Is it possible to create a user group in Joomla 2.5 that includes everyone that is NOT a member of a particular group?

Question

I have two similar pages that need a menu link. Page 1 is shown to members of Group A. Page 2 is shown to everyone who is not a member of Group A. I have a "Guest" group which would include everyone who is not logged in. But some users are members of group A and Group B. I cannot figure out how to only show one link to them, based on whether they are a member of Group A or not. If I create an access level that includes only Group A and one that includes every other group and someone is in both groups, they will see both links, which is redundant since the pages are different versions of the same page. Any ideas?

Answer 1

We've got a similiar situation, and they way we got around it is to have another Usergroup called "GroupNotA". Then, we have a user plugin that we configure the UserGroups that are in play, and use the OnUserAfterSave event to insure everyone is conditionally in the correct user groups as shown in the code snippets below. With that, we can user menu items, etc. that are available to GroupA and GroupNotA.

myUserPlugin.xml

<field name="usergroup_a" type="usergroup" label="Group A" multiple="false" />
<field name="usergroup_not_a" type="usergroup" label="Group Not A" multiple="false" />

myUserPlugin.php

public function onUserBeforeSave($oldUser, $isnew, $newUser)
{
    $UserGroupA = $this->params->get('usergroup_a');
    $UserGroupNotA = $this->params->get('usergroup_not_a');

    if(in_array(UserGroupA, $newUser['groups'])){
        // Use IS in Group A - do nothing?
    }else{
        // Use is NOT in Group A - Add to group $UserGroupNotA
        // add/remove from array $user['groups']
    }

A word of caution though, the natural inclination was to use JUserHelper::addUserToGroup(), but it triggers OnUserAfterSave() again, so we went with direct manipulation of the Groups array.

A sample user plugin is installed with Joomla at plugins/user/example.php, and full documentation is available at Plugin/Events/User. Good Luck.

Note I just realized that we do this during a new user registration, so I'm altering the answer to use the event onUserBeforeSave(). I'm not sure that it will work as I originally suggested or not, but at least you have a starting point and the pieces to accomplish a solution.