Storing “votes” in a database

Question

I\'m writing what will be an intranet application, and one of its features is roughly analogous to content voting - not unlike what SO, Amazon, and many other sites do.

Answer 1

I'd say you need to figure out how these votes will be used and design specific queries for your data model first. This is not necessarily SQL model. If you're coming from SQL world, passing through official MongoDB tutorial helps to clear the mind for the start.

For example, if you only need to store and display votes for a single issue page, it may be convenient to store votes in a single string field of the issue, which will look like id1:id2:id3:. Assuming all ids are of the same length, there are some interesting properties:

1. Count all votes for the issue:

   len(issue.votes)/len(id)

2. Find I voted on the issue

   myid in issue.votes

3. Find all issues you voted on:

   select issue.id from issues where issue.votes contains(myid)

4. Find the most voted issues

   select issue.id from issues order by len(issue.votes) desc limit 10

This architecture allows to avoid expensive calculations on read in these specific cases, but updating issue.votes on vote might be more expensive than adding a row in a table. In this case 100 votes with 4 bytes per id + separator is 500 bytes string. In your proposed variant 100 votes are 800 bytes.

Disclaimer: I never implemented anything like this, it is just an idea.