How do you model a many-to-many relationship in MongoDB with an example

Question

Can you tell me How do you model a many-to-many relationship in MongoDB with an example?

Answer 1

In MongoDB, a many-to-many relationship can be modeled in a couple of ways. Here are the most common approaches:

1. Using Reference Documents

In this approach, you create separate collections for each of the entities and store references (IDs) to related documents.

Example: Students and Courses

Students Collection:

{

  "_id": ObjectId("student1"),

  "name": "Alice",

  "courseIds": [ObjectId("course1"), ObjectId("course2")]

}

{

  "_id": ObjectId("student2"),

  "name": "Bob",

  "courseIds": [ObjectId("course2"), ObjectId("course3")]

}


Courses Collection:

{

  "_id": ObjectId("course1"),

  "title": "Math 101",

  "studentIds": [ObjectId("student1")]

}

{

  "_id": ObjectId("course2"),

  "title": "History 201",

  "studentIds": [ObjectId("student1"), ObjectId("student2")]

}

{

  "_id": ObjectId("course3"),

  "title": "Science 301",

  "studentIds": [ObjectId("student2")]

}