J3.x

Développement d'un composant MVC - Ajout de tags

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< J3.x:Developing an MVC Component
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Joomla! 
3.x
Didacticiel
Développement d'un composant MVC


Ceci est une série qui regroupe plusieurs articles pour devenir un didacticiel sur la façon de développer un Composant pour Joomla! Joomla 3.x suivant le principe Modèle-Vue-Contrôleur.

Commencez avec l'introduction, et naviguez dans les articles de cette série soit à l'aide des boutons de navigation en bas des articles, soit grâce au menu de droite : Les articles de cette série.



Ce didacticiel fait partie de la série de didacticiels sur le Développement d'un Composant MVC pour Joomla! 3.x. Vous êtes invité à lire les articles précédents de cette série avant de lire celui-ci.

In this step we add tags to our helloworld component. A video accompanying this step is available at Adding Tags.

Introduction

Tags give an alternative view which enables visitors to a website to explore the content by subject matter, via the tags which have been assigned to items, rather than through the website menu structure. Joomla allows you to add tags to articles, newsfeeds, categories and contacts, amongst other items, and while an item may belong to at most one category, an item may have multiple tags. In this step we extend this functionality to our helloworld records and categories.

Joomla has designed the tags functionality on top of the UCM (Unified Content Model) tables in the database. The UCM was a concept which was only partly developed in Joomla, and has an uncertain future. For the various types of content in Joomla – articles, contacts, newsfeeds, etc – it aimed at storing common information in a common database table (the ucm_content table, together with the associated ucm_base table), and only the fields which were special to that content type in a separate table.

Joomla Tags E-R diagram

The Joomla tags functionality is built on top of UCM, as shown in the entity-relationship diagram, with the contentitem_tag_map table implementing the many-many relationship between tags and items of content. For us this means that we need to have key fields from the helloworld records and categories copied into the ucm_content table, and we enable this by specifying configuration data in the content_types table, similar to what we did in the last step Adding Versioning.

Joomla tags uses the same Observer pattern as Joomla versioning: whenever a record is stored in the JTable class, the onBeforeStore, onAfterStore and onBeforeDelete events are picked up by the tags code, and when a tag is first set on a record it copies the fields from the original record into the ucm_content table, using the field mapping defined in the content_types configuration data, and also writes an abridged record into the ucm_base table. It then writes a contentitem_tag_map record which links to the ucm_content and tags records, to store the fact that tag x is specified against content item y.

Approche

Some details of how to include tags functionality in an extension are given in Using Tags in an Extension. In our database files we add the configuration data to the helloworld content_types records which will enable the Joomla tags functionality to copy the important fields from our helloworld records and helloworld category records to the ucm_content records.

We add the code to our helloworld table class to get the tags observer to subscribe to events associated with our helloworld table class. Adding this in the constructor of our helloworld table class means that this will apply to both the back end and front end, as both use the same helloworld table code.

We add a standard Joomla tags field to our admin form for editing a helloworld record, and to our front end form for creating a helloworld record. The tags field has 2 modes of operation, see Tag form field type:

  1. nested: the tags are presented as a fixed list from which the user can select one or more (assuming the field option multiple="true" is set). Tags are implemented as a tree in a Nested Table structure, so in the presentation within the tags field subtags are indented, in the same way as submenus and subcategories are indented in those admin forms.
  2. ajax (default): the tags are presented as a list, but as a list of nested table paths, rather than having subtags indented. In addition the user may enter free text: when a number of characters are entered Joomla executes an Ajax request to the server to find tags matching the entered text. If no matching tags are found the user can create a new tag on the fly this way, except if the option custom="deny" is added to the tags field.

We use the ajax mode on the admin form, and the nested mode on the front end form.

With regard to presentation of the tags which a record has, on the back end admin edit form we want to show what tags are already present by pre-populating the tags field, so within our model code we get this data from the database. We'll not display the tags in the admin helloworlds form.

On the front end, we'll display the tags associated with a helloworld record in the Hello World menuitem, and for this we'll use a standard Joomla layout.

Base de données

In our database update file we add into the content_types records the table and field mapping information which will enable those field values to be copied into the ucm_content table. For the category records we just follow the example of Joomla core components. For the helloworld records we need to consider what tag-related data might be shown on other web pages, for example, if the administrator created a menuitem pointing to one of the Tags menu item types. Such pages will have links to the helloworld records, so fields such as alias and language which are used in the construction of the URLs should be included. The "special" field mappings aren't currently used, so it's safe to omit those.

Administrators can set up front end Menu Item Types (of type Tags) which display links to items which have specific tags. In the case where an item is a helloworld record or a helloworld category record Joomla will look for a route helper method to be specified in the ucm_content router field, so we update the records to contain values for these. We define these methods below in the Site Route Helper section.

admin/sql/updates/mysql/0.0.28.sql

UPDATE `#__content_types` SET
`table` = '{"special":{"dbtable":"#__helloworld","key":"id","type":"Helloworld","prefix":"HelloworldTable","config":"array()"},
"common":{"dbtable":"#__ucm_content","key":"ucm_id","type":"Corecontent","prefix":"JTable","config":"array()"}}',
`field_mappings` = 
'{"common": {
    "core_content_item_id": "id",
    "core_title": "greeting",
    "core_state": "published",
    "core_alias": "alias",
    "core_language":"language", 
    "core_created_time": "created",
    "core_body": "description",
    "core_catid": "catid"
  }}',
`router` = 'HelloworldHelperRoute::getHelloworldRoute'
WHERE `type_alias` = 'com_helloworld.helloworld';

