Fetch everything during a read in one go (#20)

* read data in one shot

* fix formatting

Author: alekcz

src/konserve_jdbc/core.clj

@@ -151,12 +151,19 @@
                   :size nil})
       (extract-bytes res db-type))))
 
+(defn read-all [db-type connection table id]
+  (let [res (-> (jdbc/execute! connection
+                               [(str "SELECT id, header, meta, val FROM " table " WHERE id = '" id "';")]
+                               {:builder-fn rs/as-unqualified-lower-maps})
+                first)]
+    (into {} (for [[k v] res] [k (if (= k :id) v (extract-bytes v db-type))]))))
+
 (extend-protocol PBackingLock
   Boolean
   (-release [_ env]
     (if (:sync? env) nil (go-try- nil))))
 
-(defrecord JDBCRow [table key data]
+(defrecord JDBCRow [table key data cache]
   PBackingBlob
   (-sync [_ env]
     (async+sync (:sync? env) *default-sync-translation*
@@ -172,17 +179,20 @@
     (if (:sync? env) true (go-try- true)))                       ;; May not return nil, otherwise eternal retries
   (-read-header [_ env]
     (async+sync (:sync? env) *default-sync-translation*
-                (go-try- (read-field (:dbtype (:db-spec table)) (:connection table) (:table table) key :header))))
+                (go-try-
+                 (when-not @cache
+                   (reset! cache (read-all (:dbtype (:db-spec table)) (:connection table) (:table table) key)))
+                 (-> @cache :header))))
   (-read-meta [_ _meta-size env]
     (async+sync (:sync? env) *default-sync-translation*
-                (go-try- (read-field (:dbtype (:db-spec table)) (:connection table) (:table table) key :meta))))
+                (go-try- (-> @cache :meta))))
   (-read-value [_ _meta-size env]
     (async+sync (:sync? env) *default-sync-translation*
-                (go-try- (read-field (:dbtype (:db-spec table)) (:connection table) (:table table) key :val))))
+                (go-try- (-> @cache :val))))
   (-read-binary [_ _meta-size locked-cb env]
     (async+sync (:sync? env) *default-sync-translation*
-                (go-try- (read-field (:dbtype (:db-spec table)) (:connection table) (:table table) key :val
-                                     :binary? true :locked-cb locked-cb))))
+                (go-try- (locked-cb {:input-stream (when (-> @cache :val) (ByteArrayInputStream. (-> @cache :val)))
+                                     :size nil}))))
   (-write-header [_ header env]
     (async+sync (:sync? env) *default-sync-translation*
                 (go-try- (swap! data assoc :header header))))
@@ -200,7 +210,7 @@
   PBackingStore
   (-create-blob [this store-key env]
     (async+sync (:sync? env) *default-sync-translation*
-                (go-try- (JDBCRow. this store-key (atom {})))))
+                (go-try- (JDBCRow. this store-key (atom {}) (atom nil)))))
   (-delete-blob [_ store-key env]
     (async+sync (:sync? env) *default-sync-translation*
                 (go-try- (jdbc/execute! connection