Address #70 by adding/documenting CLOB column reader example

CHANGELOG.md

@@ -6,6 +6,7 @@ Only accretive/fixative changes will be made from now on.
 
 The following changes have been committed to the **master** branch since the 1.0.9 release:
 
+* Address #70 by adding `next.jdbc.result-set/clob-column-reader` and `next.jdbc.result-set/clob->string` helper to make it easier to deal with `CLOB` column data.
 * Update `org.clojure/java.data` to `"0.1.4"` (0.1.2 fixes a number of reflection warnings).
 
 ## Stable Builds

doc/result-set-builders.md

@@ -37,6 +37,14 @@ And finally there are adapters for the existing builders that let you override t
 * `as-maps-adapter` -- adapts an existing map builder function with a new column reader,
 * `as-arrays-adapter` -- adapts an existing array builder function with a new column reader.
 
+An example column reader is provided -- `clob-column-reader` -- that still uses `.getObject` but will expand `java.sql.Clob` values into string (using the `clob->string` helper function):
+
+```clojure
+    {:builder-fn (result-set/as-maps-adapter
+                  result-set/as-maps
+                  result-set/clob-column-reader)}
+```
+
 ## RowBuilder Protocol
 
 This protocol defines four functions and is used whenever `next.jdbc` needs to materialize a row from a `ResultSet` as a Clojure data structure:

src/next/jdbc/result_set.clj

@@ -14,9 +14,11 @@
   Also provides the default implemenations for `Executable` and
   the default `datafy`/`nav` behavior for rows from a result set."
   (:require [clojure.core.protocols :as core-p]
+            [clojure.java.io :as io]
             [next.jdbc.prepare :as prepare]
             [next.jdbc.protocols :as p])
-  (:import (java.sql PreparedStatement
+  (:import (java.sql Clob
+                     PreparedStatement
                      ResultSet ResultSetMetaData
                      SQLException)
            (java.util Locale)))
@@ -236,6 +238,21 @@
         (with-row [this mrs row] (with-row mrsb mrs row))
         (rs! [this mrs] (rs! mrsb mrs))))))
 
+(defn clob->string
+  "Given a CLOB column value, read it as a string."
+  [^Clob clob]
+  (with-open [rdr (io/reader (.getCharacterStream clob))]
+    (slurp rdr)))
+
+(defn clob-column-reader
+  "An example column-reader that still uses `.getObject` but expands CLOB
+  columns into strings."
+  [^ResultSet rs ^ResultSetMetaData _ ^Integer i]
+  (when-let [value (.getObject rs i)]
+    (cond-> value
+      (instance? Clob value)
+      (clob->string))))
+
 (defrecord ArrayResultSetBuilder [^ResultSet rs rsmeta cols]
   RowBuilder
   (->row [this] (transient []))

test/next/jdbc/result_set_test.clj

@@ -289,3 +289,30 @@
                             (= "fruit" (-> % val name str/lower-case)))
                       row))
               metadata))))
+
+(deftest clob-reading
+  (when-not (postgres?) ; embedded postgres does not support clob
+    (with-open [con (p/get-connection (ds) {})]
+      (try
+        (p/-execute-one con ["DROP TABLE CLOBBER"] {})
+        (catch Exception _))
+      (p/-execute-one con [(str "
+CREATE TABLE CLOBBER (
+  ID INTEGER,
+  STUFF CLOB
+)")]
+                      {})
+      (p/-execute-one con
+                      [(str "insert into clobber (id, stuff)"
+                            "values (?,?), (?,?)")
+                       1 "This is some long string"
+                       2 "This is another long string"]
+                      {})
+      (is (= "This is some long string"
+             (-> (p/-execute-all con
+                                 ["select * from clobber where id = ?" 1]
+                                 {:builder-fn (rs/as-maps-adapter
+                                               rs/as-unqualified-lower-maps
+                                               rs/clob-column-reader)})
+                 (first)
+                 :stuff))))))

test/next/jdbc_test.clj

@@ -2,8 +2,7 @@
 
 (ns next.jdbc-test
   "Not exactly a test suite -- more a series of examples."
-  (:require [clojure.java.io :as io]
-            [clojure.string :as str]
+  (:require [clojure.string :as str]
             [clojure.test :refer [deftest is testing use-fixtures]]
             [next.jdbc :as jdbc]
             [next.jdbc.connection :as c]
@@ -12,7 +11,7 @@
             [next.jdbc.prepare :as prep]
             [next.jdbc.result-set :as rs]
             [next.jdbc.specs :as specs])
-  (:import (java.sql Clob ResultSet ResultSetMetaData)))
+  (:import (java.sql ResultSet ResultSetMetaData)))
 
 (set! *warn-on-reflection* true)
 
@@ -213,37 +212,3 @@ VALUES ('Pear', 'green', 49, 47)
               (into [] (map pr-str) (jdbc/plan (ds) ["select * from fruit"]))))
   (is (thrown? IllegalArgumentException
                (doall (take 3 (jdbc/plan (ds) ["select * from fruit"]))))))
-
-(defn- clob-reader
-  [^ResultSet rs ^ResultSetMetaData _ ^Integer i]
-  (let [obj (.getObject rs i)]
-    (cond (instance? Clob obj)
-          (with-open [rdr (io/reader (.getCharacterStream ^Clob obj))]
-            (slurp rdr))
-          :default
-          obj)))
-
-(deftest clob-reading
-  (when-not (postgres?)
-    (with-open [con (jdbc/get-connection (ds))]
-      (try
-        (jdbc/execute-one! con ["DROP TABLE CLOBBER"])
-        (catch Exception _))
-      (jdbc/execute-one! con [(str "
-CREATE TABLE CLOBBER (
-  ID INTEGER,
-  STUFF CLOB
-)")])
-      (jdbc/execute-one! con
-                         [(str "insert into clobber (id, stuff)"
-                               "values (?,?), (?,?)")
-                          1 "This is some long string"
-                          2 "This is another long string"])
-      (is (= "This is some long string"
-             (-> (jdbc/execute! con
-                                ["select * from clobber where id = ?" 1]
-                                {:builder-fn (rs/as-maps-adapter
-                                              rs/as-unqualified-lower-maps
-                                              clob-reader)})
-                 (first)
-                 :stuff))))))