UPDATE `#__content_types` SET
`table` = '{"special":{"dbtable":"#__categories","key":"id","type":"Category","prefix":"JTable","config":"array()"},
"common":{"dbtable":"#__ucm_content","key":"ucm_id","type":"Corecontent","prefix":"JTable","config":"array()"}}',
`field_mappings` = 
'{"common": {
	"core_content_item_id":"id",
	"core_title":"title",
	"core_state":"published",
	"core_alias":"alias",
	"core_created_time":"created_time",
	"core_modified_time":"modified_time",
	"core_body":"description", 
	"core_hits":"hits",
	"core_publish_up":"null",
	"core_publish_down":"null",
	"core_access":"access", 
	"core_params":"params", 
	"core_featured":"null", 
	"core_metadata":"metadata", 
	"core_language":"language", 
	"core_images":"null", 
	"core_urls":"null", 
	"core_version":"version",
	"core_ordering":"null", 
	"core_metakey":"metakey", 
	"core_metadesc":"metadesc", 
	"core_catid":"parent_id", 
	"core_xreference":"null", 
	"asset_id":"asset_id"}, 
  "special":{
    "parent_id":"parent_id",
	"lft":"lft",
	"rgt":"rgt",
	"level":"level",
	"path":"path",
	"extension":"extension",
	"note":"note"}}',
`router` = 'HelloworldHelperRoute::getCategoryRoute'
WHERE `type_alias` = 'com_helloworld.category';

admin/sql/install.mysql.utf8.sql

DROP TABLE IF EXISTS `#__helloworld`;

CREATE TABLE `#__helloworld` (
	`id`       INT(11)     NOT NULL AUTO_INCREMENT,
	`asset_id` INT(10)     NOT NULL DEFAULT '0',
	`created`  DATETIME    NOT NULL DEFAULT '0000-00-00 00:00:00',
	`created_by`  INT(10) UNSIGNED NOT NULL DEFAULT '0',
	`checked_out` INT(10) NOT NULL DEFAULT '0',
	`checked_out_time` DATETIME NOT NULL DEFAULT '0000-00-00 00:00:00',
	`greeting` VARCHAR(25) NOT NULL,
	`description` VARCHAR(4000) NOT NULL DEFAULT '',
	`alias`  VARCHAR(40)  NOT NULL DEFAULT '',
    `language`  CHAR(7)  NOT NULL DEFAULT '*',
	`parent_id`	int(10)    NOT NULL DEFAULT '1',
	`level`	int(10)    NOT NULL DEFAULT '0',
	`path`	VARCHAR(400)    NOT NULL DEFAULT '',
	`lft`	int(11)    NOT NULL DEFAULT '0',
	`rgt`	int(11)    NOT NULL DEFAULT '0',
	`published` tinyint(4) NOT NULL DEFAULT '1',
	`catid`	    int(11)    NOT NULL DEFAULT '0',
	`params`   VARCHAR(1024) NOT NULL DEFAULT '',
	`image`   VARCHAR(1024) NOT NULL DEFAULT '',
	`latitude` DECIMAL(9,7) NOT NULL DEFAULT 0.0,
	`longitude` DECIMAL(10,7) NOT NULL DEFAULT 0.0,
	PRIMARY KEY (`id`)
)
	ENGINE =MyISAM
	AUTO_INCREMENT =0
	DEFAULT CHARSET =utf8;

CREATE UNIQUE INDEX `aliasindex` ON `#__helloworld` (`alias`, `catid`);

INSERT INTO `#__helloworld` (`greeting`,`alias`,`language`, `parent_id`, `level`, `path`, `lft`, `rgt`) VALUES
('helloworld root','helloworld-root-alias','en-GB', 0, 0, '', 0, 5),
('Hello World!','hello-world','en-GB', 1, 1, 'hello-world', 1, 2),
('Goodbye World!','goodbye-world','en-GB', 1, 1, 'goodbye-world', 3, 4);

INSERT INTO `#__content_types` (`type_title`, `type_alias`, `content_history_options`, `table`, `field_mappings`, `router`) 
VALUES
('Helloworld', 'com_helloworld.helloworld', 
'{"formFile":"administrator\\/components\\/com_helloworld\\/models\\/forms\\/helloworld.xml", 
"hideFields":["asset_id","checked_out","checked_out_time","version","lft","rgt","level","path"], 
"ignoreChanges":["checked_out", "checked_out_time", "path"],
"convertToInt":[], 
"displayLookup":[
{"sourceColumn":"created_by","targetTable":"#__users","targetColumn":"id","displayColumn":"name"},
{"sourceColumn":"parent_id","targetTable":"#__helloworld","targetColumn":"id","displayColumn":"greeting"},
{"sourceColumn":"catid","targetTable":"#__categories","targetColumn":"id","displayColumn":"title"}]}',
'{"special":{"dbtable":"#__helloworld","key":"id","type":"Helloworld","prefix":"HelloworldTable","config":"array()"},
"common":{"dbtable":"#__ucm_content","key":"ucm_id","type":"Corecontent","prefix":"JTable","config":"array()"}}',
'{"common": {
    "core_content_item_id": "id",
    "core_title": "greeting",
    "core_state": "published",
    "core_alias": "alias",
    "core_language":"language", 
    "core_created_time": "created",
    "core_body": "description",
    "core_catid": "catid"
  }}',
'HelloworldHelperRoute::getHelloworldRoute'),
('Helloworld Category', 'com_helloworld.category',
'{"formFile":"administrator\\/components\\/com_categories\\/models\\/forms\\/category.xml", 
"hideFields":["asset_id","checked_out","checked_out_time","version","lft","rgt","level","path","extension"], 
"ignoreChanges":["modified_user_id", "modified_time", "checked_out", "checked_out_time", "version", "hits", "path"],
"convertToInt":["publish_up", "publish_down"], 
"displayLookup":[
{"sourceColumn":"created_user_id","targetTable":"#__users","targetColumn":"id","displayColumn":"name"},
{"sourceColumn":"access","targetTable":"#__viewlevels","targetColumn":"id","displayColumn":"title"},
{"sourceColumn":"modified_user_id","targetTable":"#__users","targetColumn":"id","displayColumn":"name"},
{"sourceColumn":"parent_id","targetTable":"#__categories","targetColumn":"id","displayColumn":"title"}]}',
'{"special":{"dbtable":"#__categories","key":"id","type":"Category","prefix":"JTable","config":"array()"},
"common":{"dbtable":"#__ucm_content","key":"ucm_id","type":"Corecontent","prefix":"JTable","config":"array()"}}',
'{"common": {
	"core_content_item_id":"id",
	"core_title":"title",
	"core_state":"published",
	"core_alias":"alias",
	"core_created_time":"created_time",
	"core_modified_time":"modified_time",
	"core_body":"description", 
	"core_hits":"hits",
	"core_publish_up":"null",
	"core_publish_down":"null",
	"core_access":"access", 
	"core_params":"params", 
	"core_featured":"null", 
	"core_metadata":"metadata", 
	"core_language":"language", 
	"core_images":"null", 
	"core_urls":"null", 
	"core_version":"version",
	"core_ordering":"null", 
	"core_metakey":"metakey", 
	"core_metadesc":"metadesc", 
	"core_catid":"parent_id", 
	"core_xreference":"null", 
	"asset_id":"asset_id"}, 
  "special":{
    "parent_id":"parent_id",
	"lft":"lft",
	"rgt":"rgt",
	"level":"level",
	"path":"path",
	"extension":"extension",
	"note":"note"}}',
'HelloworldHelperRoute::getCategoryRoute');

