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Baum

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Nested Set implementation for Laravel

Baum is an implementation of the Nested Set pattern for the Laravel Eloquent ORM.

Key Considerations for using a Nested Set Pattern:

1. The Nested Set pattern is appropriate when the tree element and one or two attributes are the only data.
2. The Nested Set pattern is a poor choice when more complex relational data exists for the elements in the tree.
3. The Nested Set pattern is best when you need to query a tree more frequently than you need to modify the tree.

If you find a bug, please file an issue and submit a pull request with a failing unit test.

Documentation

• About Nested Sets
• The theory behind, a TL;DR version
• Installation
• Getting started
• Usage
• Further information
• Contributing

About Nested Sets

A nested set is a smart way to implement an ordered tree that allows for fast, non-recursive queries. For example, you can fetch all descendants of a node in a single query, no matter how deep the tree. The drawback is that insertions/moves/deletes require complex SQL, but that is handled behind the curtains by this package!

Nested sets are appropriate for ordered trees (e.g. menus, commercial categories) and big trees that must be queried efficiently (e.g. threaded posts).

See the wikipedia entry for nested sets for more info.

The theory behind, a TL;DR version

An easy way to visualize how a nested set works is to think of a parent entity surrounding all of its children, and its parent surrounding it, etc. So this tree:

root
  |_ Child 1
    |_ Child 1.1
    |_ Child 1.2
  |_ Child 2
    |_ Child 2.1
    |_ Child 2.2

Could be visualized like this:

 ___________________________________________________________________
|  Root                                                             |
|    ____________________________    ____________________________   |
|   |  Child 1                  |   |  Child 2                  |   |
|   |   __________   _________  |   |   __________   _________  |   |
|   |  |  C 1.1  |  |  C 1.2 |  |   |  |  C 2.1  |  |  C 2.2 |  |   |
1   2  3_________4  5________6  7   8  9_________10 11_______12 13  14
|   |___________________________|   |___________________________|   |
|___________________________________________________________________|

The numbers represent the left and right boundaries. The table then might look like this:

id | parent_id | lft  | rgt  | depth | data
 1 |           |    1 |   14 |     0 | root
 2 |         1 |    2 |    7 |     1 | Child 1
 3 |         2 |    3 |    4 |     2 | Child 1.1
 4 |         2 |    5 |    6 |     2 | Child 1.2
 5 |         1 |    8 |   13 |     1 | Child 2
 6 |         5 |    9 |   10 |     2 | Child 2.1
 7 |         5 |   11 |   12 |     2 | Child 2.2

To get all children of a parent node, you

To get the number of children, it's

To get a node and all its ancestors going back to the root, you

As you can see, queries that would be recursive and prohibitively slow on ordinary trees are suddenly quite fast. Nifty, isn't it?

Installation

You can add it to your project with:

Getting started

After the package is correctly installed the easiest way to get started is to run the provided generator:

Replace model by the class name you plan to use for your Nested Set model.

The generator will create a model file in your application configured to work with the Nested Set behaviour provided by Baum. You SHOULD take a look at those files, as each of them describes how they can be customized.

Next, you would probably run artisan migrate to apply the migration.

Model configuration

In order to work with Baum, you must ensure that your model class extends Baum\Node.

This is the easiest it can get:

This is a slightly more complex example where we have the column names customized:

Remember that, obviously, the column names must match those in the database table.

Migration configuration

You must ensure that the database table that supports your Baum models has the following columns:

• parent_id: a reference to the parent (int)
• lft: left index bound (int)
• rgt: right index bound (int)
• depth: depth or nesting level (int)

Here is a sample migration file:

You may freely modify the column names, provided you change them both in the migration and the model.

Usage

After you've configured your model and run the migration, you are now ready to use Baum with your model. Below are some examples.

• Baum
  • Nested Set implementation for Laravel
  • Key Considerations for using a Nested Set Pattern:
  • Documentation
  • About Nested Sets
  • The theory behind, a TL;DR version
  • Installation
  • Getting started
  • Model configuration
  • Migration configuration
  • Usage
  • Creating a root node
  • Inserting nodes
  • Deleting nodes
  • Getting the nesting level of a node
  • Moving nodes around
  • Asking questions to your nodes
  • Relations
  • Root and Leaf scopes
  • Accessing the ancestry/descendancy chain
  • Limiting the levels of children returned
  • Custom sorting column
  • Dumping the hierarchy tree
  • Model events: moving and moved
  • Scope support
  • Validation
  • Tree rebuilding
  • Soft deletes
  • Seeding/Mass-assignment
  • Misc/Utility functions
    • Node extraction query scopes
    • Get a nested list of column values
  • Contributing
  • License

Creating a root node

By default, all nodes are created as roots:

Alternatively, you may find yourself in the need of converting an existing node into a root node:

You may also nullify it's parent_id column to accomplish the same behaviour:

Inserting nodes

Deleting nodes

Descendants of deleted nodes will also be deleted and all the lft and rgt bound will be recalculated. Pleases note that, for now, deleting and deleted model events for the descendants will not be fired.

