Unless you've made some major core changes, the problem is that there are only 4 types of entities in Elgg: Object, User, Group, and Site.  You probably want:

elgg_get_entities_from_relationship(array(

'relationship' => 'member_of_treeboo_buyers_groups',

'relationship_guid' => get_loggedin_userid(),

'inverse_relationship' => FALSE,

'types' => 'group',

'subtypes' => 'buyers_group',

'limit' => ELGG_ENTITIES_NO_VALUE  // use this to mean "no limit"

));

Note the 'types' and 'subtypes' options.

Hi, thanks for your reply... 
at the moment it still don't work... i've also made a patch to your code because buyers_group is an "object" and not a "group", but it still give no results...

After investigating i think it's a problem with the object type 'buyers_group',
for example, if i execute this method

elgg_get_entities_from_relationship(array(
'relationship' => 'member_of_treeboo_buyers_groups',
'inverse_relationship' => TRUE
)); 

wich return me a list of user, it works correctly, while if i execute this

elgg_get_entities_from_relationship(array(
'relationship' => 'member_of_treeboo_buyers_groups',
'inverse_relationship' => FALSE
)); 

wich return me a list of buyers_group, it give me no results...
i've defined buyers_group in this way:

add_subtype("object", "buyers_group");
register_entity_type('object','buyers_group');

i'm doing something wrong???

Luca

There is no type 'buyers_group.'  That is the subtype.

It's difficult to help debug when we can't see how your code is creating these groups and relationships...

Hi, you are right! it's a misunderstand due to my bad english, sorry... :)

by the way, after debugging the core elgg files i've found the problem.
Elgg core function elgg_get_entities_from_relationship always do a join on the metadata table. my subtype buyers_group still have no metadata (it's in an early phase of development), so it give no results!!! i attach some metadata to it and all goes right! :)

calling 

elgg_get_entities_from_relationship(array(
'relationship' => 'member_of_treeboo_buyers_groups',
'inverse_relationship' => FALSE));

produce the following query:

SELECT DISTINCT e.* FROM elgg_entities e  JOIN elgg_entity_relationships r on r.guid_two = e.guid  JOIN elgg_metadata n_table on e.guid = n_table.entity_guid  WHERE  (r.relationship = 'member_of_treeboo_buyers_groups') AND  (e.site_guid IN (1)) AND ( (1 = 1)  and e.enabled='yes') ORDER BY e.time_created desc LIMIT 0, 10

can it be considered a bug of elgg? if so, i'll post it...

thanks for your patience!

bye
Luca

elgg_get_entities_from_relationship() does call elgg_get_entities_from_metadata() which seems unnecessary. Could you open a ticket in Trac for this: http://trac.elgg.org/ ?

Ok! i've just opened the ticket...

http://trac.elgg.org/ticket/2274

Bye!
Luca

Hi Cash,

I think that if you want to have both relationship and metadata constraints on a query it is necessary.

I'm pretty sure that one of my plugins counts on this current workflow in fact.

I would hate it if we ended up introducing a new bug to fix the current problem.

Isn't the actual problem that elgg_get_entities_from_metadata() does not work properly if no metadata is attached to an object?

I'm with Kevin here. I'm quite sure one of my plugins is also getting entities based on both metadata and relationship.

i agree too, if elgg_get_entities_from_metadata() could be fixed would be great, but at the moment, even if it's not a big problem, the behaviour of elgg_get_entities_from_relationship is inconsistent and this thing should be at least documented.