In our uninstall sql script we need to remove any helloworld records which have been copied into the ucm_base and ucm_content tables, and also remove any links to helloworld records in the tag link table contentitem_tag_map.

admin/sql/uninstall.mysql.utf8.sql

DROP TABLE IF EXISTS `#__helloworld`;
DELETE FROM `#__ucm_history` WHERE ucm_type_id in 
	(select type_id from `#__content_types` where type_alias in ('com_helloworld.helloworld','com_helloworld.category'));
DELETE FROM `#__ucm_base` WHERE ucm_type_id in 
	(select type_id from `#__content_types` WHERE type_alias in ('com_helloworld.helloworld','com_helloworld.category'));
DELETE FROM `#__ucm_content` WHERE core_type_alias in ('com_helloworld.helloworld','com_helloworld.category');
DELETE FROM `#__contentitem_tag_map`WHERE type_alias in ('com_helloworld.helloworld','com_helloworld.category');
DELETE FROM `#__content_types` WHERE type_alias in ('com_helloworld.helloworld','com_helloworld.category');

Setup Tags Observer

In the Adding Versioning step we used the JObserverMapper::addObserverClassToClass() function to set up the ContentHistory observer. In this step we use the alternative mechanism, using JTableObserverTags::createObserver() to set up the Tags observer. We call this in our helloworld table constructor, ensuring that it's called after the parent constructor.

admin/tables/helloworld.php

<?php
/**
 * @package     Joomla.Administrator
 * @subpackage  com_helloworld
 *
 * @copyright   Copyright (C) 2005 - 2015 Open Source Matters, Inc. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */
// No direct access
defined('_JEXEC') or die('Restricted access');

/**
 * Hello Table class
 *
 * @since  0.0.1
 */
class HelloWorldTableHelloWorld extends JTableNested
{
	/**
	 * Constructor
	 *
	 * @param   JDatabaseDriver  &$db  A database connector object
	 */
	function __construct(&$db)
	{
		JObserverMapper::addObserverClassToClass('JTableObserverContenthistory', 'HelloWorldTableHelloWorld', array('typeAlias' => 'com_helloworld.helloworld'));
		parent::__construct('#__helloworld', 'id', $db);
		JTableObserverTags::createObserver($this, array('typeAlias' => 'com_helloworld.helloworld'));
	}
	/**
	 * Overloaded bind function
	 *
	 * @param       array           named array
	 * @return      null|string     null is operation was satisfactory, otherwise returns an error
	 * @see JTable:bind
	 * @since 1.5
	 */
	public function bind($array, $ignore = '')
	{
		if (isset($array['params']) && is_array($array['params']))
		{
			// Convert the params field to a string.
			$parameter = new JRegistry;
			$parameter->loadArray($array['params']);
			$array['params'] = (string)$parameter;
		}
        
        if (isset($array['imageinfo']) && is_array($array['imageinfo']))
		{
			// Convert the imageinfo array to a string.
			$parameter = new JRegistry;
			$parameter->loadArray($array['imageinfo']);
			$array['image'] = (string)$parameter;
		}
        
        // Bind the rules.
		if (isset($array['rules']) && is_array($array['rules']))
		{
			$rules = new JAccessRules($array['rules']);
			$this->setRules($rules);
		}
        
		if (isset($array['parent_id']))
		{
			if (!isset($array['id']) || $array['id'] == 0)
			{   // new record
				$this->setLocation($array['parent_id'], 'last-child');
			}
			elseif (isset($array['helloworldordering']))
			{
				// when saving a record load() is called before bind() so the table instance will have properties which are the existing field values
				if ($this->parent_id == $array['parent_id'])
				{
					// If first is chosen make the item the first child of the selected parent.
					if ($array['helloworldordering'] == -1)
					{
						$this->setLocation($array['parent_id'], 'first-child');
					}
					// If last is chosen make it the last child of the selected parent.
					elseif ($array['helloworldordering'] == -2)
					{
						$this->setLocation($array['parent_id'], 'last-child');
					}
					// Don't try to put an item after itself. All other ones put after the selected item.
					elseif ($array['helloworldordering'] && $this->id != $array['helloworldordering'])
					{
						$this->setLocation($array['helloworldordering'], 'after');
					}
					// Just leave it where it is if no change is made.
					elseif ($array['helloworldordering'] && $this->id == $array['helloworldordering'])
					{
						unset($array['helloworldordering']);
					}
				}
				// Set the new parent id if parent id not matched and put in last position
				else
				{
					$this->setLocation($array['parent_id'], 'last-child');
				}
			}
		}

		return parent::bind($array, $ignore);
	}
    
    /**
	 * Method to compute the default name of the asset.
	 * The default name is in the form `table_name.id`
	 * where id is the value of the primary key of the table.
	 *
	 * @return	string
	 * @since	2.5
	 */
	protected function _getAssetName()
	{
		$k = $this->_tbl_key;
		return 'com_helloworld.helloworld.'.(int) $this->$k;
	}
	/**
	 * Method to return the title to use for the asset table.
	 *
	 * @return	string
	 * @since	2.5
	 */
	protected function _getAssetTitle()
	{
		return $this->greeting;
	}
	/**
	 * Method to get the asset-parent-id of the item
	 *
	 * @return	int
	 */
	protected function _getAssetParentId(JTable $table = NULL, $id = NULL)
	{
		// We will retrieve the parent-asset from the Asset-table
		$assetParent = JTable::getInstance('Asset');
		// Default: if no asset-parent can be found we take the global asset
		$assetParentId = $assetParent->getRootId();

