Cannot refer to a unique ref with a map

Use case:

• I want to be able to describe 1-to-1 relationships in my schema.
• My solution is to create unique refs in my schema.

Did:

• Added an attribute :foo to my schema with both :db/valueType :db.type/ref and :db/unique db.unique/identity.
• Transacted an entity associating :foo to a map (ref)

Expected:

• :foo to associated with the reference, which is unique in the db.
• Refs can be unique and used in this way in Datomic.

Happened:

• Error: #error {:message "Expected number or lookup ref for entity id, got {:db/id 1}", :data {:error :entity-id/syntax, :entity-id {:db/id 1}}}

Code to repro:

(require '[datascript.core :as d])

(def conn (d/create-conn {:foo {:db/valueType :db.type/ref 
                                :db/unique    :db.unique/identity}}))
(d/transact conn [{:db/id 1}{:foo 1}]) ;; OK, when referencing with a number

(def conn (d/create-conn {:foo {:db/valueType :db.type/ref 
                                :db/unique    :db.unique/identity}}))
(d/transact conn [{:db/id 1}{:foo {:db/id 1}}]) ;; throws, when using a map

Run the supplied Clojure reproduction using d/transact first, then trace how transaction handling processes ref entity IDs and unique lookup refs. Done means the second transaction accepts {:db/id 1} as a reference and the reproduction no longer throws the reported :entity-id/syntax error.