If you are upgrading from any 3.x version before alpha6, I recommend reading the alpha6 release notes! Major changes occurred in that release.
This is the successor of Corresponding Node References, so a shout-out goes to everyone who ever worked on it!
CER keeps reference fields in sync. If you have two entities that refer to each other using Entity Reference (or some other kind of reference field), it saves you the trouble of double-editing your entities in order to have them point at each other. If entity Alice references entity Bob, CER will make Bob reference Alice, and keep the references up-to-date when either entity is updated or deleted.
- 7.x-3.x (alpha) depends on CTools, Entity API and Elements.
- 7.x-2.x depends only on Entity Reference.
- Prefer 3.x. It's the active development branch and is a quantum leap over 2.x, featuring a better UI, support for field collections, and native support for other field types besides Entity Reference. It includes add-on modules to integrate with Drupal Commerce and Profile2, as well as a module to override CER settings for individual entities.
- 2.x is now deprecated, and once there is a stable 3.x release, it will be retired. The only real reason to use it is if you have 1.x and fear database updates -- 2.x does not change the database in any way, so you can drop it in over 1.x safely and easily revert if you run into problems. 2.x's main improvement over 1.x is that it has proper support for Entity Reference fields that use Views as a backend.
CER 1.x is no longer supported. If you're still using it, you should update to 3.x.
Upgrading from CNR?
No worries -- CER will automatically detect the presence of CNR, take over its functionality, and disable it. Easy-peasy.
This module has been sponsored by Digital Loom.