[SOLVED] Datomic query: find all entities with some value

Datomic query: find all entities with some value

With this query:

{:find  [?e]
         :where [[?e :db/valueType :db.type/string]]}

I can find all entities with property named :db/valueType and value of :db.type/string. In my case with some data in the database it returns ten IDs.

How would I search for all entities with value of :db.type/string, regardless of the property name? For example this query:

{:find  [?e]
         :where [[?e _ :db.type/string]]}

returns an empty set. As far as I can understand Datomic's Datalog, _ should work as a wildcard, matching anything, so the second query should at least return the same number of results as the first one, and maybe even more than that.

Thanks...

Solution

For this example, the logical structure of the query is essentially correct, but the attribute ident keyword is not being resolved to its entity id. Note that this is a special case that occurs when you query with attributes as inputs - a scenario in which the query engine is not guaranteed to perform this conversion. See the Datomic docs on query (http://docs.datomic.com/query.html) for "Attributes as Query Inputs."

A way to restructure this query is as:

    (let [db (d/db conn)] 
            (d/q '[:find ?e 
                   :in $ ?id 
                   :where [?e _ ?id]] 
             db (d/entid db :db.type/string)))

In this case, we resolve the keyword :db.type/string to its entity id manually in the input to the parameterized query.