What is the N+1 query problem with populate in Mongoose?
Calling populate per item in a loop instead of on the find query. This causes N+1 queries instead of one. For lists, call populate once on the find query; Mongoose batches it efficiently, avoiding the N+1 problem.
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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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