baril/bonsai

An implementation of the Closure Tables pattern for Eloquent.

v2.0.0 2021-07-17 08:06 UTC

This package is auto-updated.

Last update: 2021-07-17 08:09:36 UTC


README

This package is an implementation of the "Closure Table" design pattern for Laravel 6 and MySQL. This pattern allows for faster querying of tree-like structures stored in a relational database. It is an alternative to nested sets.

Version compatibility

Laravel Bonsai
5.6+ use Smoothie instead
6.x 1.x
7.x 1.x
8.x 2.x

Closure Table pattern

Let's say you have a tags table that contains a hierarchical list of tags. You probably have a self-referencing foreign key called parent_id or something similar.

The Closure Table pattern says you will create a secondary table (let's call it tag_tree) with the following columns:

  • ancestor_id: foreign key to your main table,
  • descendant_id: foreign key to your main table,
  • depth: unsigned integer.

The table contains all possible combinations of an ancestor and a descendant. For example, the following tree:

1
├ 2
│ ├ 3
│ └ 4
└ 5

will produce the following closures:

ancestor_id descendant_id depth
1 1 0
1 2 1
1 3 2
1 4 2
1 5 1
2 2 0
2 3 1
2 4 1
3 3 0
4 4 0
5 5 0

Setup

New install

First, your main table needs a parent_id column (the name can be configured). This column is the one that holds the canonical data: the closures are merely a duplication of that information.

Then, have your model implement the Baril\Bonsai\Concerns\BelongsToTree trait.

You can use the following properties to configure the table and column names:

  • $parentForeignKey: name of the self-referencing foreign key in the main table (defaults to parent_id),
  • $closureTable: name of the closure table (defaults to the snake-cased model name suffixed with _tree, eg. tag_tree).
class Tag extends \Illuminate\Database\Eloquent\Model
{
    use \Baril\Bonsai\Concerns\BelongsToTree;

    protected $parentForeignKey = 'parent_tag';
    protected $closureTable = 'tag_closures';
}

The bonsai:grow command will generate the migration file for the closure table based on your model configuration:

php artisan bonsai:grow "App\\Models\\Tag"

If you use the --migrate option, the command will also run the migration. If your main table already contains data, it will also insert the closures for the existing data.

php artisan bonsai:grow "App\\Models\\Tag" --migrate

⚠️ If you use the --migrate option, any other pending migrations will run too.

There are some additional options: use --help to learn more.

Artisan commands

In addition to the bonsai:grow command described above, this package provides the following commands:

In case your data gets corrupt somehow, the bonsai:fix command will truncate the closure table and fill it again (based on the data found in the main table's parent_id column):

php artisan bonsai:fix "App\\Models\\Tag"

The bonsai:show command provides a quick-and-easy way to output the content of the tree. It takes a label parameter that defines which column (or accessor) to use as label. Optionally you can also specify a max depth.

php artisan bonsai:show "App\\Models\\Tag" --label=name --depth=3

Basic usage

Just fill the model's parent_id and save the model: the closure table will be updated accordingly.

$tag = Tag::find($tagId);
$tag->parent_id = $parentTagId; // or: $tag->parent()->associate($parentTag);
$tag->save();

The save method will throw a \Baril\Bonsai\TreeException in case of a redundancy error (ie. if the parent_id corresponds to the model itself or one of its descendants).

When you delete a model, its closures will be automatically deleted. If the model has descendants, the delete method will throw a TreeException. You need to use one of these 2 methods instead:

  • deleteTree will delete the node and all its descendants,
  • deleteNode will remove the node from the tree, ie. attach its children to its parent (or make them roots if the node being deleted is a root), and then delete the node.
try {
    $tag->delete();
} catch (\Baril\Bonsai\TreeException $e) {
    // some specific treatment
    // ...
    $tag->deleteTree();
}

Relationships

The trait defines the following relationships:

  • parent: BelongsTo relation to the parent,
  • children: HasMany relation to the children,
  • ancestors: BelongsToMany relation to the ancestors,
  • descendants: BelongsToMany relation to the descendants,
  • siblings: HasMany relation to the other children of the same parent (requires to install the package baril/octopus).