		// Find the parent-asset
		if (($this->catid)&& !empty($this->catid))
		{
			// The item has a category as asset-parent
			$assetParent->loadByName('com_helloworld.category.' . (int) $this->catid);
		}
		else
		{
			// The item has the component as asset-parent
			$assetParent->loadByName('com_helloworld');
		}

		// Return the found asset-parent-id
		if ($assetParent->id)
		{
			$assetParentId=$assetParent->id;
		}
		return $assetParentId;
	}

	public function check()
	{
		$this->alias = trim($this->alias);
		if (empty($this->alias))
		{
			$this->alias = $this->greeting;
		}
		$this->alias = JFilterOutput::stringURLSafe($this->alias);
		return true;
	}

	public function delete($pk = null, $children = false)
	{
		return parent::delete($pk, $children);
	}
}

Admin Edit Form

In the admin edit form we add the standard Joomla Tags field, allowing the administrator to select multiple tags, and also to create a new tag on the fly.

We also add a Status field, which we set to 1 (published) by default. The reason for this is that our published field in the database has a default of 1, so that new helloworld records by default get a status of published. However, the equivalent field state in the ucm_content table is set to zero by default, signifying unpublished. In that case, if we used some of the Joomla functionality to display the items associated with a certain tag, then our helloworld record wouldn't appear, as Joomla shows only published items. When we include our status field in the form, then its value gets copied into the ucm_content record (based on our field mapping above), and so matching its value in the helloworld record.

admin/models/forms/helloworld.xml

<?xml version="1.0" encoding="utf-8"?>
<form
				addrulepath="/administrator/components/com_helloworld/models/rules"
>
	<fieldset
				name="details"
				label="COM_HELLOWORLD_HELLOWORLD_DETAILS"
	>
		<field
				name="id"
				type="hidden"
				/>
                <field
				name="greeting"
				type="text"
				label="COM_HELLOWORLD_HELLOWORLD_GREETING_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_GREETING_DESC"
				size="40"
				class="inputbox validate-greeting"
				validate="greeting"
				required="true"
				default=""
				/>
		<field 
				name="alias" 
				type="text" 
				label="JFIELD_ALIAS_LABEL"
				description="JFIELD_ALIAS_DESC"
				hint="JFIELD_ALIAS_PLACEHOLDER"
				size="40" 
				/>
        <field
				name="catid"
				type="category"
				extension="com_helloworld"
				class="inputbox"
				default=""
				label="COM_HELLOWORLD_HELLOWORLD_FIELD_CATID_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_FIELD_CATID_DESC"
				required="true"
		>
			<option value="0">JOPTION_SELECT_CATEGORY</option>
		</field>
		<field
				name="latitude"
				type="number"
				label="COM_HELLOWORLD_HELLOWORLD_FIELD_LATITUDE_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_FIELD_LATITUDE_DESC"
				min="-90.0"
				max="90.0"
				class="inputbox"
				required="true"
				default="0.0"
				/>
		<field
				name="longitude"
				type="number"
				label="COM_HELLOWORLD_HELLOWORLD_FIELD_LONGITUDE_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_FIELD_LONGITUDE_DESC"
				min="-180.0"
				max="180.0"
				class="inputbox"
				required="true"
				default="0.0"
				/>
		<field  
                name="language" 
        		type="contentlanguage" 
                label="JFIELD_LANGUAGE_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_FIELD_LANGUAGE_DESC"
		>
			<option value="*">JALL</option>
		</field>
		<field 	name="published" 
				type="list" 
				label="JSTATUS"
				description="JFIELD_PUBLISHED_DESC" 
				class="chzn-color-state"
				filter="intval" 	
				size="1" 
				default="1"
		>
			<option value="1">
				JPUBLISHED</option>
			<option value="0">
				JUNPUBLISHED</option>
		</field>
		<field 
				name="tags" 
				type="tag"
				label="JTAG" 
				description="JTAG_DESC"
				multiple="true"
		>
		</field>
		<field
				name="parent_id"
				type="helloworldparent"
				label="COM_HELLOWORLD_HELLOWORLD_FIELD_PARENT_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_FIELD_PARENT_DESC"
				default="1"
				filter="int">
		</field>
		<field
				name="helloworldordering"
				type="helloworldordering"
				label="JFIELD_ORDERING_LABEL"
				description="JFIELD_ORDERING_DESC"
				filter="int"
				size="1">
		</field>
		<field 	name="version_note"
				type="text"
				label="JGLOBAL_FIELD_VERSION_NOTE_LABEL"
				description="JGLOBAL_FIELD_VERSION_NOTE_DESC"
				class="inputbox" 
				size="45"
				labelclass="control-label">
		</field>
    </fieldset>
		<field 	name="description" 
				type="editor"
				label="COM_HELLOWORLD_HELLOWORLD_FIELD_DESCRIPTION_LABEL" 
				description="COM_HELLOWORLD_HELLOWORLD_FIELD_DESCRIPTION_DESC"
				filter="JComponentHelper::filterText" 
				buttons="true" 
		/>
	<fields name="imageinfo">
		<fieldset
				name="image-info"
				label="COM_HELLOWORLD_IMAGE_FIELDS"
		>
			<field
                name="image"
                type="media"
                preview="tooltip"
                label="COM_HELLOWORLD_HELLOWORLD_FIELD_IMAGE_LABEL"
                description="COM_HELLOWORLD_HELLOWORLD_FIELD_IMAGE_DESC" />
            <field name="alt"
                type="text"
                label="COM_HELLOWORLD_HELLOWORLD_FIELD_ALT_LABEL"
                description="COM_HELLOWORLD_HELLOWORLD_FIELD_ALT_DESC"
                size="30"/>
            <field name="caption"
                type="text"
                label="COM_HELLOWORLD_HELLOWORLD_FIELD_CAPTION_LABEL"
                description="COM_HELLOWORLD_HELLOWORLD_FIELD_CAPTION_DESC"
                size="30"/>
		</fieldset>
	</fields>
	<fields name="params">
		<fieldset
				name="params"
				label="JGLOBAL_FIELDSET_DISPLAY_OPTIONS"
		>
			<field
					name="show_category"
					type="list"
					label="COM_HELLOWORLD_HELLOWORLD_FIELD_SHOW_CATEGORY_LABEL"
					description="COM_HELLOWORLD_HELLOWORLD_FIELD_SHOW_CATEGORY_DESC"
					default=""
			>
				<option value="">JGLOBAL_USE_GLOBAL</option>
				<option value="0">JHIDE</option>
				<option value="1">JSHOW</option>
			</field>
		</fieldset>
	</fields>
	<fieldset
			name="accesscontrol"
			label="COM_HELLOWORLD_FIELDSET_RULES"
	>
    	<field
				name="asset_id"
				type="hidden"
				filter="unset"
				/>
    	<field
				name="rules"
				type="rules"
				label="COM_HELLOWORLD_FIELD_RULES_LABEL"
				filter="rules"
				validate="rules"
				class="inputbox"
				component="com_helloworld"
				section="message"
				/>
    </fieldset>
</form>

