when you call (into {} some-entity-map), why isn’t :db/id part of the resulting map? just wondering if there’s a good reason, before I make an entity->map helper that does copy the :db/id

@wei probably because :db/id is not part of the keySet(): http://docs.datomic.com/javadoc/datomic/Entity.html#keySet--

What do you use to store timestamp with timezone?

java.util.Date does not contain timezone info, so if you are using :db.type/instant you will need to store the timezone in a different datom

I'm looking into set intersection query ("give me all products with features a, b AND c")

Here's what I could come up with: https://gist.github.com/pesterhazy/1e0ce9f18035b1693ee9e55241b23be6

Is there a more elegant way than programmatically generating queries?

@pesterhazy entity ref collections are sets; i’d try filtering over all entities with :cat.product/features and doing set intersections with clojure.set/intersection on the set of entities for the slugs

something like this

(let [slugs    ...
      db       ...
      ent-fn   #(d/entity db %)
      features (into []
                     (comp (map (fn [slug]
                                  [:cat.feature/slug slug]))
                           (map ent-fn))
                     slugs)]
  (into []
        (comp (map ent-fn)
              (filter #(seq (clojure.set/intersection (:cat.product/features %) features))))
        (d/datoms db :aevt :cat.product/features)))

you can make dynamic datalog queries, and it should cache its own pre-processing on the result of your make-intersection-q for each of the n values for future use. you might instead want to produce a value for http://docs.datomic.com/clojure/#datomic.api/query, which puts args and datalog syntax into a single structure

@pesterhazy perhaps build up a rule for the AND-ing of the slugs?

(let [rule [(into '[(slug-and [?e])] (map #(vector '?e :cat.feature/slug %) feature-slugs))]]
  (d/q
   '{:find [?e]
   :in [$ %]
   :where [(slug-and ?e)]}
   db
   rule))

ah dynamically generating a rule, interesting!

@robert-stuttaford wouldn't your solution be slower, as it has to generate the feature set for each product?

> you might instead want to produce a value for http://docs.datomic.com/clojure/#datomic.api/query, which puts args and datalog syntax into a single structure

what do you mean by that?

ah there's a difference between q and query

very interesting stuff

possibly, @pesterhazy - i suppose it would!

@pesterhazy dynamic conjunction can be achieved using double negation and dynamic disjunction in Datalog

i like @thegeez ‘s idea

@val_waeselynck is there a code sample that illustrates your idea?

De Morgan's law?

@robert-stuttaford working on it 🙂 not sure it's possible in this case because of the constraint that not-join must operate on one data source

@pesterhazy yeah essentially

my autodidactism bites again. never did CS -pout-

neat!

but i don't think this one will work out of the box

because of the fact that not-join works only on one data source

I'm in the same boat Robert

the following may work

not sure about the performance though 🙂

Nice!!

This is not the first time I see something like this come up - should probably be part of some best practices / tips and tricks section of the Datomic docs

If this does not work-out performance-wise, then yeah, probably either generate a query or rule, or call a function in-query which performs the EAVT traversal, or a combination of both 🙂

mind if I write a blog post summarising your approach?

@pesterhazy no problem whatsoever 🙂

has anyone written a library for using pull syntax on local data structures?

@uwo Sort of https://github.com/stuartsierra/mapgraph

@stuartsierra thanks!

thanks, makes sense. wondering about the justification for not including it.

@wei, the db/id is not really an attribute of the entity

although it is shown when you print the entity

I suppose you could (-> entity pr-str read-string)? 🙂