass the relevant data to the paginate class
    $config['base_url'] = BASE.AMP.'C=addons_modules'.AMP.'M=show_module_cp'.AMP.'module=download'.AMP.'method='.$method;
    $config['total_rows'] = $total_rows;
    $config['per_page'] = $this->perpage;
    $config['page_query_string'] = TRUE;
    $config['query_string_segment'] = 'rownum';
    $config['full_tag_open'] = '<p id="paginationLinks">';
    $config['full_tag_close'] = '</p>';
    $config['prev_link'] = '<img src="'.ee()->cp->cp_theme_url.'images/pagination_prev_button.gif" width="13" height="13" alt="<" />';
    $config['next_link'] = '<img src="'.ee()->cp->cp_theme_url.'images/pagination_next_button.gif" width="13" height="13" alt=">" />';
    $config['first_link'] = '<img src="'.ee()->cp->cp_theme_url.'images/pagination_first_button.gif" width="13" height="13" alt="< <" />';
    $config['last_link'] = '<img src="'.ee()->cp->cp_theme_url.'images/pagination_last_button.gif" width="13" height="13" alt="> >" />';

    return $config;


While it is preferable that your module work for users who disable javascript, you may well want to provide increased functionality for the majority of users who don’t. ExpressionEngine 2.x includes both its own JavaScript library as well as the The jQuery JavaScript library, enabling developers to easily include JavaScript enhancements. In the final version of our Download modules index function, there is the ability to ‘toggle all’ checkboxes as well as an enhanced table presentation that allows ajax sorting of columns as well as pagination.

Adding ‘toggle all’ functionality is a simple matter:

            $("input.toggle").each(function() {
                this.checked = true;
        }, function (){
            var checked_status = this.checked;
            $("input.toggle").each(function() {
                this.checked = false;

In order to add the sortable ajax paginated table, we make use of the DataTables jQuery plugin. When using a plugin, it must first be loaded:

ee()->cp->add_js_script(array('plugin' => 'dataTables'));

The details of how to use this particular plugin can be seen in the attached module files, and in this case, the bulk of the coding is again abstracted to the ajax_filters() function:

ee()->javascript->output($this->ajax_filters('edit_items_ajax_filter', 4));

In order to display the javascript, the last step is to compile it:


The View files

Given the complexity of our backend pages, we use view files to handle the display and formatting as seen in the index() above:

return ee()->load->view('index', $vars, TRUE);

This would return the index.php view page, located in a views folder:

<?php if (count($files) > 0): ?>
<?=form_open($action_url, '', $form_hidden)?>

        form_checkbox('select_all', 'true', FALSE, 'class="toggle_all" id="select_all"'));

    foreach($files as $file)
                '<a href="'.$file['edit_link'].'">'.$file['file_name'].'</a>',

echo $this->table->generate();


<div class="tableFooter">
    <div class="tableSubmit">
        <?=form_submit(array('name' => 'submit', 'value' => lang('submit'), 'class' => 'submit')).NBS.NBS.form_dropdown('action', $options)?>

    <span class="js_hide"><?=$pagination?></span>
    <span class="pagination" id="filter_pagination"></span>


<?php else: ?>
<?php endif; ?>

It is recommended that in view pages only, you use the PHP’s alternate syntax in your views, as it makes them easier to read and limits the amount of php. If this is not supported by your server, ExpressionEngine will automatically rewrite the tags.

This is a fairly complex page, but it is easy to change the layout and style, even for someone who isn’t a PHP pro. The view uses the table class to generate tables, though pure html would work just as well. It also uses the form helper to create certain form elements. While not required, the form helper is strongly recommended. All that is needed to make this page work is for the function loading it to pass an array with all of the variables used by the view.

The Tab File (

Because our module adds a tab to the publish page, it will need to include the optional Tab file:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Download_tab {

The tab class must include 4 required functions: publish_tabs(), validate_publish(), publish_data_db() and publish_data_delete_db().

Publish Tabs Function

This required function allows you to create the fields on the publish page. In this case, there is only a single multiselect field named download_field_ids. The field is populated by the existing file records:

function publish_tabs($channel_id, $entry_id = '')
    $settings = array();
    $selected = array();
    $existing_files = array();

    $query = ee()->db->get('download_files');

    foreach ($query->result() as $row)
        $existing_files[$row->file_id] = $row->file_name;

    if ($entry_id != '')
        $query = ee()->db->get_where('download_posts', array('entry_id' => $entry_id));

        foreach ($query->result() as $row)
            $selected[] = $row->file_id;

    $id_instructions = lang('id_field_instructions');

    // Load the module lang file for the field label

    $settings[] = array(
            'field_id'      => 'download_field_ids',
            'field_label'       => lang('download_files'),
            'field_required'    => 'n',
            'field_data'        => $selected,
            'field_list_items'  => $existing_files,
            'field_fmt'     => '',
            'field_instructions'    => $id_instructions,
            'field_show_fmt'    => 'n',
            'field_pre_populate'    => 'n',
            'field_text_direction'  => 'ltr',
            'field_type'        => 'multi_select'

    return $settings;

Publish Validation Function

The validation function allows you to validate the data for your publish page fields prior to any publish data being entered or updated. It has one parameter, $params, which is an associative array of all the data available. The download module doesn’t require any validation, so can simply return FALSE.

