I'm struggling to see the metadata relationship between groups and discussion topics? I can see that when a new topic is saved the group is set as its container_guid, but I don't think this helps at all.

I'm leaning towards overriding or extending the discussion/save action, creating a relationship between the topic and the group and then searching with elgg_get_entities_from_relationship_count().

Does this sound reasonable? Or am I missing something obvious with the metadata?

Thanks

No, I think Pawel meant that you can search groups based on the "forum_enable" metadata.

$groups = elgg_get_entities_from_metadata(array(
    'type' => 'group',
    'metadata_name_value_pairs' => array(
        'name' => "forum_enable"
        'value' => "no",
        'operand' => '!='
    ),
    'limit' => false
));

This will return all groups that have group discussions enabled.

I see. Thanks.

Although I still can't see how you could order the results based on the number of topics, as they are not stored as metadata? I think you may still need a JOIN (or something!) to do that? 

I've actually done it my way now, it was quite simple and I think it makes the ordering easier. It also means that results will only show up if at least one discussion topic has been created.

@Juho Jaakkola :) There is another CSS trick.

I meant create CSS style and add link class into  menu:item.

In css.php

.elgg-menu-page li.elgg-state-selected > a {
    color: white;
}

.elgg-menu-page li > a.elgg-state-selected {
    color: black;
}

Sure, it's works for menu:page only.

For other items need to create similar styles too, e.g.:

.elgg-menu-extras li > a.elgg-state-selected {
    color: white;
}
.elgg-menu-extras li.elgg-state-selected > a {
    color: black;
}

Make all your plugin pages push a context like "vendor_myplugin". Give your site menu item the same name.

Elgg has a built-in menu handler that will auto-select the item based on current (topmost) context.

Thanks for the answers everyone.

For clarity, if anyone else has the same question in the future:

My menu item was setup using

$item = new ElggMenuItem('item_name', elgg_echo('Menu Label'), 'plugin/link');
elgg_register_menu_item('site', $item);

Then on each plugin page where I want to highlight that menu item I used

elgg_push_context('item_name');

Seems to work anyway!