Feature proposal: Add a `shard_keys` method to ActiveRecord models

This is mostly a replica of a previous discussion from 2020 but hopefully it’s okay to re-open the topic.

It would be useful to have a shard_keys (could be called shards or shard_names) method that returns an array of shards that model can connect to. This would also allow for methods like on_all_shards (to perform an action on each shard) and sharded? (which would return true if the model is configured to connect to shards, otherwise returns false).

I have a working branch that implements all of the above but, given the previous discussion and general guidance to start a topic first, I’m bringing it up here.

The implementation (on connection_handling) looks like so:

def connects_to(database: {}, shards: {})
  @shard_keys = shards.keys

def sharded?

def shard_keys
  connection_class_for_self.instance_variable_get(:@shard_keys) || []

shard_keys gets the ivar from connection_class_for_self so that all descendants of abstract connection classes know which shards they can connect to. connection_class_for_self also returns self, for connection classes themselves, and thus would return their own @shard_keys ivar.

1 Like

If you have a patch, please do open a PR. It is easier to get feedback with the code in place.

Here you go! Add `.shard_keys`, `.sharded?`, & `.on_all_shards` methods to AR Models by HeyNonster · Pull Request #51009 · rails/rails · GitHub

One actioncable integration (3.3)rake test:integration task failed but it looks unrelated?

I’ve rebased the branch to fix some failures due to test fixture changes.

One thing to note, if it’s helpful, we’re using (almost) this exact code in production at Zendesk and it works well for us!