Publish Data Function

The publish data function allows you to manipulate the submitted data after the main data entry has occurred. Typically this will involve creating a record in the module’s database, as is the case here. The single parameter is an associative array, the top level arrays consisting of: meta, data, mod_data, and entry_id:

function publish_data_db($params)
    // Remove existing
    ee()->db->where('entry_id', $params['entry_id']);

    if (isset($params['mod_data']['download_field_ids']) &&
        is_array($params['mod_data']['download_field_ids']) &&
        count($params['mod_data']['download_field_ids']) > 0)
        foreach ($params['mod_data']['download_field_ids'] as $val)
            $data = array(
                'entry_id' => $params['entry_id'],
                'file_id' => $val

        ee()->db->insert('download_posts', $data);

Publish Data Delete Function

This function is called when entries are deleted, and allows you to synchronize your module tables and make any other adjustments necessary when an entry that may be associated with module data is deleted. In the case of the Download module, we need to remove any records for deleted entry ids from our exp_download_posts table:

function publish_data_delete_db($params)
    // Remove existing
    ee()->db->where_in('entry_id', $params['entry_ids']);

The Core Module file (

In ExpressionEngine, a typical module or plugin tag has an appearance similar to this:


Our Download module’s main tag is a tag pair, designed to be nested inside a channel entries tag. The tag has a required parameter entry_id, and an optional limit parameter. Thus all download images associated with a given entry can be displayed along with the entry’s standard data:

{exp:channel:entries limit="10"}
    {exp:download:entries entry_id="{entry_id}"}
        {file_title} - {file_download}

The Core Module file is called by any tag that designates the ‘download’ module. The file consists of a class using the same name of the module and containing at least one class variable, $return_data, which will contain the module’s outputted content and is retrieved by the Template parser after the module is done processing. The basic class at this point looks like:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Download {

    var $return_data    = '';


Next, we need to add a function that outputs our download data. Note that according to our tag, this function is expected to be named entries:

function entries()
    if (($entry_id = ee()->TMPL->fetch_param('entry_id')) === FALSE) return;

    $limit  = ( ! isset($params['limit']) OR ! is_numeric($params['limit'])) ? 100 : $params['limit'];

    ee()->db->where('entry_id', $entry_id);
    ee()->db->join('download_posts', 'download_files.file_id = download_posts.file_id', 'right');

    $query = ee()->db->get();

    if ($query->num_rows() == 0)
        return ee()->TMPL->no_results();

The function first checks for the existence of the required entry_id, queries to find all download records for that id, and returns the no_results function if no records exist. If there are records to parse, the Typography class is initialized and the data parsed out and returned.

The Template class, offers two general approaches to parsing out the data. Here we use the simple parse_variables method, where we simply need to pass a multidimensional associative array where our tags are the keys and the values our replacement data:

    //  Instantiate Typography class

    ee()->typography->parse_images = TRUE;
    ee()->typography->allow_headings = FALSE;

    $base_url = ee()->functions->fetch_site_index(0, 0).QUERY_MARKER.'ACT='.ee()->functions->fetch_action_id('Download', 'force_download');

    foreach ($query->result_array() as $id => $row)
        $variables[] = array(
            'file_title' => $row['file_title'],
            'file_link' => '{filedir_'.$row['dir_id'].'}',
            'file_download' => $base_url.AMP.'id='.$row['file_id']


    return ee()->TMPL->parse_variables(ee()->TMPL->tagdata, $variables);

Lastly, this module needs to force downloads and obscure image paths, and it does so by use of the action id. During installation, we added the function force_download into the exp_actions table. Thus we need to include that function in our module. The method should pull the file_id as get data, look up the correct path, and deliver that file with appropriate headers to users who meet the access requirements:

function force_download()
    $file_id = ee()->input->get('id');

    if ($file_id === FALSE)
        return ee()->output->show_user_error('general', lang('invalid_download'));

    $group_id = ee()->session->userdata['group_id'];


    ee()->db->select('file_name, file_title, member_access, server_path, url');
    ee()->db->join('upload_prefs', ' = download_files.dir_id');
    ee()->db->where('file_id', $file_id);

    $query = ee()->db->get();

    if ($query->num_rows() > 0)
        $row = $query->row();

        $allowed = explode('|', $row->member_access);

        if ( ! in_array('all', $allowed) && ! in_array($group_id, $allowed))
            return ee()->output->show_user_error('general', lang('no_permission'));

        $file_name = $row->file_name;
        $file_path = $row->server_path.$file_name;

        $data = file_get_contents($file_path); // Read the file's contents

        force_download($file_name, $data);