親参照を持つモデルツリー構造

Overview

This page describes a data model that describes a tree-like structure in MongoDB documents by storing references to "parent" nodes in children nodes.

パターン

The 親参照 pattern stores each tree node in a document; in addition to the tree node, the document stores the ID of the node's parent.

以下のカテゴリの階層を考慮します。

The following example models the tree using 親参照, storing the reference to the parent category in the field parent:

db.categories.insertMany( [
   { _id: "MongoDB", parent: "Databases" },
   { _id: "dbm", parent: "Databases" },
   { _id: "Databases", parent: "Programming" },
   { _id: "Languages", parent: "Programming" },
   { _id: "Programming", parent: "Books" },
   { _id: "Books", parent: null }
] )

• The query to retrieve the parent of a node is fast and straightforward:

  db.categories.findOne( { _id: "MongoDB" } ).parent

• You can create an index on the field parent to enable fast search by the parent node:

  db.categories.createIndex( { parent: 1 } )

• You can query by the parent field to find its immediate children nodes:

  db.categories.find( { parent: "Databases" } )

• To retrieve subtrees, see $graphLookup.