In the form we need to pre-populate the field with any existing tags set on that record, and we do that in the model getItem(). We only need to provide the ids of the tags already set. The titles of all the available tags and their corresponding ids will be obtained in the list of options for the html <select> statement, and the tags already present will get the selected attribute set based on matching their ids against the list of options. (Note that the html <select> statement gets converted by the Chosen javascript library, so you don't see it on the web page source).

admin/models/helloworld.php

<?php
/**
 * @package     Joomla.Administrator
 * @subpackage  com_helloworld
 *
 * @copyright   Copyright (C) 2005 - 2018 Open Source Matters, Inc. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */

// No direct access to this file
defined('_JEXEC') or die('Restricted access');

use Joomla\Registry\Registry;

/**
 * HelloWorld Model
 *
 * @since  0.0.1
 */
class HelloWorldModelHelloWorld extends JModelAdmin
{
    // JModelAdmin needs to know this for storing the associations 
	protected $associationsContext = 'com_helloworld.item';
    
	// Contenthistory needs to know this for restoring previous versions
	public $typeAlias = 'com_helloworld.helloworld';
	
	/**
	 * Method to override getItem to allow us to convert the JSON-encoded image information
	 * in the database record into an array for subsequent prefilling of the edit form
	 * We also use this method to prefill the tags and associations
	 */
	public function getItem($pk = null)
	{
		$item = parent::getItem($pk);
		if ($item AND property_exists($item, 'image'))
		{
			$registry = new Registry($item->image);
			$item->imageinfo = $registry->toArray();
		}

		if (!empty($item->id))
		{
			$tagsHelper = new JHelperTags;
			$item->tags = $tagsHelper->getTagIds($item->id, 'com_helloworld.helloworld');
		}
        
		// Load associated items
		if (JLanguageAssociations::isEnabled())
		{
			$item->associations = array();

			if ($item->id != null)
			{
				$associations = JLanguageAssociations::getAssociations('com_helloworld', '#__helloworld', 'com_helloworld.item', (int)$item->id);

				foreach ($associations as $tag => $association)
				{
					$item->associations[$tag] = $association->id;
				}
			}
		}
		return $item; 
	}
	
	/**
	 * Method to get a table object, load it if necessary.
	 *
	 * @param   string  $type    The table name. Optional.
	 * @param   string  $prefix  The class prefix. Optional.
	 * @param   array   $config  Configuration array for model. Optional.
	 *
	 * @return  JTable  A JTable object
	 *
	 * @since   1.6
	 */
	public function getTable($type = 'HelloWorld', $prefix = 'HelloWorldTable', $config = array())
	{
		return JTable::getInstance($type, $prefix, $config);
	}

	/**
	 * Method to get the record form.
	 *
	 * @param   array    $data      Data for the form.
	 * @param   boolean  $loadData  True if the form is to load its own data (default case), false if not.
	 *
	 * @return  mixed    A JForm object on success, false on failure
	 *
	 * @since   1.6
	 */
	public function getForm($data = array(), $loadData = true)
	{
		// Get the form.
		$form = $this->loadForm(
			'com_helloworld.helloworld',
			'helloworld',
			array(
				'control' => 'jform',
				'load_data' => $loadData
			)
		);

		if (empty($form))
		{
			return false;
		}

		return $form;
	}
    
    /**
	 * Method to preprocess the form to add the association fields dynamically
	 *
	 * @return     none
	 */
	protected function preprocessForm(JForm $form, $data, $group = 'helloworld')
	{
		// Association content items
		if (JLanguageAssociations::isEnabled())
		{
			$languages = JLanguageHelper::getContentLanguages(false, true, null, 'ordering', 'asc');

			if (count($languages) > 1)
			{
				$addform = new SimpleXMLElement('<form />');
				$fields = $addform->addChild('fields');
				$fields->addAttribute('name', 'associations');
				$fieldset = $fields->addChild('fieldset');
				$fieldset->addAttribute('name', 'item_associations');

				foreach ($languages as $language)
				{
					$field = $fieldset->addChild('field');
					$field->addAttribute('name', $language->lang_code);
					$field->addAttribute('type', 'modal_helloworld');
					$field->addAttribute('language', $language->lang_code);
					$field->addAttribute('label', $language->title);
					$field->addAttribute('translate_label', 'false');
				}

				$form->load($addform, false);
			}
		}
		parent::preprocessForm($form, $data, $group);
	}

	/**
	 * Method to get the script to be included on the form
	 *
	 * @return string	Script files
	 */
	public function getScript() 
	{
		return 'administrator/components/com_helloworld/models/forms/helloworld.js';
	}
	
	/**
	 * Method to get the data that should be injected in the form.
	 *
	 * @return  mixed  The data for the form.
	 *
	 * @since   1.6
	 */
	protected function loadFormData()
	{
		// Check the session for previously entered form data.
		$data = JFactory::getApplication()->getUserState(
			'com_helloworld.edit.helloworld.data',
			array()
		);

		if (empty($data))
		{
			$data = $this->getItem();
		}

		return $data;
	}
	/**
	 * Method to override the JModelAdmin save() function to handle Save as Copy correctly
	 *
	 * @param   The helloworld record data submitted from the form.
	 *
	 * @return  parent::save() return value
	 */
	public function save($data)
	{
		$input = JFactory::getApplication()->input;

