Reverse nodereference

One thing is the ability to display a list of back references in the referred nodes.

Here, I would like to add to the list of existing solutions the Node Relationships module. It allows you to show back references in the referred nodes using dynamically configured views that you can extend to suit your needs. You can display these views using several methods in the node view, including one the turns this view into a CCK field that you can place wherever you wish in the "Manage fields" screen.

I added this feature to Node Relationships because other solutions require you to duplicate relationship related data, which is IMHO bad design, because it's a source of possible database inconsistencies and increased cost to maintain relationships to keep them in sync.

CCK was recently enhanced to automatically create indexes for the node reference columns, so the joins implied here can take advantage of this.

Another thing is reverse relationships in Views. This is a bit more complex that it seems. This kind of relationships should allow you to create joins from referred to referrer nodes. This has been discussed on the CCK issues queue: Reverse node-reference views relationship. In summary: in order to avoid duplicate records when the referrer nodes support revisions, then a nested join can help, but this is not supported until MySQL 5.1. It would be nice to figure out a different method to solve this using pure SQL, and then try to find its way into Views.