Difference between #10 and #5 of Display an AJAX tree from your DB using CTreeView

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Title
Display an AJAX tree from your DB using CTreeView
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Category
Tutorials
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Tags
AJAXAJAX, CTreeView
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Content
This example uses a MySQL DB with a table named `tree` with the fields `id`,
`name`, and `parent_id`. The `parent_id` will be `NULL` for root elements.
The SQL is kept simple (no autoinc, no FK, etc).

~~~~
[sql]
CREATE TABLE tree (
  id INTEGER UNSIGNED,UNSIGNED NOT NULL,
  name VARCHAR(50) NOT NULL,
  parent_id INTEGER UNSIGNED,
  PRIMARY(id)PRIMARY KEY (id)
)
~~~~

MySQL has no recursive queries. In order to fetch tree nodes, you have to
recursively send SQL queries for each node, asking for its children. The easiest
way to do so is to send these queries with AJAX, so that the tree can be
displayed even if the deep nodes haven't been fetched yet. If you're using
Oracle or Postgresql, there are other solutions, though this will also
work.

In your view, add:

~~~~
[php]
<?php
$this->widget(
	'CTreeView',
	array('url' => array('ajaxFillTree'))
);
?>
~~~~

This will create a tree widget
[CTreeView](http://www.yiiframework.com/doc/api/1.1/CTreeView/) on your
page, and its data will be fetch using the `ajaxFillTree` of the current
controller.

So we have to add this action to the controller:

~~~~
[php] 
	/**
	 * Fills the JS tree on an AJAX request.
	 * Should receive parent node ID in $_GET['root'],
	 *  with 'source' when there is no parent.
	 */
	public function actionAjaxFillTree()
	{
		if (!Yii::app()->request->isAjaxRequest) {
			exit();
		}
		$parentId = 0;"NULL";
		if (isset($_GET['root']))(isset($_GET['root']) &&
$_GET['root'] !== 'source') {
			$parentId = (int) $_GET['root'];
		}
		$req = Yii::app()->db->createCommand(
			"SELECT m1.id, m1.name AS text, m2.id IS NOT NULL AS hasChildren "
			. "FROM tree AS m1 LEFT JOIN tree AS m2 ON m1.id=m2.parent_id "
			. "WHERE m1.parent_id <=> $parentId "
			. "GROUP BY m1.id ORDER BY m1.name ASC"
		);
		$children = $req->queryAll();
		echo str_replace(
			'"hasChildren":"0"',
			'"hasChildren":false',
			CTreeView::saveDataAsJson($children)
		);
		exit();
	}
~~~~

When the page loads, an AJAX request will be sent to fill the first level of the
tree. It'll have the GET parameter `root` set to
`source`.`source` (this is the behavior of the
[Treeview](http://bassistance.de/jquery-plugins/jquery-plugin-treeview/) JS
plugin that [CTreeView](http://www.yiiframework.com/doc/api/1.1/CTreeView/)
uses). We suppose here that the corresponding nodes (the root
nodes) have a `parent_id` of 0. You can replace this by `NULL` if
necessary, andset to `NULL`. In SQL, "=" can't compare a
value with `NULL`, so we have to use the SQL request will still work
because it uses `<=>` instead of `=`).operator
instead.

The other AJAX requests will have an integer value (the parent node's id) in
`$_GET['root']`. We typecast this to "int" for security.

Then we readthe code reads the data in the database. We
need a LEFT JOIN*LEFT JOIN* to find if a node has
children. If each row already has a `hasChildren` field, you can remove this
join and your SQL will be faster.

When sending the JSON-encoded result, there's a little trick: the javascript
wants the `hasChildren` attribute to be a boolean. But the SQL result just
contains 0 or 1, so we have to convert it, at least for the "false"
case. Instead of operating on the string result, one could modify the PHP array
with a `foreach`.

The `exit()` might not be necessary, but if you enabled the logs to
Firebug,Firebug or extensions like a debug toolbar, then
Yii will write some JS at the end of your response, and it will break your
AJAX.the JSON format.

### Links
[Chinese version](http://projects.ourplanet.tk/node/100)