Avoid copying plain map when converting to instance (#165)

* Avoid copying plain map when converting to instance

* Try again

* Missing case

src/toucan2/instance.clj

@@ -16,7 +16,8 @@
    [potemkin :as p]
    [pretty.core :as pretty]
    [toucan2.protocols :as protocols]
-   [toucan2.realize :as realize]))
+   [toucan2.realize :as realize]
+   [toucan2.util :as u]))
 
 (set! *warn-on-reflection* true)
 
@@ -267,9 +268,13 @@
      ;; (instance? m)
      ;; (protocols/with-model m model)
 
-     :else
+     ;; Strip any customizations, e.g. a different underlying empty map or key transform.
+     (u/custom-map? m)
      (let [m* (into {} m)]
-       (->Instance model m* m* (meta m)))))
+       (->Instance model m* m* (meta m)))
+
+     :else
+     (->Instance model m m (meta m))))
 
   (^toucan2.instance.Instance [model k v & more]
    (let [m (into {} (partition-all 2) (list* k v more))]

src/toucan2/jdbc/row.clj

@@ -15,7 +15,8 @@
    [toucan2.instance :as instance]
    [toucan2.log :as log]
    [toucan2.protocols :as protocols]
-   [toucan2.realize :as realize])
+   [toucan2.realize :as realize]
+   [toucan2.util :as u])
   (:import
    (java.sql ResultSet)))
 
@@ -280,6 +281,9 @@
   (realize [_this]
     @realized-row)
 
+  u/IsCustomMap
+  (custom-map? [_] true)
+
   (toString [this]
     (str/join \space (map str (print-representation-parts this)))))
 

src/toucan2/util.clj

@@ -5,7 +5,10 @@
    [clojure.walk :as walk]
    [methodical.util.dispatch :as m.dispatch]
    [pretty.core :as pretty]
-   [toucan2.protocols :as protocols]))
+   [toucan2.protocols :as protocols])
+  (:import
+   (clojure.lang IPersistentMap)
+   (potemkin.collections PotemkinMap)))
 
 ;;; TODO -- there is a lot of repeated code in here to make sure we don't accidentally realize and print `IReduceInit`,
 ;;; and at least 3 places we turn an `eduction` into the same pretty form. Maybe we should try to consolidate some of
@@ -110,3 +113,14 @@
     (keyword (csk/->kebab-case (namespace x))
              (csk/->kebab-case (name x)))
     (csk/->kebab-case x)))
+
+(defprotocol IsCustomMap
+  "Is this a map a transient row, or created using p/def-map-type? This includes Instances."
+  (custom-map? [m]))
+
+(extend-protocol IsCustomMap
+  IPersistentMap
+  (custom-map? [_] false)
+
+  PotemkinMap
+  (custom-map? [_] true))