How should I keep my publication reactive?

Question

I am migrating from a custom user rights management system to Alanning:roles v2.0. I have a very basic structure:

• A basic user
• Groups of users, each with specific settings. I store them in a "group" collection.
• A group admin status for users who manage the groups (each group has its group admins).

I was previously storing the group members and admins mongo _id in the "group" document. This way, I could publish the groups reactively : I just had to check if the userId was in the group document, in the "members" or "admins" fields.

Now that I switched to a right management enforced by Alanning:roles, I do something like this in my publication :

const userGroupsAsAdmin = Roles.getPartitionsForUser (this.userId, ['group_admin'])
const userGroupsAsMember = Roles.getPartitionsForUser (this.userId, ['member'])
const selector = {$or:[{'_id':{$in: userGroupsAsMember}},{'_id':{$in: userGroupsAsAdmin}}]}
const options = {}
const response = Groups.find(selector, options)
return response

Note that Roles.getPartitionsForUser () is just the new function name for Roles.getGroupsForUser ().

The problem here is that the publication don't watch for changes in the role collection, so when a user becomes member, the publication isn't updated. I know this is a common issue and I know 3 ways to fix this, but none of them feels satisfying:

• The best candidate: denormalize and duplicate. I keep my members and admins fields in the group document. What bugs me is that I will keep 2 versions of the same thing and create a possibility for inconsistencies to appear.

• Add an argument to the publication and rerun it using this argument (e.g. userGroupsAsMember) but it relies on client and makes it send unnecessary info.

• Use low level publication api, either directly or using a package. I already did this directly in the past but I don't want to rely on Cursor.observe() anymore because it doesn't scale efficiently and create an unnecessary server load.

Am I missing an option? If not, what would be the best way to keep my publication reactive?

Answer 1

Use reywood:publish-composite to create a reactive join.

Meteor.publishComposite("my-groups", {
  find: function() {
      // findOne won't work, it's not a cursor
      return Meteor.users.find(
        {_id: this.userId},
        {fields: {roles: 1}}
      );
    },
  children: [{
    find: function(user) {
      // getPartitionsForUser allows the first parameter to be the actual user object.
      const userGroupsAsAdmin = Roles.getPartitionsForUser (user, ['group_admin']);
      const userGroupsAsMember = Roles.getPartitionsForUser (user, ['member']);
      const selector = {$or:[{'_id':{$in: userGroupsAsMember}},{'_id':{$in: userGroupsAsAdmin}}]};
      const options = {};
      const response = Groups.find(selector, options);
      return response;
    }
  }]
});

Roles.getPartitionsForUser doesn't return a cursor, therefore it can't be reactive. That's why you'll need to publish a Meteor.users.find call, too.