Follow-up: lift in-transaction! to DB; make transactions exclusive.

src/datomish/db.cljc

@@ -67,6 +67,12 @@
     [db]
     "TODO: document this interface.")
 
+  (in-transaction!
+    [db chan-fn]
+    "Evaluate the given pair-chan `chan-fn` in an exclusive transaction. If it returns non-nil,
+    commit the transaction; otherwise, rollback the transaction.  Returns a pair-chan resolving to
+    the pair-chan returned by `chan-fn`.")
+
   (<eavt
     [db pattern]
     "Search for datoms using the EAVT index.")
@@ -132,6 +138,10 @@
     [db]
     (inc (:current-tx db)))
 
+  (in-transaction! [db chan-fn]
+    (s/in-transaction!
+      (:sqlite-connection db) chan-fn))
+
   ;; TODO: use q for searching?  Have q use this for searching for a single pattern?
   (<eavt [db pattern]
     (let [[e a v] pattern
@@ -1077,8 +1087,8 @@
   [conn tx-data]
   {:pre [(conn? conn)]}
   (let [db (db conn)] ;; TODO: be careful with swapping atoms.
-    (s/in-transaction!
+    (in-transaction!
-      (:sqlite-connection db)
+      db
       #(go-pair
          (let [report (<? (<with db tx-data))]
            (reset! (:current-db conn) (:db-after report))

src/datomish/sqlite.cljc

@@ -76,7 +76,7 @@
 (defn in-transaction! [db chan-fn]
   (go
     (try
-      (<? (execute! db ["BEGIN TRANSACTION"]))
+      (<? (execute! db ["BEGIN EXCLUSIVE TRANSACTION"]))
       (let [[v e] (<! (chan-fn))]
         (if v
           (do