Queries and pull#

Datalog#

Queries are data and take explicit inputs:

(d/q '[:find ?name
       :in $ ?active
       :where
       [?e :person/active ?active]
       [?e :person/name ?name]]
     db
     true)

Supported query features include:

relation, collection, tuple, and scalar :find
database and value inputs
data, predicate, and function clauses
not, not-join, or, and or-join
aggregates
rules, including recursive rules
pull expressions in :find
:with and return maps

The EDN frontend accepts vector and map query forms. Native APIs also provide prepared queries and typed result access.

Pull#

Pull returns selected attributes for one or more entities:

(d/pull db
  [:person/name
   {:person/friends [:person/name]}]
  person-id)

Supported patterns include:

attribute keywords
wildcard *
nested joins
reverse attributes
recursion limits
:as, :default, :limit, and :xform
lookup refs

Entity reads#

Entity views provide lazy attribute lookup against one immutable database value. Reference attributes can be followed without reading from the live connection.

Use pull when the result shape is known. Use entity views for incremental navigation.

Index reads#

Use datoms, seek-datoms, rseek-datoms, or index-range when index order is part of the operation. See Data model.

Exact function names and result types vary by package. See the package repository for the host language.