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In the previous section, we used existing data and checked that it looked hierarchal via the method generatetreelist. However, usually you would add your data in exactly the same way as you would for any model. For example:

// pseudo controller code
$data['Category']['parent_id'] =  3;
$data['Category']['name'] =  'Skating';
$this->Category->save($data);

1. // pseudo controller code
2. $data['Category']['parent_id'] = 3;
3. $data['Category']['name'] = 'Skating';
4. $this->Category->save($data);

When using the tree behavior its not necessary to to do any more than set the parent_id, and the tree behavior will take care of the rest. If you don't set the parent_id, the tree behavior will add to the tree making your new addition a new top level entry:

// pseudo controller code
$data = array();
$data['Category']['name'] =  'Other People\'s Categories';
$this->Category->save($data);

1. // pseudo controller code
2. $data = array();
3. $data['Category']['name'] = 'Other People\'s Categories';
4. $this->Category->save($data);

Running the above two code snippets would alter your tree as follows:

• My Categories
  • Fun
    • Sport
      • Surfing
      • Extreme knitting
      • Skating New
    • Friends
      • Gerald
      • Gwendolyn
  • Work
    • Reports
      • Annual
      • Status
    • Trips
      • National
      • International
• Other People's Categories New

Modifying data is as transparent as adding new data. If you modify something, but do not change the parent_id field - the structure of your data will remain unchanged. For example:

// pseudo controller code
$this->Category->id = 5; // id of Extreme knitting
$this->Category->save(array('name' =>'Extreme fishing'));

1. // pseudo controller code
2. $this->Category->id = 5; // id of Extreme knitting
3. $this->Category->save(array('name' =>'Extreme fishing'));

The above code did not affect the parent_id field - even if the parent_id is included in the data that is passed to save if the value doesn't change, neither does the data structure. Therefore the tree of data would now look like:

• My Categories
  • Fun
    • Sport
      • Surfing
      • Extreme fishing Updated
      • Skating
    • Friends
      • Gerald
      • Gwendolyn
  • Work
    • Reports
      • Annual
      • Status
    • Trips
      • National
      • International
• Other People's Categories

Moving data around in your tree is also a simple affair. Let's say that Extreme fishing does not belong under Sport, but instead should be located under Other People's Categories. With the following code:

// pseudo controller code
$this->Category->id = 5; // id of Extreme fishing
$newParentId = $this->Category->field('id', array('name' => 'Other People\'s Categories'));
$this->Category->save(array('parent_id' => $newParentId)); 

1. // pseudo controller code
2. $this->Category->id = 5; // id of Extreme fishing
3. $newParentId = $this->Category->field('id', array('name' => 'Other People\'s Categories'));
4. $this->Category->save(array('parent_id' => $newParentId));

As would be expected the structure would be modified to:

• My Categories
  • Fun
    • Sport
      • Surfing
      • Skating
    • Friends
      • Gerald
      • Gwendolyn
  • Work
    • Reports
      • Annual
      • Status
    • Trips
      • National
      • International
• Other People's Categories
  • Extreme fishing Moved

The tree behavior provides a number of ways to manage deleting data. To start with the simplest example; let's say that the reports category is no longer useful. To remove it and any children it may have just call delete as you would for any model. For example with the following code:

// pseudo controller code
$this->Category->id = 10;
$this->Category->delete();

1. // pseudo controller code
2. $this->Category->id = 10;
3. $this->Category->delete();

The category tree would be modified as follows:

• My Categories
  • Fun
    • Sport
      • Surfing
      • Skating
    • Friends
      • Gerald
      • Gwendolyn
  • Work
    • Trips
      • National
      • International
• Other People's Categories
  • Extreme fishing

Using and manipulating hierarchical data can be a tricky business. In addition to the core find methods, with the tree behavior there are a few more tree-orientated permutations at your disposal.

Most tree behavior methods return and rely on data being sorted by the lft field. If you call find() and do not order by lft, or call a tree behavior method and pass a sort order, you may get undesirable results.

The children method takes the primary key value (the id) of a row and returns the children, by default in the order they appear in the tree. The second optional parameter defines whether or not only direct children should be returned. Using the example data from the previous section:

$allChildren = $this->Category->children(1); // a flat array with 11 items
// -- or --
$this->Category->id = 1;
$allChildren = $this->Category->children(); // a flat array with 11 items

// Only return direct children
$directChildren = $this->Category->children(1, true); // a flat array with 2 items

1. $allChildren = $this->Category->children(1); // a flat array with 11 items
2. // -- or --
3. $this->Category->id = 1;
4. $allChildren = $this->Category->children(); // a flat array with 11 items
5. // Only return direct children
6. $directChildren = $this->Category->children(1, true); // a flat array with 2 items

If you want a recursive array use find('threaded')

As with the method children, childCount takes the primary key value (the id) of a row and returns how many children it has. The second optional parameter defines whether or not only direct children are counted. Using the example data from the previous section:

$totalChildren = $this->Category->childCount(1); // will output 11
// -- or --
$this->Category->id = 1;
$directChildren = $this->Category->childCount(); // will output 11

// Only counts the direct descendants of this category
$numChildren = $this->Category->childCount(1, true); // will output 2

1. $totalChildren = $this->Category->childCount(1); // will output 11
2. // -- or --
3. $this->Category->id = 1;
4. $directChildren = $this->Category->childCount(); // will output 11
5. // Only counts the direct descendants of this category
6. $numChildren = $this->Category->childCount(1, true); // will output 2

This method will return data similar to find('list'), with an indented prefix to show the structure of your data. Below is an example of what you can expect this method to return see the api for the other find-like parameters.

array(
	[1] =>  "My Categories",
	[2] =>  "_Fun",
	[3] =>  "__Sport",
	[4] =>  "___Surfing",
	[16] => "___Skating",
	[6] =>  "__Friends",
	[7] =>  "___Gerald",
	[8] =>  "___Gwendolyn",
	[9] =>  "_Work",
	[13] => "__Trips",
	[14] => "___National",
	[15] => "___International",
	[17] => "Other People's Categories",
	[5] =>  "_Extreme fishing"
)

This convenience function will, as the name suggests, return the parent node for any node, or false if the node has no parent (its the root node). For example:

$parent = $this->Category->getparentnode(2); //<- id for fun
// $parent contains All categories

1. $parent = $this->Category->getparentnode(2); //<- id for fun
2. // $parent contains All categories

The 'path' when refering to hierachial data is how you get from where you are to the top. So for example the path from the category "International" is:

• My Categories
  • ...
  • Work
    • Trips
      • ...
      • International

Using the id of "International" getpath will return each of the parents in turn (starting from the top).

$parents = $this->Category->getpath(15);

1. $parents = $this->Category->getpath(15);

// contents of $parents
array(
	[0] =>  array('Category' => array('id' => 1, 'name' => 'My Categories', ..)),
	[1] =>  array('Category' => array('id' => 9, 'name' => 'Work', ..)),
	[2] =>  array('Category' => array('id' => 13, 'name' => 'Trips', ..)),
	[3] =>  array('Category' => array('id' => 15, 'name' => 'International', ..)),
)