How can a poster of a comment notify selected users about a new comment?

Question

When I write a comment on a node, I want to be able to select the users that will get a notification (via e-mail) about that new comment. Basecamp has this feature and I think it is very cool.

Is this possible without customization? I know how to notify the author of the comment, but this is different.

Answer 1

When I write a comment on a node, I want to be able to select the users that will get a notification about that new comment.

1) Download Rules and Entity Reference Modules.

2) Enable Rules, Rules UI (User Interface, we need this), and Entity Reference

3) In your comment fields

• Add a field with Entity Reference and a widget of Auto complete (tag style)

For example: I named mine lalala (click picture below to enlarge)

4) In your field settings:

• Select User as your target type

After you click save field settings you are taken to another screen, scroll down and find Number of values and change it to Unlimited and Save Changes.

5) Add a new rule by going to /admin/config/workflow/rules/reaction/add

• React on Event: After Saving New Comment
• Restrict by Type: Select your content type (In this example it's Article Comments, since in Articles Comments is where I put my lalala field.)

6) Click on Add a Loop

• Data selector: comment:field-lalala (remember I named my entity reference field lalala)

7) Click Add Action, but the one from the loop!

8) Select Fetch Entity by Property

• Entity Type: User
• Property: Email
• Data Selector: list-item:mail
• Limit Result Count: put a large number here in case it has an effect. (since we are looping, I don't believe so, but I am not 100% sure)

9) Add another action to the loop, this time add Send Mail

Click on switch to data selection button.

To: list-item:mail

The end result should look like this

Now add a new comment.

On your entity reference field since we are using Autocomplete (tag style) you start to type a user name and select the user. Then add a comma , to add more users

Ex:

After posting the comment, all referenced users should receive an e-mail.

Answer 2

To my knowledge this is NOT possible only usiing Drupal core, so you'll have to do some "customization". So far the bad news ... The good news is that you can use the Rules module to create a rule to send such notifications.

However the challenge in your question is "which users should get the notifications". If you'd have dozens, or hundreds (or thousands?) of users, using something like a select list doesn't seem like an option to me. Therefor I'd recommend you to use the Flag module to have each user indicate something like "Notify these users whenever I post comments" (using so called "private" flags).

With both Rules and Flag in place, it's a piece of cake to then send notifications of comments that get posted to the users flagged by the author of the comment. To do so, I'd recommend you to also have a look at the Community documentation about the Message Stack, which allows you to do way more then just "sending an eMail".

The previous approach will always send such notifications to the same set of (flagged) users, for each comment posted by a single user. Unless the list of flagged users is adapted before posting a new comment (by flagging more users, or unflagging some previously flagged users). However, by also using the Flag Lists module you could make this more flaxible. I.e. each user can create his/her own set of flags (similar to "Google circles"?). Some more details about Flag Lists (from its project page):

Flag lists allows regular users to create unlimited private flags called lists. Flag lists extends Flag. In Flag, a site administrator creates the flags that any authorized users may use. In Flag lists, users create their own lists, and they may only add to their own lists.