Add fetchOne(RecordMapper) shortcut method to ResultQuery and implement it in implementing classes

jOOQ/src/main/java/org/jooq/ResultQuery.java

@@ -457,6 +457,17 @@ public interface ResultQuery<R extends Record> extends Query, Iterable<R> {
      */
     R fetchOne() throws DataAccessException, InvalidResultException;
 
+    /**
+     * Execute the query and return at most one resulting value into a
+     * custom mapper callback.
+     *
+     * @return The custom mapped record or <code>null</code> if the query returned no
+     *         records.
+     * @throws DataAccessException if something went wrong executing the query
+     * @throws InvalidResultException if the query returned more than one record
+     */
+    <E> E fetchOne(RecordMapper<? super R, E> mapper) throws DataAccessException, InvalidResultException;
+
     /**
      * Execute the query and return at most one resulting record as a name/value
      * map.

jOOQ/src/main/java/org/jooq/impl/AbstractResultQuery.java

@@ -440,6 +440,12 @@ abstract class AbstractResultQuery<R extends Record> extends AbstractQuery imple
         return Utils.fetchOne(fetchLazy());
     }
 
+    @Override
+    public final <E> E fetchOne(RecordMapper<? super R, E> mapper) {
+        R record = fetchOne();
+        return record == null ? null : mapper.map(record);
+    }
+
     @Override
     public final Map<String, Object> fetchOneMap() {
         R record = fetchOne();

jOOQ/src/main/java/org/jooq/impl/SelectImpl.java

@@ -2436,6 +2436,11 @@ class SelectImpl<R extends Record, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11,
         return getDelegate().fetchOne();
     }
 
+    @Override
+    public final <E> E fetchOne(RecordMapper<? super R, E> mapper) {
+        return getDelegate().fetchOne(mapper);
+    }
+
     @Override
     public final Map<String, Object> fetchOneMap() {
         return getDelegate().fetchOneMap();