Model Tree Structures with Child References具有子引用的模型树结构¶

Overview概述¶

This page describes a data model that describes a tree-like structure in MongoDB documents by storing references in the parent-nodes to children nodes.本页描述了一个数据模型，该模型通过将父节点中的引用存储到子节点，来描述MongoDB文档中的树状结构。

Pattern模式¶

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.子引用模式将每个树节点存储在文档中；除树节点外，文档还以数组形式存储节点子节点的id。

Consider the following hierarchy of categories:考虑以下类别的层次结构：

The following example models the tree using Child References, storing the reference to the node’s children in the field children:以下示例使用子引用对树进行建模，并将对节点子节点的引用存储在字段children中：

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

• The query to retrieve the immediate children of a node is fast and straightforward:检索节点的直接子节点的查询既快速又简单：

  db.categories.findOne( { _id: "Databases" } ).children

• You can create an index on the field children to enable fast search by the child nodes:您可以在字段children上创建索引，以启用子节点的快速搜索：

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

• You can query for a node in the children field to find its parent node as well as its siblings:可以在children字段中查询节点，以查找其父节点及其同级节点：

  db.categories.find( { children: "MongoDB" } )

The Child References pattern provides a suitable solution to tree storage as long as no operations on subtrees are necessary. 只要不需要对子树进行操作，子引用模式就为树存储提供了合适的解决方案。This pattern may also provide a suitable solution for storing graphs where a node may have multiple parents.该模式还可以为存储一个节点可能有多个父节点的图提供合适的解决方案。