Getting the nesting level of a node

The getLevel() method will return current nesting level, or depth, of a node.

Moving nodes around

Baum provides several methods for moving nodes around:

• moveLeft(): Find the left sibling and move to the left of it.
• moveRight(): Find the right sibling and move to the right of it.
• moveToLeftOf($otherNode): Move to the node to the left of ...
• moveToRightOf($otherNode): Move to the node to the right of ...
• makeNextSiblingOf($otherNode): Alias for moveToRightOf.
• makeSiblingOf($otherNode): Alias for makeNextSiblingOf.
• makePreviousSiblingOf($otherNode): Alias for moveToLeftOf.
• makeChildOf($otherNode): Make the node a child of ...
• makeFirstChildOf($otherNode): Make the node the first child of ...
• makeLastChildOf($otherNode): Alias for makeChildOf.
• makeRoot(): Make current node a root node.

For example:

Asking questions to your nodes

You can ask some questions to your Baum nodes:

• isRoot(): Returns true if this is a root node.
• isLeaf(): Returns true if this is a leaf node (end of a branch).
• isChild(): Returns true if this is a child node.
• isChildOf($other): Returns true if this node is a child of the other.
• isDescendantOf($other): Returns true if node is a descendant of the other.
• isSelfOrDescendantOf($other): Returns true if node is self or a descendant.
• isAncestorOf($other): Returns true if node is an ancestor of the other.
• isSelfOrAncestorOf($other): Returns true if node is self or an ancestor.
• equals($node): current node instance equals the other.
• insideSubtree($node): Checks whether the given node is inside the subtree defined by the left and right indices.
• inSameScope($node): Returns true if the given node is in the same scope as the current one. That is, if every column in the scoped property has the same value in both nodes.

Using the nodes from the previous example:

Relations

Baum provides two self-referential Eloquent relations for your nodes: parent and children.

Root and Leaf scopes

Baum provides some very basic query scopes for accessing the root and leaf nodes:

You may also be interested in only the first root:

Accessing the ancestry/descendancy chain

There are several methods which Baum offers to access the ancestry/descendancy chain of a node in the Nested Set tree. The main thing to keep in mind is that they are provided in two ways:

First as query scopes, returning an Illuminate\Database\Eloquent\Builder instance to continue to query further. To get actual results from these, remember to call get() or first().

• ancestorsAndSelf(): Targets all the ancestor chain nodes including the current one.
• ancestors(): Query the ancestor chain nodes excluding the current one.
• siblingsAndSelf(): Instance scope which targets all children of the parent, including self.
• siblings(): Instance scope targeting all children of the parent, except self.
• leaves(): Instance scope targeting all of its nested children which do not have children.
• descendantsAndSelf(): Scope targeting itself and all of its nested children.
• descendants(): Set of all children & nested children.
• immediateDescendants(): Set of all children nodes (non-recursive).

Second, as methods which return actual Baum\Node instances (inside a Collection object where appropiate):

• getRoot(): Returns the root node starting at the current node.
• getAncestorsAndSelf(): Retrieve all of the ancestor chain including the current node.
• getAncestorsAndSelfWithoutRoot(): All ancestors (including the current node) except the root node.
• getAncestors(): Get all of the ancestor chain from the database excluding the current node.
• getAncestorsWithoutRoot(): All ancestors except the current node and the root node.
• getSiblingsAndSelf(): Get all siblings of the node, including the node itself.
• getSiblings(): Get all siblings of the node, excluding the current node.
• getLeaves(): Return all of its nested children which do not have children.
• getDescendantsAndSelf(): Retrieve all nested children and self.
• getDescendants(): Retrieve all of its children & nested children.
• getImmediateDescendants(): Retrieve all of its children nodes (non-recursive).

Here's a simple example for iterating a node's descendants (provided a name attribute is available):

Limiting the levels of children returned

In some situations where the hierarchy depth is huge it might be desirable to limit the number of levels of children returned (depth). You can do this in Baum by using the limitDepth query scope.

The following snippet will get the current node's descendants up to a maximum of 5 depth levels below it:

Similarly, you can limit the descendancy levels with both the getDescendants and getDescendantsAndSelf methods by supplying the desired depth limit as the first argument:

Custom sorting column

By default in Baum all results are returned sorted by the lft index column value for consistency.

If you wish to change this default behaviour you need to specify in your model the name of the column you wish to use to sort your results like this:

Dumping the hierarchy tree

Baum extends the default Eloquent\Collection class and provides the toHierarchy method to it which returns a nested collection representing the queried tree.

