Can somebody explain why these two seemingly identical queries produce different results? Specifically, second result is out of order:

(d/transact conn
            [{:db/id :tg/node-root :children [:tg/node-1]}
             {:db/id :tg/node-1 :children [:tg/node-2]}
             {:db/id :tg/node-2 :children [:tg/node-3]}
             {:db/id :tg/node-3 :children [:tg/node-4]}
             {:db/id :tg/node-4}])

(d/q '[:find ?parents
       :in $
       :where [?parents ?a+ :tg/node-4] [?parents :children]]
     (d/db conn))

;; => ([:tg/node-root] [:tg/node-1] [:tg/node-2] [:tg/node-3])


(d/q '[:find ?parents
       :in $ ?child
       :where [?parents ?a+ ?child] [?parents :children]]
     (d/db conn) :tg/node-4)

;; => ([:tg/node-root] [:tg/node-2] [:tg/node-1] [:tg/node-3])

The order of results is not specified. Despite being returned as a seq, it’s defined as set operations, so order should not matter. (I guess this can be addressed with an :order-by clause, like SQL has). The reason the order is different is because the query optimizer sees the :where clause differently, since it doesn’t know what ?child is being bound to

That could be addressed by taking bindings to scalars (like this), and rewriting the query before the planner is executed

Hm, okay, I guess I was misled by the first couple of example results being ordered in the https://github.com/threatgrid/asami/wiki/6.-Querying#transitive-attributes. So, just to confirm I'm not misunderstanding, there is no way to obtain the ordered path using transitive attributes (in a single query)?

There should be… Actually, I was really thinking of it as a standard pattern query, and not transitive. Looking at it, I’m surprised that there is a difference in the result. One thing I’ll note though is that even with ?child bound, you’re asking for an unbound attribute, which is a bit of a wildcard. This causes a breadth-first search across the database, which is kind of expensive! It’s always better to bind the attribute to a value or set of values, if that’s feasible

I’m wondering if that’s what sets it off?

How does it look if ?a+ gets replaced with :children+ ?

(I realize that this isn’t the same thing. I’m just wondering that’s the reason for the lack of order)

That won't work here because :children has an array as a value.

So, we have the chain

:tg/node-3     :children    :tg/node-ARRAY
:tg/node-ARRAY :tg/contains :tg/node-4

About binding, not sure how I would re-write it. The idea is to have a function which returns the ordered path back to the root from given a node.

Hmm, OK. I would definitely want it to be evaluating the [?parents :children] first with :planner :user. The reason is because without it, it could find:

:tg/node-3     :children    :tg/node-ARRAY
:tg/node-ARRAY :tg/contains :tg/node-4
:tg/node-ARRAY :tg/first    :tg/node-4

:tg/node-3       :children    :tg/node-ARRAY
:tg/node-ARRAY   :tg/first    :tg/node-4
:tg/node-ARRAY   :tg/rest     :tg/node-ARRAY-2
:tg/node-ARRAY   :tg/contains :tg/node-4
:tg/node-ARRAY   :tg/contains :tg/node-5
:tg/node-ARRAY-2 :tg/first    :tg/node-5