Photo © Matt Slack, used with permission.

Bi-Directional and Self-Referential Associations in Rails

By Joshua Kovach

I’ve been working on an application that works to match users together based on a complex set of criteria (read: big slow database query and in-memory processing). The core usage of the application revolves around these user matches, so I want to make sure that either the algorithm will run very fast or can be cached so that it’s not run every time a user visits their matches page.

The most important requirement for our matches is reciprocation. To solve this problem and meet all of the requirements, we can create a bi-directional, self-referential, self-syncing, many-to-many association between users using a has_many :through association with a join model to keep track of a user’s matches.