Onecomment

Onecomment restricts users to posting only one comment per node.

Perhaps you have a petition content type, which users should only be able to sign once? Onecomment allows you to ensure this. There is real power here when combined with fieldable comments - for example, you could have an event type, where the comment consists of a RSVP status field (like on Facebook: attending / not attending / maybe) - you can use onecomment so that users have a single RSVP status attached to a node.

This is enabled per node type (it is not enabled by default for any of them). Users can be given the 'Post multiple comments on nodes' permission to get round this restriction. Anonymous users are given this permission by default, since the module restricts by user ID, so only one anonymous comment could be made otherwise.

Configure onecomment's settings alongside the comment settings for each node type. Administrators have the option to enable the restrictions and to either hide the form to add comments entirely, or to show the user's existing comment (if they have one) within the comment form. This nicely combines with the 'edit own comments' permission to allow users to quickly edit their sole comment on a node.

Future development

As the Reply module looks like it could be the (distant?) future of Drupal's comment system (see #731724: Convert comment settings into a field to make them work with CMI and non-node entities, the concepts that Onecomment was built for should be introduced to Reply. A patch for reply would replace Onecomment, or Onecomment should be replaced by an additional contrib module that would extend Reply in a similar way to how it currently works. It could even just be an 'example' module for extending Reply -- perhaps even just a good use case example for certain Reply hooks (that may yet need to be added to Reply).
Work is also generally required in promoting the concepts that Onecomment grew up out of -- namely using fieldable comments without bodies, and limiting the number of comments per user on a node. The best first step may be to help push Reply towards being the replacement for core's comment system, as it probably isn't a shoe-in yet.

About the Developers

This project is currently maintained by developers at ComputerMinds - visit us at http://www.computerminds.co.uk. We at ComputerMinds pride ourselves on offering quality Drupal training, Drupal development and Drupal consulting. Go Drupal!