fix #237 by adding :init-fn option

CHANGELOG.md

@@ -4,6 +4,7 @@ Only accretive/fixative changes will be made from now on.
 
 * 1.3.next in progress
   * Address [#245](https://github.com/seancorfield/next-jdbc/issues/245) by not `locking` the `Connection` when `*nested-tx*` is bound to `:ignore` -- improving `clojure.java.jdbc` compatibility.
+  * Address [#237](https://github.com/seancorfield/next-jdbc/issues/237) by adding an `:init-fn` option to the `db-spec` argument for `next.jdbc.connection/component`.
 
 * 1.3.862 -- 2023-03-13
   * Fix [#243](https://github.com/seancorfield/next-jdbc/issues/243) by ensuring URI properties become keywords.

doc/getting-started.md

@@ -568,6 +568,12 @@ If you are using [Component](https://github.com/stuartsierra/component), a conne
         (component/stop ds)))))
 ```
 
+If you have want to either modify the connection pooled datasource after it is
+created, or want to perform some database initialization, you can pass a
+function as `:init-fn` in the `db-spec` hash map. The `component` function
+will arrange for that initialization function to be invoked on the newly-created
+datasource whenever `start` is called on the Component returned.
+
 ## Working with Additional Data Types
 
 By default, `next.jdbc` relies on the JDBC driver to handle all data type conversions when reading from a result set (to produce Clojure values from SQL values) or setting parameters (to produce SQL values from Clojure values). Sometimes that means that you will get back a database-specific Java object that would need to be manually converted to a Clojure data structure, or that certain database column types require you to manually construct the appropriate database-specific Java object to pass into a SQL operation. You can usually automate those conversions using either the [`ReadableColumn` protocol](/doc/result-set-builders.md#readablecolumn) (for converting database-specific types to Clojure values) or the [`SettableParameter` protocol](/doc/prepared-statements.md#prepared-statement-parameters) (for converting Clojure values to database-specific types).

src/next/jdbc/connection.clj

@@ -1,4 +1,4 @@
-;; copyright (c) 2018-2021 Sean Corfield, all rights reserved
+;; copyright (c) 2018-2023 Sean Corfield, all rights reserved
 
 (ns next.jdbc.connection
   "Standard implementations of `get-datasource` and `get-connection`.
@@ -288,6 +288,11 @@
   called on it to shutdown the datasource (and return a new startable
   entity).
 
+  If `db-spec` contains `:init-fn`, that is assumed to be a function
+  that should be called on the newly-created datasource. This allows for
+  modification of (mutable) connection pooled datasource and/or some sort
+  of database initialization/setup to be called automatically.
+
   By default, the datasource is shutdown by calling `.close` on it.
   If the datasource class implements `java.io.Closeable` then a direct,
   type-hinted call to `.close` will be used, with no reflection,
@@ -305,7 +310,9 @@
    (with-meta {}
      {'com.stuartsierra.component/start
       (fn [_]
-        (let [pool (->pool clazz db-spec)]
+        (let [init-fn (:init-fn db-spec)
+              pool    (->pool clazz (dissoc db-spec :init-fn))]
+          (when init-fn (init-fn pool))
           (with-meta (fn ^DataSource [] pool)
             {'com.stuartsierra.component/stop
              (fn [_]