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Trees

MongoDB lends itself quite well to storing hierarchical data. This chapter will demonstrate some examples!

Full Tree in Single Document 

<?php#[Document]class BlogPost{    #[Id]    private string $id;    #[Field(type: 'string')]    private string $title;    #[Field(type: 'string')]    private string $body;    /** @var Collection<int, Comment> */    #[EmbedMany(targetDocument: Comment::class)]    private Collection $comments;    // ...}#[EmbeddedDocument]class Comment{    #[Field(type: 'string')]    private string $by;    #[Field(type: 'string')]    private string $text;    /** @var Collection<int, Comment> */    #[EmbedMany(targetDocument: Comment::class)]    private Collection $replies;    // ...}

Retrieve a blog post and only select the first 10 comments:

<?php$post = $dm->createQueryBuilder(BlogPost::class)    ->selectSlice('replies', 0, 10)    ->getQuery()    ->getSingleResult();$replies = $post->getReplies();

You can read more about this pattern on the MongoDB documentation page "Trees in MongoDB" in the Full Tree in Single Document section.

Parent Reference 

<?php#[Document]class Category{    #[Id]    private string $id;    #[Field(type: 'string')]    private string $name;    #[ReferenceOne(targetDocument: Category::class)]    #[Index]    private ?Category $parent = null;    // ...}

Query for children by a specific parent id:

<?php$children = $dm->createQueryBuilder(Category::class)    ->field('parent.id')->equals('theid')    ->getQuery()    ->execute();

You can read more about this pattern on the MongoDB documentation page "Trees in MongoDB" in the Parent Links section.

Child Reference 

<?php#[Document]class Category{    #[Id]    private string $id;    #[Field(type: 'string')]    private string $name;    /** @var Collection<int, Category> */    #[ReferenceMany(targetDocument: Category::class)]    #[Index]    private Collection $children;    // ...}

Query for immediate children of a category:

<?php$category = $dm->createQueryBuilder(Category::class)    ->field('id')->equals('theid')    ->getQuery()    ->getSingleResult();$children = $category->getChildren();

Query for immediate parent of a category:

<?php$parent = $dm->createQueryBuilder(Category::class)    ->field('children.id')->equals('theid')    ->getQuery()    ->getSingleResult();

You can read more about this pattern on the MongoDB documentation page "Trees in MongoDB" in the Child Links section.

Array of Ancestors 

<?php#[MappedSuperclass]class BaseCategory{    #[Field(type: 'string')]    private string $name;    // ...}#[Document]class Category extends BaseCategory{    #[Id]    private string $id;    /** @var Collection<int, Category> */    #[ReferenceMany(targetDocument: Category::class)]    #[Index]    private Collection $ancestors;    /** @var Collection<int, Category> */    #[ReferenceOne(targetDocument: Category::class)]    #[Index]    private ?Category $parent = null;    // ...}#[EmbeddedDocument]class SubCategory extends BaseCategory{}

Query for all descendants of a category:

<?php$categories = $dm->createQueryBuilder(Category::class)    ->field('ancestors.id')->equals('theid')    ->getQuery()    ->execute();

Query for all ancestors of a category:

<?php$category = $dm->createQuery(Category::class)    ->field('id')->equals('theid')    ->getQuery()    ->getSingleResult();$ancestors = $category->getAncestors();

You can read more about this pattern on the MongoDB documentation page "Trees in MongoDB" in the Array of Ancestors section.

Materialized Paths 

<?php#[Document]class Category{    #[Id]    private string $id;    #[Field(type: 'string')]    private string $name;    #[Field(type: 'string')]    private string $path;    // ...}

Query for the entire tree:

<?php$categories = $dm->createQuery(Category::class)    ->sort('path', 'asc')    ->getQuery()    ->execute();

Query for the node 'b' and all its descendants:

<?php$categories = $dm->createQuery(Category::class)    ->field('path')->equals('/^a,b,/')    ->getQuery()    ->execute();

You can read more about this pattern on the MongoDB documentation page "Trees in MongoDB" in the Materialized Paths (Full Path in Each Node) section.