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Nested Set

Nested Set behavior for Yii 2: https://github.com/creocoder/yii2-nested-sets

This extension allows managing trees stored in database as nested sets. It's implemented as Active Record behavior.

Installing and configuring

First you need to configure model as follows:

There is no need to validate fields specified in leftAttribute, rightAttribute, rootAttribute and levelAttribute options. Moreover, there could be problems if there are validation rules for these. Please check if there are no rules for fields mentioned in model's rules() method.

In case of storing a single tree per database, DB structure can be built with extensions/yiiext/behaviors/trees/schema.sql. If you're going to store multiple trees you'll need extensions/yiiext/behaviors/trees/schema_many_roots.sql.

By default leftAttribute, rightAttribute and levelAttribute values are matching field names in default DB schemas so you can skip configuring these.

There are two ways this behavior can work: one tree per table and multiple trees per table. The mode is selected based on the value of hasManyRoots option that is false by default meaning single tree mode. In multiple trees mode you can set rootAttribute option to match existing field in the table storing the tree.

Selecting from a tree

In the following we'll use an example model Category with the following in its DB:

- 1. Mobile phones
    - 2. iPhone
    - 3. Samsung
        - 4. X100
        - 5. C200
    - 6. Motorola
- 7. Cars
    - 8. Audi
    - 9. Ford
    - 10. Mercedes

In this example we have two trees. Tree roots are ones with ID=1 and ID=7.

Getting all roots

Using NestedSetBehavior::roots():

Result:

Array of Active Record objects corresponding to Mobile phones and Cars nodes.

Getting all descendants of a node

Using NestedSetBehavior::descendants():

Result:

Array of Active Record objects corresponding to iPhone, Samsung, X100, C200 and Motorola.

Getting all children of a node

Using NestedSetBehavior::children():

Result:

Array of Active Record objects corresponding to iPhone, Samsung and Motorola.

Getting all ancestors of a node

Using NestedSetBehavior::ancestors():

Result:

Array of Active Record objects corresponding to Samsung and Mobile phones.

Getting parent of a node

Using NestedSetBehavior::parent():

Result:

Array of Active Record objects corresponding to Cars.

Getting node siblings

Using NestedSetBehavior::prev() or NestedSetBehavior::next():

Result:

Array of Active Record objects corresponding to Mercedes.

Getting the whole tree

You can get the whole tree using standard AR methods like the following.

For single tree per table:

For multiple trees per table:

Modifying a tree

In this section we'll build a tree like the one used in the previous section.

Creating root nodes

You can create a root node using NestedSetBehavior::saveNode(). In a single tree per table mode you can create only one root node. If you'll attempt to create more there will be CException thrown.

Result:

- 1. Mobile Phones
- 2. Cars

Adding child nodes

There are multiple methods allowing you adding child nodes. To get more info about these refer to API. Let's use these to add nodes to the tree we have:

Result:

- 1. Mobile phones
    - 3. Audi
    - 4. Ford
    - 5. Mercedes
- 2. Cars

Logically the tree above doesn't looks correct. We'll fix it later.

Result:

- 1. Mobile phones
    - 3. Audi
    - 4. Ford
    - 5. Mercedes
- 2. Cars
    - 6. iPhone
    - 7. Samsung
    - 8. Motorola

Result:

- 1. Mobile phones
    - 3. Audi
        - 9. С200
        - 10. X100
    - 4. Ford
    - 5. Mercedes
- 2. Cars
    - 6. iPhone
    - 7. Samsung
    - 8. Motorola

Modifying a tree

In this section we'll finally make our tree logical.

Tree modification methods

There are several methods allowing you to modify a tree. To get more info about these refer to API.

Let's start:

Result:

- 1. Mobile phones
    - 6. iPhone
    - 7. Samsung
        - 10. X100
        - 9. С200
    - 8. Motorola
- 2. Cars
    - 3. Audi
    - 4. Ford
    - 5. Mercedes

Moving a node making it a new root

There is a special moveAsRoot() method that allows moving a node and making it a new root. All descendants are moved as well in this case.

Example:

Identifying node type

There are three methods to get node type: isRoot(), isLeaf(), isDescendantOf().

Example:

Useful code

Non-recursive tree traversal