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So I am creating a model for a forum. Think thread and a bunch of comments where. Thread has many comments. In RDBMS world, I would design this as such

Thread --has many--> Comment
id                   id
user_id              thread_id
                     user_id

Now, I guess, with this, the data/schema would follow one of the many normal forms (I forgot which). And I think this is the most sensical way to do it. However, when it comes to doing this in NoSQL world (MongoDB), what would be the best way to design this relationship? I could almost do it in the RDBMS way, but I would lose the advantage of using embedded object. For some reason, I am more inclined to do it like

Thread
_id
user_id
comments => [{_id, user_id, body, created_at}]

What would be the most sensical way to do this I guess that's what I am asking. And why?

denniss
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2 Answers2

6

First off, I hope you have read the docs on Schema Design, which explains with an example similar to yours.

So, you can embed or link according to your choice. I would embed if the number of comments are expected to be manageable (relatively smaller) and link if there would be too many comments.

Embedding has the advantage that only one single DB call is required to show a single post/thread and most usually can send just the mongodb response to the browser as is (if client side does the UI rendering). *Note: And adding a comment will require an UPDATE using $push. And do remember that the comment._id has to be created by you, MongoDB won't auto-create it for you. Any updates of comment data in embedded scenario will require an UPDATE with the $ positional operator.*

rsmoorthy
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-1

In Such cases mongoDB commenting is not as self explanatory as any other RDBMS. As you know MONGODB not a RDBMS at all. Also as it is serialize data storage system you need put comment on every update , whatever you are using as backend technology its PHP/ASP/JAVA or NODE.

db.collection.find( { <query> } )._addSpecial( "$comment", <comment> )
db.collection.find( { <query> } ).comment( <comment> )
db.collection.find( { $query: { <query> }, $comment: <comment> } )

Also please follow the link

https://docs.mongodb.com/manual/reference/operator/meta/comment/

Remember one thing Mongo DB Jason array will act like this as follow with you example 

comments => [{_id, user_id, body, created_at}]
comments => [{_id, body, created_at}]
comments => [{_id, user_id, body }]

etc ... Use it accordingly ...

WebguruInfosystems
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  • In this case, the question is asking how to go about designing a comments schema in MongoDB. What you're describing is how to add comment metadata to documents in a collection. – villecoder Jul 08 '20 at 13:44