asked 3 months ago
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I'm designing a schema for a blog platform. I have posts, comments, and users. I can't figure out when to embed vs reference:
What are the rules of thumb here?
One pattern I've seen work well: embed a summary in the parent, store the full data separately.
// post document
{
title: "...",
commentCount: 47, // ← embedded count for fast display
topComment: { ... }, // ← embedded "best" comment for preview
// full comments are in a separate collection
}This gives you fast list-page rendering (no join needed) while keeping the document size bounded.
The classic MongoDB mantra: embed when you read together, reference when you read separately.
For your blog case:
The 16MB document size limit is a hard constraint. At ~1KB per comment, you'd hit it at ~16K comments/post. Use a separate collection for anything unbounded.
For your specific schema:
users → reference from everythingcomments → separate collection, indexed on postId1
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