MongoDB Document Modeling
When do you embed documents vs reference them in MongoDB (or document stores)?
Answers use simple, clear English.
Quick interview answer
Embed when data is accessed together, has a bounded size, and a clear ownership hierarchy (order + line items). Reference when data is shared, large, or independently updated (users referenced by many orders). Avoid unbounded arrays that grow forever.
Detailed answer
Embed when data is accessed together, has a bounded size, and a clear ownership hierarchy (order + line items). Reference when data is shared, large, or independently updated (users referenced by many orders). Avoid unbounded arrays that grow forever.
Real example & use case
Order embeds line items; product catalog is referenced by SKU to avoid duplicating mutable product descriptions everywhere.
Pros & cons
Pros of embed: single read. Cons: document size limits and duplication. References need more round-trips or $lookup.