Database Architecture for “Badge” System & Arbitrary Criteria (MySQL/PHP)

badgedatabase-design

Quickie-Question:

To summarize, I'm a little confused as to how I would design such a database that allows indefinite badge-rule creation without requiring structural changes to the previously existing user-tables in the database.

Storing Badge Title, Criteria, etc. What would that Table look like?

  • badge_id (1)
  • badge_title (10K Badge)
  • badge_image (10k.jpg)
  • badge_criteria ([posts] >= 10000)
    ...

Winded-Question:

I would like to implement a badge-system on my own personal projects, but am seeking a bit of advice as to how one would best do such a thing. I've been reading some of the questions here about badge-systems, but don't see the database-architecture getting much attention.

Badges that are based on user-points (Hypothetical "10k Badge") would seem pretty straight forward. Any event that affects the users reputation (upvotes, downvotes, answer-accepted, etc) would invoke a method to review the users new reputation, and potentially award a badge.

That system sounds pretty straight forward, but what does that look like as a database for the administrator who wants to create innumerable amounts of badges with little-effort down the road – some of which may be based on different criteria, and not simply the user reputation.

User-reputation is likely a value within the user-record itself. But ideally, wouldn't you want to avoid having to add new fields to the user table when you create new badges? For instance the "Edited 100 Entries" badge – you wouldn't create a new column "entries_edited" within the Users Table, would you? And then increment that after each entry-edited…

Any hints?

Stackoverflow Archive:


Note: I'm NOT asking how to associate badges with users. I'm NOT asking how to award badges (that will be done programmatically)

Best Solution

Given that the badge criteria can be arbitrarily complex, I don't think you can store it in a database table broken down into "simple" data elements. Trying to write a "rules engine" that can handle arbitrarily complex criteria is going to take you down the path of basically re-writing all the tools that you have in your programming language.

If you know in advance you want the badges limited to only certain fields (i.e. badges are only based off reputation or number of edits or something), then you can store those in a simple table like:

ReputationBadgeCriteria
  BadgeId
  BadgeName
  MinReputation

Alternatively, you could use some kind of DSL to write your "rules" but you end up having to also create a parser to parse the rules when you read them as well as something to execute these rules. Depending on the complexity you want in your DSL, this may not be a trivial task. This looks like the path you are going in your question with having a Criteria column (presumably plain text) that has something like "[Reputation] > 1000" or "[Posts] > 5" in it. You still have to parse and execute those rules and the complexity of writing something to do so is dependent on how complex you want those rules to be.

I would recommend you read these Daily WTF articles for information on why this approach leads to pain.

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