Embedding: One-to-Few Relationships

Embedding means storing related data directly inside a parent document rather than in a separate collection. Instead of linking two collections with a foreign key, you nest the related data as a sub-document or an array of sub-documents. This is MongoDB's most powerful design tool because it allows a single read to retrieve the parent and all its related data at once.

A one-to-few relationship exists when one parent document has a small, bounded number of child items—typically fewer than a few dozen. Classic examples include a blog post and its comments, a user and their addresses, or an order and its line items. When the child count is predictable and small, embedding is almost always the right choice.