When should I embed vs reference in MongoDB?
Embed when data is small, always read with the parent, and rarely accessed independently (a user's address). Reference when data is large, shared (a post's author), or frequently accessed independently (comments on a post).
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More FAQs in How to Handle Relationships in MongoDB With Mongoose ref and populate
Use ref to store ObjectId references for large or shared data, and populate to fetch related data. Embed small, always-read-together data directly in the document. Choose based on data size and access patterns.
Embed stores related data directly in the document (fast reads, duplication). Reference stores the related document's id, requiring populate to fetch it. Embed for small always-read-together data; reference for large or shared data.
populate tells Mongoose to fetch the referenced document. Post.find().populate('author') runs a second query to fetch the author for each post, similar to a SQL join. This is how you get related data when using references.
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