How do you design a schema for tree structures in MongoDB

Question

Can you tell me How do you design a schema for tree structures in MongoDB?

Answer 1

Designing a schema for tree structures in MongoDB depends on how you need to traverse and query the data. Here are some common approaches:

1. Parent-Reference Model (Adjacency List)

Each node stores a reference to its parent.

Schema Example:

{

  "_id": ObjectId("1"),

  "name": "Node A",

  "parent": ObjectId("null")  // Root node (no parent)

}

{

  "_id": ObjectId("2"),

  "name": "Node B",

  "parent": ObjectId("1")  // Child of Node A

}

2. Child-Reference Model

Each parent node keeps an array of references to its children.

{

  "_id": ObjectId("1"),

  "name": "Node A",

  "children": [ObjectId("2"), ObjectId("3")]

}

3. Materialized Path

Each node stores the full path as a string.

{

  "_id": ObjectId("1"),

  "name": "Node A",

  "path": "1"

}

{

  "_id": ObjectId("2"),

  "name": "Node B",

  "path": "1/2"

}

4. Nested Set Model

Each node has left and right values representing its position in a pre-ordered traversal.

{

  "_id": ObjectId("1"),

  "name": "Node A",

  "left": 1,

  "right": 6

}

{

  "_id": ObjectId("2"),

  "name": "Node B",

  "left": 2,

  "right": 3

}

5. Closure Table Model (Hybrid Approach)

Stores parent-child relationships in a separate collection.

{

  "_id": ObjectId("1"),

  "ancestor": ObjectId("1"),

  "descendant": ObjectId("2"),

  "depth": 1

}