Hi, Nowadays you cannot define a calculated attribute as identifier of an entity. If you need to check the uniqueness of both the values of tree and stem id, what you You can do is to define a Custom check for both **both** `tree_id` and `stem_id` attributes. The solution looks a bit tricky and as the expression will be this: `count(parent()/tree[tree_id = $this/parent()/tree_id and stem_id = $this/parent()/stem_id]) = 1` This expression means that you key identifiers for the count of trees having `tree_id` and `stem_id` equal to the ones of the current row must be equal to 1. ![alt text][1] `tree` entity. Please try it and let us know. Thanks, Open Foris Team [1]: http://www.openforis.org/support/upfiles/tree_id_and_stem_id_uniqueness_validation.pngTeam

Hi, Nowadays you cannot define a calculated attribute as identifier of an entity. If you need to check the uniqueness of both the values of tree and stem id, what you can do is to define a Custom check for both `tree_id` and `stem_id` attributes. The solution looks a bit tricky and the expression will be this: `count(parent()/tree[tree_id = $this/parent()/tree_id and stem_id = $this/parent()/stem_id]) = 1` This expression means that you the count of trees having `tree_id` and `stem_id` equal to the ones of the current row must be equal to 1. ![alt text][1] Please try it and let us know. Thanks, Open Foris Team [1]: http://www.openforis.org/support/upfiles/tree_id_and_stem_id_uniqueness_validation.png