Embedded Documents in MongoDB: Document Design Best Practices

What Are Embedded Documents?

Embedded documents are documents nested inside another MongoDB document. They represent related data stored together in a single BSON document.

This contrasts with referenced documents, where related data is stored in separate documents and linked by references.

• Stored as nested JSON objects within a parent document.
• Allow atomic updates to related data.
• Improve read efficiency by reducing the need for multiple queries.

When to Use Embedded Documents

Choosing to embed or reference data depends on your application's data access patterns and relationships.

Embedding is ideal when related data is frequently accessed together and has a one-to-few relationship.

• Use embedding for data that is mostly read together.
• Embed when the related data size is small and bounded.
• Avoid embedding large arrays that grow unbounded.
• Prefer embedding for one-to-few relationships, not one-to-many or many-to-many.

Advantages and Trade-offs of Embedding

Embedding offers several benefits but also some limitations to consider.

• Advantages:
• - Faster reads by retrieving related data in one query.
• - Atomic updates to the entire document.
• - Simplified data model with fewer collections.
• Trade-offs:
• - Document size limits (16MB max) can be a constraint.
• - Large embedded arrays can degrade performance.
• - Updating embedded data may require rewriting the whole document.

Practical Example of Embedded Documents

Consider a blog application where each post has an author and a few tags. Embedding the author details and tags inside the post document can simplify queries.