⚠️ The ancestors and descendants relations are read-only! Trying to use the attach or detach method on them will throw an exception.

The ancestors and descendants relations have the following methods:

  • includingSelf(): will include the item itself in the results of the relation,
  • orderByDepth($direction = 'asc'),
  • upToDepth($depth): will retrieve ancestors/descendants up to (and including) the provided $depth.

Loading or eager-loading the descendants relation will automatically load the children relation (with no additional query). Furthermore, it will load the children relation recursively for all the eager-loaded descendants:

$tags = Tag::with('descendants')->limit(10)->get();

// The following code won't execute any new query:
foreach ($tags as $tag) {
    dump($tag->name);
    foreach ($tag->children as $child) {
        dump('-' . $child->name);
        foreach ($child->children as $grandchild) {
            dump('--' . $grandchild->name);
        }
    }
}

Of course, same goes with the ancestors and parent relations.

Methods

The trait defines the following methods:

  • isRoot(): returns true if the item's parent_id is null,
  • isLeaf(): checks if the item is a leaf (ie. has no children),
  • hasChildren(): $tag->hasChildren() is similar to !$tag->isLeaf(), albeit more readable,
  • isChildOf($item),
  • isParentOf($item),
  • isDescendantOf($item),
  • isAncestorOf($item),
  • isSiblingOf($item),
  • findCommonAncestorWith($item): returns the first common ancestor between 2 items, or null if they don't have a common ancestor (which can happen if the tree has multiple roots),
  • getDistanceTo($item): returns the "distance" between 2 items,
  • getDepth(): returns the depth of the item in the tree (the root element's depth is 0),
  • getSubtreeDepth(): returns the depth of the subtree of which the item is the root (0 if the item is a leaf).

Also, the getTree static method can be used to retrieve the whole tree:

$tags = Tag::getTree();

It will return a collection of the root elements, with the children relation eager-loaded on every element up to the leafs.

Query scopes

  • withAncestors($depth = null, $constraints = null): shortcut to with('ancestors'), with the added ability to specify a $depth limit (eg. $query->withAncestors(1) will only load the direct parent). Optionally, you can pass additional $constraints.
  • withDescendants($depth = null, $constraints = null).
  • withDepth($as = 'depth'): will add a depth column (or whatever alias you provided) on your resulting models.
  • whereIsRoot($bool = true): limits the query to the items with no parent (the behavior of the scope can be reversed by setting the $bool argument to false).
  • whereIsLeaf($bool = true).
  • whereHasChildren($bool = true): is just the opposite of whereIsLeaf.
  • whereIsDescendantOf($ancestor, $maxDepth = null, $includingSelf = false): limits the query to the descendants of $ancestor, with an optional $maxDepth. If the $includingSelf parameter is set to true, the ancestor will be included in the query results too. (The $ancestor parameter can be either the id or the Model itself.)
  • whereIsAncestorOf($descendant, $maxDepth = null, $includingSelf = false).

Ordered tree

In case you need each level of the tree to be explicitely ordered, you can use the Baril\Bonsai\Concerns\BelongsToOrderedTree trait (instead of BelongsToTree). In order to use this, you need the Orderly package in addition to Bonsai:

composer require baril/orderly

You will need a position column in your main table (the name of the column can be configured with the $orderColumn property).

class Tag extends \Illuminate\Database\Eloquent\Model
{
    use \Baril\Bonsai\Concerns\BelongsToOrderedTree;

    protected $orderColumn = 'order';
}

The children relation will now be ordered. In case you need to order it by some other field, you need to use the unordered scope first:

$children = $this->children()->unordered()->orderBy('name');

Also, all methods defined by the Orderable trait described in the Orderly package documentation will now be available:

$lastChild->moveToPosition(1);