Retrieving a complete tree hierarchy into a regular Collection object with its children properly nested is as simple as:

Model events: moving and moved

Baum models fire the following events: moving and moved every time a node is moved around the Nested Set tree. This allows you to hook into those points in the node movement process. As with normal Eloquent model events, if false is returned from the moving event, the movement operation will be cancelled.

The recommended way to hook into those events is by using the model's boot method:

Scope support

Baum provides a simple method to provide Nested Set "scoping" which restricts what we consider part of a nested set tree. This should allow for multiple nested set trees in the same database table.

To make use of the scoping funcionality you may override the scoped model attribute in your subclass. This attribute should contain an array of the column names (database fields) which shall be used to restrict Nested Set queries:

In the previous example, company_id effectively restricts (or "scopes") a Nested Set tree. So, for each value of that field we may be able to construct a full different tree.

All methods which ask or traverse the Nested Set tree will use the scoped attribute (if provided).

Please note that, for now, moving nodes between scopes is not supported.

Validation

The ::isValidNestedSet() static method allows you to check if your underlying tree structure is correct. It mainly checks for these 3 things:

• Check that the bound indexes lft, rgt are not null, rgt values greater than lft and within the bounds of the parent node (if set).
• That there are no duplicates for the lft and rgt column values.
• As the first check does not actually check root nodes, see if each root has the lft and rgt indexes within the bounds of its children.

All of the checks are scope aware and will check each scope separately if needed.

Example usage, given a Category node class:

Tree rebuilding

Baum supports for complete tree-structure rebuilding (or reindexing) via the ::rebuild() static method.

This method will re-index all your lft, rgt and depth column values, inspecting your tree only from the parent <-> children relation standpoint. Which means that you only need a correctly filled parent_id column and Baum will try its best to recompute the rest.

This can prove quite useful when something has gone horribly wrong with the index values or it may come quite handy when converting from another implementation (which would probably have a parent_id column).

This operation is also scope aware and will rebuild all of the scopes separately if they are defined.

Simple example usage, given a Category node class:

No checks are made to see if the tree is already valid, meaning a call to rebuild will always rebuild the tree, whether it is valid or not. If you don't want this behaviour, don't call rebuild if isValidNestedSet returns true.

Soft deletes

Using soft deletes / restore() is not recommeded and may cause problems if a tree has been modified after a soft delete operation.

Seeding/Mass-assignment

Because Nested Set structures usually involve a number of method calls to build a hierarchy structure (which result in several database queries), Baum provides two convenient methods which will map the supplied array of node attributes and create a hierarchy tree from them:

• buildTree($nodeList): (static method) Maps the supplied array of node attributes into the database.
• makeTree($nodeList): (instance method) Maps the supplied array of node attributes into the database using the current node instance as the parent for the provided subtree.

Both methods will create new nodes when the primary key is not supplied, update or create if it is, and delete all nodes which are not present in the affecting scope. Understand that the affecting scope for the buildTree static method is the whole nested set tree and for the makeTree instance method are all of the current node's descendants.

For example, imagine we wanted to map the following category hierarchy into our database:

• TV & Home Theater
• Tablets & E-Readers
• Computers
  • Laptops
  • PC Laptops
  • Macbooks (Air/Pro)
  • Desktops
  • Monitors
• Cell Phones

This could be easily accomplished with the following code:

After that, we may just update the hierarchy as needed:

The makeTree instance method works in a similar fashion. The only difference is that it will only perform operations on the descendants of the calling node instance.

So now imagine we already have the following hierarchy in the database:

• Electronics
• Health Fitness & Beaty
• Small Appliances
• Major Appliances

If we execute the following code:

Would result in:

• Electronics
  • TV & Home Theater
  • Tablets & E-Readers
  • Computers
  • Laptops
    • PC Laptops
    • Macbooks (Air/Pro)
  • Desktops
  • Monitors
  • Cell Phones
• Health Fitness & Beaty
• Small Appliances
• Major Appliances

Updating and deleting nodes from the subtree works the same way.

Misc/Utility functions

Node extraction query scopes

Baum provides some query scopes which may be used to extract (remove) selected nodes from the current results set.

• withoutNode(node): Extracts the specified node from the current results set.
• withoutSelf(): Extracts itself from the current results set.
• withoutRoot(): Extracts the current root node from the results set.

Get a nested list of column values

The ::getNestedList() static method returns a key-value pair array indicating a node's depth. Useful for silling select elements, etc.

It expects the column name to return, and optionally: the column to use for array keys (will use id if none supplied) and/or a separator:

An example use case:

Contributing

Thinking of contributing? Maybe you've found some nasty bug or want to add a new feature? That's great news!

Please see the CONTRIBUTING.md file for extended guidelines and/or recommendations.

License

Baum is licensed under the terms of the MIT License (See LICENSE file for details).