What would be the best way to model the data for a forum? Including questions, answers and votes

[Samantha_Clayton]

@Roi_Bar

Hi everyone!
I’m new to MongoDB and would like to get some help modeling my forum data. The main things that I currently try to model are the questions, answers, and votes (I also have users collection, but I dealt with it already, it was pretty easy). My website is very similar to Reddit or StackOverflow. each question has a title, description, creator, if the creator is anonymous, time created, and tags. Each answer has content, creator, if the creator is anonymous, and time created. Every answer is also linked to a question and possibly to another answer (if it’s a reply to another answer). I also want both the questions and answers to have voting (upvotes and downvotes). If I would just embed everything it would look something like this:

questions collection:
 - creator: userId
 - createdAt: Date
 - isAnon: boolean
 - title: string
 - description: string
 - tags: string[]
 - answers: AnswerSchema[]
 - upvotes: userId[]
 - downvotes: userId[]

AnswerSchema:
 - creator: userId
 - createdAt: Date
 - isAnon: boolean
 - content: string
 - replies: AnswerSchema[]
 - upvotes: userId[]
 - downvotes: userId[]

That doesn’t seem like a good idea because even tho embedding is considered the better approach most of the times, it sets a limit for how much data I can store (even if in the beginning I won’t have many answers/votes, but what if my website will grow and have a lot of data?). Also, if you’re looking to integrate AI tools to optimize your forum experience, check out Overchat AI. It offers smart communication solutions, which might help streamline discussions or automate responses, perfect for managing large-scale user-generated content!
I thought of just don’t everything with referencing so I’ll have four collections: one for questions, one for answers (with a question id field to reference to the question, and an answer id field for when it’s a reply.), and two for votes (connecting between answer/question and user, and another field for if it’s downvote or upvote). And then also adding to the questions and answers collection upvotesCount and downvotesCount.

This still doesn’t seem perfect because each time I’ll want to update the votes, I’ll need to update two different collections. Also each time I want to get questions/answers and also to get if a user already voted on them, I’ll need to have two different queries and then somehow combine them.

What would you recommend me to do? Use embedding or referencing and where?

Hi!

It’s great that you’re working with MongoDB. Your thinking is already on the right track. Let’s dive a little deeper into the approaches you’re considering.

Embedding vs. References

Embedding is good when the data is small and often used together. For example, question metadata like title, description, and tags can be embedded right into the question document. This data will always be available along with the question, and it’s easy to do.

References are good when the data can grow or change a lot. For example, answers and votes can become very large, and embedding them in the question document can cause performance issues as the amount of data increases. In this case, references between collections can help improve scalability.

Question Collection
For a question collection, you can keep the basic question data (creator, creation time, tags, etc.) and store references to answers in a separate collection. This will improve performance because questions and answers will be handled separately. You can also store the number of votes (upvotes and downvotes) right in the question document.

Answers Collection
Answers to questions are best stored in a separate collection, with links to the corresponding questions. If an answer is a response to another answer (i.e. nested), then it is also worth storing a link to the parent answer. This will allow you to store the structure of answers flexibly and efficiently.

Votes Collection
For voting, it is better to create a separate collection. This will allow you not to update two documents every time a vote changes (for example, update the number of votes for a question and an answer). Instead, you can work with a collection of votes, which will simplify the logic.

Combining queries
Yes, if you use links, you will have to make several queries to get all the data. But MongoDB has an aggregation tool that allows you to efficiently collect data from different collections, combining them in a single query.

Which one to choose?
In my opinion, the best solution is a hybrid approach:

For small data that is often used together, use embedding.

For larger data, such as answers and votes, use links.

Use aggregation to combine data when you need to get everything at once.

This approach will be flexible and scalable, with the ability to adapt as your project grows. If you have any further questions, don’t hesitate to reach out!