		JLoader::register('CategoriesHelper', JPATH_ADMINISTRATOR . '/components/com_categories/helpers/categories.php');

		// Validate the category id
		// validateCategoryId() returns 0 if the catid can't be found
		if ((int) $data['catid'] > 0)
		{
			$data['catid'] = CategoriesHelper::validateCategoryId($data['catid'], 'com_helloworld');
		}

		// Alter the greeting and alias for save as copy
		if ($input->get('task') == 'save2copy')
		{
			$origTable = clone $this->getTable();
			$origTable->load($input->getInt('id'));

			if ($data['greeting'] == $origTable->greeting)
			{
				list($greeting, $alias) = $this->generateNewTitle($data['catid'], $data['alias'], $data['greeting']);
				$data['greeting'] = $greeting;
				$data['alias'] = $alias;
			}
			else
			{
				if ($data['alias'] == $origTable->alias)
				{
					$data['alias'] = '';
				}
			}
			// standard Joomla practice is to set the new record as unpublished
			$data['published'] = 0;
		}

		$result = parent::save($data);
		if ($result)
		{
			$this->getTable()->rebuild(1);
		}
		return $result;
	}
	/**
	 * Method to check if it's OK to delete a message. Overrides JModelAdmin::canDelete
	 */
	protected function canDelete($record)
	{
		if( !empty( $record->id ) )
		{
			return JFactory::getUser()->authorise( "core.delete", "com_helloworld.helloworld." . $record->id );
		}
	}
	/**
	 * Prepare a helloworld record for saving in the database
	 */
	protected function prepareTable($table)
	{
	}
	
	/**
	 * Save the record reordering after a record is dragged to a new position in the helloworlds view
	 */
	public function saveorder($idArray = null, $lft_array = null)
	{
		// Get an instance of the table object.
		$table = $this->getTable();

		if (!$table->saveorder($idArray, $lft_array))
		{
			$this->setError($table->getError());

			return false;
		}

		return true;
	}
}

Front End Form

Similar to the admin form, we add a tags field to the frontend form, except that we use the nested option and don't allow the user to define a new tag. We also include a published field with a default value of 1, but just set this to hidden.

site/models/forms/add-form.xml

<?xml version="1.0" encoding="utf-8"?>
<form
    addrulepath="/administrator/components/com_helloworld/models/rules"
    addfieldpath="/administrator/components/com_helloworld/models/fields"
    >
    <fieldset
				name="details"
				label="COM_HELLOWORLD_HELLOWORLD_DETAILS"
	>
		<field
				name="id"
				type="hidden"
				/>
		<field
				name="greeting"
				type="text"
				label="COM_HELLOWORLD_HELLOWORLD_GREETING_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_GREETING_DESC"
				size="40"
				class="inputbox"
				validate="greeting"
				required="true"
				hint="COM_HELLOWORLD_HELLOWORLD_GREETING_HINT"
				default=""
				/>
		<field 
				name="alias" 
				type="text" 
				label="JFIELD_ALIAS_LABEL"
				description="JFIELD_ALIAS_DESC"
				hint="JFIELD_ALIAS_PLACEHOLDER"
				size="40" 
				/>
		<field
				name="catid"
				type="category"
				extension="com_helloworld"
				class="inputbox"
				default=""
				label="COM_HELLOWORLD_HELLOWORLD_FIELD_CATID_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_FIELD_CATID_DESC"
				required="true"
				>
				<option value="0">JOPTION_SELECT_CATEGORY</option>
		</field>
		<fields name="imageinfo" label="COM_HELLOWORLD_HELLOWORLD_IMAGE_LABEL">
			<field
				name="image"
				type="file"
				label="COM_HELLOWORLD_HELLOWORLD_PICTURE_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_PICTURE_DESC" 
				accept="image/*"
				>
			</field>
			<field
 				name="caption"
				type="text"
				label="COM_HELLOWORLD_HELLOWORLD_CAPTION_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_CAPTION_DESC"
				size="40"
				class="inputbox"
				>
			</field>
			<field
				name="alt"
				type="text"
				label="COM_HELLOWORLD_HELLOWORLD_ALTTEXT_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_ALTTEXT_DESC"
				size="40"
				class="inputbox"
				>
			</field>
		</fields>
		<field
				name="language"
				type="contentlanguage"
				label="JFIELD_LANGUAGE_LABEL"
				description="JFIELD_LANGUAGE_DESC"
				class="inputbox">
		</field>
		<field 
				name="tags" 
				type="tag"
				label="JTAG" 
				description="JTAG_DESC"
				mode="nested"
				multiple="true">
		</field>
		<field
				name="message"
				type="textarea"
				rows="5"
				cols="80"
				label="COM_HELLOWORLD_HELLOWORLD_MESSAGE_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_MESSAGE_DESC"
				hint="COM_HELLOWORLD_HELLOWORLD_MESSAGE_HINT"
				required="true"
				>
        </field>
        <field
				name="captcha"
				type="captcha"
				label="COM_HELLOWORLD_HELLOWORLD_FIELD_CAPTCHA_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_FIELD_CAPTCHA_DESC"
				validate="captcha"
                >
		</field>
        <fields name="params">
            <field
                    name="show_category"
                    type="list"
                    label="COM_HELLOWORLD_HELLOWORLD_FIELD_SHOW_CATEGORY_LABEL"
                    description="COM_HELLOWORLD_HELLOWORLD_FIELD_SHOW_CATEGORY_DESC"
                    default=""
                    useglobal="true"
            >
                <option value="0">JHIDE</option>
                <option value="1">JSHOW</option>
            </field>
        </fields>
		<field
				name="parent_id"
				type="helloworldparent"
				label="COM_HELLOWORLD_HELLOWORLD_FIELD_PARENT_LABEL"
				description="COM_HELLOWORLD_HELLOWORLD_FIELD_PARENT_DESC"
				default="1"
				filter="int">
		</field>
		<field name="published" type="hidden" default="1" />
    </fieldset>
</form>

Frontend Hello World record display

In the view code we get the tag data using the TagsHelper::getItemTags() function. This time we need not only the tag ids, but also other information such as the tag alias and title, in order that the tag link can be constructed correctly in the html.

