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Asked: 2026-05-29T11:33:17+00:00

I’m currently specing out a project that stored threaded comment trees. For those of

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I’m currently specing out a project that stored threaded comment trees.

For those of you unfamiliar with what I’m talking about I’ll explain, basically every comment has a parent comment, rather than just belonging to a thread. Currently, I’m working on a relational SQL Server model of storing this data, simply because it’s what I’m used to. It looks like so:

Id int  --PK
ThreadId int  --FK
UserId int  --FK
ParentCommentId int  --FK (relates back to Id)
Comment nvarchar(max)
Time datetime

What I do is select all of the comments by ThreadId, then in code, recursively build out my object tree. I’m also doing a join to get things like the User’s name.

It just seems to me that maybe a document storage like MongoDB which is NoSql would be a better choice for this sort of model. But I don’t know anything about it.

  • What would be the pitfalls if I do choose MongoDB?
  • If I’m storing it as a Document in MongoDB, would I have to include the User’s name on each comment to prevent myself from having to pull up each user record by key, since it’s not “relational”?
  • Do you have to aggressively cache “related” data on the objects you need them on when you’re using MongoDB?

EDIT: I did find this arcticle about storing trees of information in MongoDB. Given that one of my requirements is the ability to list to a logged in user a list of his recent comments, I’m now strongly leaning towards just using SQL Server, because I don’t think I’ll be able to do anything clever with MongoDB that will result in real performance benefits. But I could be wrong. I’m really hoping an expert (or two) on the matter will chime in with more information.

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1 Answer

  1. Editorial Team

    The main advantage of storing hierarchical data in Mongo (and other document databases) is the ability to store multiple copies of the data in ways that make queries more efficient for different use cases. In your case, it would be extremely fast to retrieve the whole thread if it were stored as a hierarchical nested document, but you’d probably also want to store each comment un-nested or possibly in an array under the user’s record to satisfy your 2nd requirement. Because of the arbitrary nesting, I don’t think that Mongo would be able to effectively index your hierarchy by user ID.

    As with all NoSQL stores, you get more benefit by being able to scale out to lots of data nodes, allowing for many simultaneous readers and writers.

    Hope that helps

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