Adding custom fields to core components using a plugin

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Have you ever wished that there was an extra phone number field in com_contact or needed an extra field for articles in com_content? Joomla! provides a straight-forward way of integrating new fields with core components such as these. All it takes to achieve this is a simple content plugin and a layout override in your template.

This article shows how to add an extra field to a core component using the example of adding an additional email address to contacts in com_contact. If you need to add custom fields to com_content for your Joomla articles, simply change any references from "contact" to "content" in the code below. And notice that com_content use "attribs" and not "params" for the fields value as well as for the override.

Adding a Custom Field[edit]

It is recommended that you first read Creating a Plugin for Joomla! for details on how to create and install a plugin, which is not covered here.

To add a field to a system component you need to create a content plugin which picks up the onContentPrepareForm event and inserts its own fields into the given JForm. The following code is for Joomla 3.1 and later.

// no direct access
defined ('_JEXEC') or die;
class plgContentExample extends JPlugin
	 * Load the language file on instantiation.
	 * Note this is only available in Joomla 3.1 and higher.
	 * If you want to support 3.0 series you must override the constructor
	 * @var boolean
	 * @since <your version>
	protected $autoloadLanguage = true;

	 * Prepare form and add my field.
	 * @param   JForm  $form  The form to be altered.
	 * @param   mixed  $data  The associated data for the form.
	 * @return  boolean
	 * @since   <your version>
	function onContentPrepareForm($form, $data)
		$app    = JFactory::getApplication();
		$option = $app->input->get('option');

			case 'com_contact' :
				if ($app->isClient('administrator'))
					JForm::addFormPath(__DIR__ . '/forms');
					$form->loadFile('contact', false);

				return true;

		return true;

Enabling Front End Editing of Custom Fields[edit]

Enabling Frontend editing for your new custom fields is pretty easy. To add the fields to the frontend content edit form, simply add this block of code:

case 'com_contact':
	if ($app->isClient('site'))
		JForm::addFormPath(__DIR__ . '/forms');
		$form->loadFile('contact', false);
	return true;

Add that immediately below the existing instance of it.

Once you've got that done, create a template override for the content form edit.php file. If you're creating a set of custom fields for com_contact, you would copy /components/com_contact/views/form/tmpl/edit.php to /templates/your-template-name/html/com_contact/form/edit.php

Inside your layout override, add your new fields in the form where you want them to appear (e.g., below the title, below the description), making sure that the field names match the XML file from your plugin (you'll create this next).

<?php // Checking if this is an existing item or not ?>
<?php if ($this->item->id) : ?>
  <?php // If it is an existing item, get the attribs part of the existing record ?>
  <?php $attribs = json_decode($this->item->attribs); ?>
  <?php // Set the value of the custom field to what is already saved. ?>
  <?php // Duplicate for the number of fields you need, changing the field_name as needed. ?>
  <?php echo $this->form->setValue('field_name', 'attribs', $attribs->field_name); ?>
<?php endif; ?>
<?php // This line needs added to the file right where you want to display it. So, if you want it to show right after the description field, find the description field and place this right after it. Duplicate for the number of fields you need, changing the field_name as needed. ?>
<?php // Now we display the field. If we are editing an existing item, the previously saved data will be populated already ?>
<?php echo $this->form->renderField('field_name', 'attribs'); ?>

With that done, your fields will now appear and be stored via frontend editing.

The additional fields are loaded from the file forms/contact.xml in the plugin directory. It's important that these fields are in a fields element with the name property set to "params". If you don't set this property name, the fields will appear in the admin site but the values will not be saved. Note: In com_content your field must be named "<fields name="attribs">" otherwise the fields will appear in the admin site but the values will not be saved.

In this case we are adding a field for a label to describe the email field in the public website and a second field for the value of the email address.

<?xml version="1.0" encoding="UTF-8"?>
	<fields name="params">
		<fieldset name="params" label="PLG_CONTENT_EXAMPLE_FIELDSET_LABEL">

Finally we need a language file so that the parameters are presented nicely in the admin site and are translatable into different languages. This file needs to be called something like en-GB.plg_content_example.ini.

PLG_CONTENT_EXAMPLE_CONTACT_EMAIL2="Additional email address"

That's it for adding the field to com_contact. If you install this plugin, you'll have an additional tab in the contact editing form called "Additional Information" with the new fields included. If you fill in the new label and email address fields for a contact, you'll see that com_contact will store and retrieve the information for you.

The same plugin can be used to add more fields to different components; just add the relevant code into the onContentPrepareForm function and create the appropriate XML form files.

Displaying the Custom Field[edit]

To display the custom field you need to create a layout override for the relevant component in your template. For more details on creating templates see Creating a basic Joomla! template. For details on layout overrides, see Understanding Output Overrides.

Copy the file <Joomla>/components/com_contact/views/contact/tmpl/default.php to <template>/html/com_contact/contact/default.php, creating the folders in your template as necessary. We're going to edit this file to include the additional information. The com_contact component will automatically load the additional fields for us and load it into a variable called $this->params. All we need to do is check that the data is set and, if so, display it.

To display the field, find the location in <template>/html/com_contact/contact/default.php that corresponds to where you'd like the additional email address to be displayed and add the following code:

<?php if ($this->params->get('contact_emaillabel2', false)) : ?>
		<span class="contact-additionalemail"><?php echo $this->params->get('contact_emaillabel2'); ?>:&emsp;<a href="mailto:<?php echo $this->params->get('contact_email2'); ?>"><?php echo $this->params->get('contact_email2'); ?></a><br/></span>
<?php endif; ?>

If you add this code and install your template, you will now have the custom field displaying in your public Website.