In the layout code we use the standard joomla layout in layouts/joomla/content/tags.php, and in the render() call we pass the tag data which was set up in the view. Note that this layout is designed to be used on the front end only.

site/views/helloworld/view.html.php

<?php
/**
 * @package     Joomla.Administrator
 * @subpackage  com_helloworld
 *
 * @copyright   Copyright (C) 2005 - 2018 Open Source Matters, Inc. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */

// No direct access to this file
defined('_JEXEC') or die('Restricted access');

/**
 * HTML View class for the HelloWorld Component
 *
 * @since  0.0.1
 */
class HelloWorldViewHelloWorld extends JViewLegacy
{
	/**
	 * Display the Hello World view
	 *
	 * @param   string  $tpl  The name of the template file to parse; automatically searches through the template paths.
	 *
	 * @return  void
	 */
	function display($tpl = null)
	{
		// Assign data to the view
		$this->item = $this->get('Item');

		// Check for errors.
		if (count($errors = $this->get('Errors')))
		{
			JLog::add(implode('<br />', $errors), JLog::WARNING, 'jerror');

			return false;
		}

		$this->addMap();

		$tagsHelper = new JHelperTags;
		$this->item->tags = $tagsHelper->getItemTags('com_helloworld.helloworld' , $this->item->id);

		$model = $this->getModel();
		$this->parentItem = $model->getItem($this->item->parent_id);
		$this->children = $model->getChildren($this->item->id);
		// getChildren includes the record itself (as well as the children) so remove this record
		unset($this->children[0]);

		// Display the view
		parent::display($tpl);
	}

	function addMap() 
	{
		$document = JFactory::getDocument();

		// everything's dependent upon JQuery
		JHtml::_('jquery.framework');

		// we need the Openlayers JS and CSS libraries
		$document->addScript("https://cdnjs.cloudflare.com/ajax/libs/openlayers/4.6.4/ol.js");
		$document->addStyleSheet("https://cdnjs.cloudflare.com/ajax/libs/openlayers/4.6.4/ol.css");

		// ... and our own JS and CSS
		$document->addScript(JURI::root() . "media/com_helloworld/js/openstreetmap.js");
		$document->addStyleSheet(JURI::root() . "media/com_helloworld/css/openstreetmap.css");

		// get the data to pass to our JS code
		$params = $this->get("mapParams");
		$document->addScriptOptions('params', $params);
	}
}

site/views/helloworld/tmpl/default.php

<?php
/**
 * @package     Joomla.Administrator
 * @subpackage  com_helloworld
 *
 * @copyright   Copyright (C) 2005 - 2018 Open Source Matters, Inc. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */

// No direct access to this file
defined('_JEXEC') or die('Restricted access');
$lang = JFactory::getLanguage()->getTag();
if (JLanguageMultilang::isEnabled() && $lang)
{
    $query_lang = "&lang={$lang}";
}
else
{
    $query_lang = "";
}
?>
<h1><?php echo $this->item->greeting.(($this->item->category and $this->item->params->get('show_category'))
                                      ? (' ('.$this->item->category.')') : ''); ?>
</h1>
<?php
    echo $this->item->description;
    $tagLayout = new JLayoutFile('joomla.content.tags');
    echo $tagLayout->render($this->item->tags);
    $src = $this->item->imageDetails['image'];
    if ($src)
    {
        $html = '<figure>
                    <img src="%s" alt="%s" >
                    <figcaption>%s</figcaption>
                </figure>';
        $alt = $this->item->imageDetails['alt'];
        $caption = $this->item->imageDetails['caption'];
        echo sprintf($html, $src, $alt, $caption);
    } ?>

<?php if ($this->parentItem->id > 1) : ?>
	<h1><?php echo JText::_('COM_HELLOWORLD_PARENT') ?>
	</h1>
	<h3>
		<?php $url = JRoute::_('index.php?option=com_helloworld&view=helloworld&id=' . $this->parentItem->id . ':' . $this->parentItem->alias . '&catid=' . $this->parentItem->catid . $query_lang); ?>
		<a href="<?php echo $url; ?>"><?php echo $this->parentItem->greeting; ?></a>
	</h3>
<?php endif; ?>

<?php if ($this->children) : 
		$baseLevel = $this->item->level; ?>
		<h1><?php echo JText::_('COM_HELLOWORLD_CHILDREN') ?>
		</h1>
		<?php foreach ($this->children as $i => $child) : ?>
			<h3>
				<?php $prefix = JLayoutHelper::render('joomla.html.treeprefix', array('level' => $child->level - $baseLevel)); ?>
				<?php echo $prefix; ?>
				<?php $url = JRoute::_('index.php?option=com_helloworld&view=helloworld&id=' . $child->id . ':' . $child->alias . '&catid=' . $child->catid . $query_lang); ?>
				<a href="<?php echo $url; ?>"><?php echo $child->greeting; ?></a>
			</h3>
	<?php endforeach; ?>
<?php endif; ?>

<div id="map" class="map"></div>
<div class="map-callout map-callout-bottom" id="greeting-container"></div>
<div id="searchmap">
    <?php echo '<input id="token" type="hidden" name="' . JSession::getFormToken() . '" value="1" />'; ?>
    <button type="button" class="btn btn-primary" onclick="searchHere();">
        <?php echo JText::_('COM_HELLOWORLD_SEARCH_HERE_BUTTON') ?>
    </button>
    <div id="searchresults">
    </div>
</div>

Site Route Helper

As mentioned in the Database section above, we add the methods getHelloworldRoute() and getCategoryRoute() to the site route helper file. This isn't strictly necessary because if we don't write these functions Joomla will use a default route helper, but it will be less performant than writing the code ourselves.

site/helpers/route.php

<?php

defined('_JEXEC') or die;

