Model Tree Structures with Child References
Data in MongoDB has a flexible schema. Collections do not enforce document structure. Decisions that affect how you model data can affect application performance and database capacity. See Data Modeling Concepts for a full high level overview of data modeling in MongoDB.
This document describes a data model that describes a tree-like structure in MongoDB documents by storing references in the parent-nodes to children nodes.
The Child References pattern stores each tree node in a document; in addition to the tree node, document stores in an array the id(s) of the node’s children.
Consider the following hierarchy of categories:
The following example models the tree using Child References, storing the reference to the node’s children in the field
The query to retrieve the immediate children of a node is fast and straightforward:
You can create an index on the field
childrento enable fast search by the child nodes:
You can query for a node in the
childrenfield to find its parent node as well as its siblings:
The Child References pattern provides a suitable solution to tree storage as long as no operations on subtrees are necessary. This pattern may also provide a suitable solution for storing graphs where a node may have multiple parents.