Can't query entity using :db/id attribute about datascript HOT 2 CLOSED

@nahuel,

:db/id is not a real attribute. It is used to create “map” forms of an entity at insert stage. When you write

(d/transact! db [{:db/id -1 :name "Mazinger"}]

it means, essentially, this: take all key-value pairs from this map, convert them to [:db/add eid attr value] form where attr=key from map, value=value from map, and eid (entity id) is a special key :db/id from map. It’s just a convention. Results from entity calls support this convention too, as they have to represent datoms as maps.

But inside DataScript everything is stored as flat datoms of form [e a v], no maps. If your entity has 10 attributes, there’ll be 10 distinct datoms. Maps are just a convenient view of these internals.

Queries are written in pattern-match style over actual flat datoms, so you cannot use :db/id as it is not an actual datom attribute. When matching over entity id, just use first position, not last one:

(d/q `[:find ?name
       :where [~new-id :name ?name]] @db)

BTW it’s not recommended to use actual values inside query. For parametrized queries, use addtional :in agruments:

(d/q '[:find ?name
       :in $ ?e
       :where [?e :name ?name]] @db new-id)

from datascript.

Now it's crystal clear, many thanks for the detailed response!

from datascript.