Clojurians Log v2

@jaret @marshall what does it mean if i can see a datom in a d/db but not in a d/history of that same db?

@robert-stuttaford any chance the attribute has :db/noHistory set to true?

@robert-stuttaford second thought, you’re getting the history db from the db you see the datom in? If so, that sounds like something we would want to investigate. Would you be able to give us a small repro or better yet, a backup that shows this behavior?

that's right - db and (d/history db)

@jaret it's in our prod db, which has all our PII in it, started circa 2012 🙂

perhaps we could arrange a zoom and i could show you via screen share, and then we can see about next steps from there?

Hey there, we are using datomic and are currently diagnosing a performance issue related to a recursive rule. We have a tree structure in datomic, that for each node, links a parent (or not), so a schema like this:

(def schema
  [;; Additional tree attributes omitted
   {:db/ident       :node/parent
    :db/valueType   :db.type/ref
    :db/cardinality :db.cardinality/one}])

(def descendants-of?
  '[[(descendants-of? ?root ?node)
     [?node :node/parent ?root]]
    [(descendants-of? ?root ?node)
     [?node :node/parent ?intermediate]
     (descendants-of? ?root ?intermediate)]])

(d/q '[:find ?node
             :in $ ?e %
             :where
             (descendants-of? ?e ?node)]
           (d/db (conn))
           root-eid
           descendants-of?])

(d/q '[:find ?node
             :in $ ?name %
             :where
             ;; assuming that `?name` only exists in one tree
             [?e :node/name ?name]
             (descendants-of? ?e ?node)]
           (d/db (conn))
           “name”
           descendants-of?])

Using :as with :db/id does not appear to have any effect. Is this expected?

(d/q
    '[:find (pull ?e [(:db/id :as "foo")])
      :where
      [?e :db/ident :db/cardinality]]
    (d/db conn))
=> [[#:db{:id 41, :ident :db/cardinality}]]

Other db/* attrs work:

(d/pull (d/db conn)
          '[(:db/id :as "foo")
            (:db/ident :as "ident")]
          :db/cardinality)
=> {:db/id 41, :db/ident :db/cardinality, "ident" :db/cardinality}

This one is strange since :db/ident is included twice.

:db/doc is not included twice.

(d/pull (d/db conn)
          '[(:db/id :as "foo")
            (:db/ident :as "ident")
            (:db/doc :as "doc")]
          :db/cardinality)
=>
{:db/id 41,
 :db/ident :db/cardinality,
 "ident" :db/cardinality,
 "doc" "Property of an attribute. Two possible values: :db.cardinality/one for single-valued attributes, and :db.cardinality/many for many-valued attributes. Defaults to :db.cardinality/one."}

@kenny :db/id isn't an attribute. where is no Datom[e :db/id v]. It's a "special thing" that d/pull assoc into it's response.

So? I don't think pull requires the selection to be attributes. From the doc "Pull is a declarative way to make hierarchical (and possibly nested) selections of information about entities."

Even if that was a requirement, I don't think it makes sense for it to behave differently than everything else.

I agree that it's a bug

Why not:

'[[(descendants-of? ?root ?node)
   [?node :node/parent ?root]]
  [(descendants-of? ?root ?node)
   [?intermediate :node/parent ?root]
   (descendants-of? ?intermediate ?node)]]

The second implementation of decendents-of? necessarily scans all :node/parent if ?node is unbound

if you know ?root is bound, you can start from that

in fact, datomic has a syntax for ensuring a rule input var is bound:

'[[(descendants-of? [?root] ?node)
   [?node :node/parent ?root]]
  [(descendants-of? [?root] ?node)
   [?intermediate :node/parent ?root]
   (descendants-of? ?intermediate ?node)]]

Ah let me take a look, I may have simplified the example a bit too much when lifting it from our codebase

Opened a support ticket for this https://support.cognitect.com/hc/en-us/requests/2797

Oh you are on to something! Thank you so much