/**
 * Helloworld Component Helper file for generating the URL Routes
 *
 */
class HelloworldHelperRoute
{
	/**
	 * When the Helloworld message is displayed then there is also shown a map with a Search Here button.
	 * This function generates the URL which the Ajax call will use to perform the search. 
	 * 
	 */
	public static function getAjaxURL()
	{
		if (!JLanguageMultilang::isEnabled())
		{
			return null;
		}
        
		$lang = JFactory::getLanguage()->getTag();
		$app  = JFactory::getApplication();
		$sitemenu= $app->getMenu();
		$thismenuitem = $sitemenu->getActive();

		// if we haven't got an active menuitem, or we're currently on a menuitem 
		// with view=category or note = "Ajax", then just stay on it
		if (!$thismenuitem || strpos($thismenuitem->link, "view=category") !== false || $thismenuitem->note == "Ajax")
		{
			return null;
		}

		// look for a menuitem with the right language, and a note field of "Ajax"
		$menuitem = $sitemenu->getItems(array('language','note'), array($lang, "Ajax"));
		if ($menuitem)
		{
			$itemid = $menuitem[0]->id; 
			$url = JRoute::_("index.php?Itemid=$itemid&view=helloworld&format=json");
			return $url;
		}
		else
		{
			return null;
		}
	}

	/**
	 * Helper function for generating the URL to a Helloworld page
	 * This is needed for the Tags functionality
	 */
	public static function getHelloworldRoute($id, $catid = 0, $language = 0)
	{
		// Create the link
		$link = 'index.php?option=com_helloworld&view=helloworld&id=' . $id;

		if ((int) $catid > 1)
		{
			$link .= '&catid=' . $catid;
		}

		if ($language && $language !== '*' && JLanguageMultilang::isEnabled())
		{
			$link .= '&lang=' . $language;
		}

		return $link;
	}

	/**
	 * Helper function for generating the URL to a Helloworld Category page
	 * This is needed for the Tags functionality
	 */
	public static function getCategoryRoute($catid, $language = 0)
	{
		if ($catid instanceof JCategoryNode)
		{
			$id = $catid->id;
		}
		else
		{
			$id = (int) $catid;
		}

		if ($id < 1)
		{
			$link = '';
		}
		else
		{
			$link = 'index.php?option=com_helloworld&view=category&id=' . $id;

			if ($language && $language !== '*' && JLanguageMultilang::isEnabled())
			{
				$link .= '&lang=' . $language;
			}
		}

		return $link;
	}
}

Packaging the Component

Contents of your code directory. Each file link below takes you to the step in the tutorial which has the latest version of that source code file.

helloworld.xml

<?xml version="1.0" encoding="utf-8"?>
<extension type="component" version="3.0" method="upgrade">

	<name>COM_HELLOWORLD</name>
	<!-- The following elements are optional and free of formatting constraints -->
	<creationDate>January 2018</creationDate>
	<author>John Doe</author>
	<authorEmail>john.doe@example.org</authorEmail>
	<authorUrl>http://www.example.org</authorUrl>
	<copyright>Copyright Info</copyright>
	<license>License Info</license>
	<!--  The version string is recorded in the components table -->
	<version>0.0.28</version>
	<!-- The description is optional and defaults to the name -->
	<description>COM_HELLOWORLD_DESCRIPTION</description>

	<!-- Runs on install/uninstall/update; New in 2.5 -->
	<scriptfile>script.php</scriptfile>

	<install> <!-- Runs on install -->
		<sql>
			<file driver="mysql" charset="utf8">sql/install.mysql.utf8.sql</file>
		</sql>
	</install>
	<uninstall> <!-- Runs on uninstall -->
		<sql>
			<file driver="mysql" charset="utf8">sql/uninstall.mysql.utf8.sql</file>
		</sql>
	</uninstall>
	<update> <!-- Runs on update; New since J2.5 -->
		<schemas>
			<schemapath type="mysql">sql/updates/mysql</schemapath>
		</schemas>
	</update>

	<!-- Site Main File Copy Section -->
	<!-- Note the folder attribute: This attribute describes the folder
		to copy FROM in the package to install therefore files copied
		in this section are copied from /site/ in the package -->
	<files folder="site">
		<filename>index.html</filename>
		<filename>helloworld.php</filename>
		<filename>controller.php</filename>
		<filename>router.php</filename>
		<folder>controllers</folder>
		<folder>views</folder>
		<folder>models</folder>
		<folder>helpers</folder>
	</files>

		<languages folder="site/language">
			<language tag="en-GB">en-GB/en-GB.com_helloworld.ini</language>
			<language tag="fr-FR">fr-FR/fr-FR.com_helloworld.ini</language>
		</languages>

	<media destination="com_helloworld" folder="media">
		<filename>index.html</filename>
		<folder>images</folder>
		<folder>js</folder>
		<folder>css</folder>
	</media>

	<administration>
		<!-- Administration Menu Section -->
		<menu link='index.php?option=com_helloworld' img="../media/com_helloworld/images/tux-16x16.png">COM_HELLOWORLD_MENU</menu>
		<!-- Administration Main File Copy Section -->
		<!-- Note the folder attribute: This attribute describes the folder
			to copy FROM in the package to install therefore files copied
			in this section are copied from /admin/ in the package -->
		<files folder="admin">
			<!-- Admin Main File Copy Section -->
			<filename>index.html</filename>
			<filename>config.xml</filename>
			<filename>helloworld.php</filename>
			<filename>controller.php</filename>
			<filename>access.xml</filename>
			<!-- SQL files section -->
			<folder>sql</folder>
			<!-- tables files section -->
			<folder>tables</folder>
			<!-- models files section -->
			<folder>models</folder>
			<!-- views files section -->
			<folder>views</folder>
			<!-- controllers files section -->
			<folder>controllers</folder>
			<!-- helpers files section -->
			<folder>helpers</folder>
		</files>
		<languages folder="admin/language">
			<language tag="en-GB">en-GB/en-GB.com_helloworld.ini</language>
			<language tag="en-GB">en-GB/en-GB.com_helloworld.sys.ini</language>
			<language tag="fr-FR">fr-FR/fr-FR.com_helloworld.ini</language>
			<language tag="fr-FR">fr-FR/fr-FR.com_helloworld.sys.ini</language>
		</languages>
	</administration>

</extension>

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