Hi Blake,
Entities don’t have a type, per se, in Datomic, but what attributes an entity has can be thought of as its type. For example, if there is a:person/id attribute, having that attribute could mean an entity is of type person. If an entity with a :person/id also has the attribute :customer/orders you know it is a person and an active customer.
A query for all persons in the DB might look like:
(d/q [:find ?person
:in $
:where [?person :person/id]]
db)
which returns all entities with the attribute :person/id.