One-to-many referencing pattern in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the one-to-many referencing pattern in MongoDB?

It is a way to link one document to many other documents by storing references (usually ObjectIds) in the related documents instead of embedding all data in one place.

beginner

Why use referencing instead of embedding in a one-to-many relationship?

Referencing keeps documents smaller and avoids duplication. It is useful when the 'many' side can grow large or changes often, so you don't store all data inside one document.

beginner

How do you store references in MongoDB for one-to-many relationships?

You store the ObjectId of the 'one' document inside the 'many' documents as a field, like 'authorId' in posts pointing to an author document.

intermediate

What MongoDB operation helps to get related documents using references?

The $lookup aggregation stage lets you join documents from two collections using references, similar to a SQL join.

beginner

Give an example of a one-to-many referencing pattern in MongoDB collections.

A 'users' collection with user documents, and a 'posts' collection where each post has a 'userId' field referencing the user who wrote it.

In MongoDB, where do you store the reference in a one-to-many relationship?

A In a separate collection only

B In the 'many' side documents

C In the 'one' side document

D You embed all data in one document

The reference is stored in the 'many' side documents to point back to the 'one' side document.

Which MongoDB feature allows combining data from two collections using references?

A $match

B $project

C $group

D $lookup

$lookup is used to join documents from different collections based on references.

Why might you choose referencing over embedding in MongoDB?

A Because referencing is faster for all queries

B To store all data in one place

C To keep documents small and avoid duplication

D Because embedding is not supported

Referencing helps keep documents smaller and avoids duplicating data when the 'many' side is large or changes often.

What type of value is typically used as a reference in MongoDB?

A ObjectId

B String

C Integer

D Boolean

ObjectId is the standard unique identifier used as a reference between documents.

In a blog app, where would you store the author reference for each post?

A Inside each post document as 'authorId'

B Inside the author document as a list of posts

C In a separate collection unrelated to posts

D You embed the entire author document inside each post

Each post stores the 'authorId' to reference the author document, following the one-to-many referencing pattern.

Explain the one-to-many referencing pattern in MongoDB and why it is useful.

Think about how to link one document to many others without copying all data.

Describe how you would retrieve related documents in MongoDB using the one-to-many referencing pattern.

Consider how to combine data from two collections based on stored references.