clarify that @Generated does not always require a separate select statement

Signed-off-by: Gavin King <gavin@hibernate.org>

hibernate-core/src/main/java/org/hibernate/annotations/Generated.java

@@ -17,8 +17,21 @@ import static org.hibernate.generator.EventType.INSERT;
 
 /**
  * Specifies that the value of the annotated property is generated by the
- * database. The generated value will be automatically retrieved using a
+ * database. The generated value is automatically retrieved after it is
- * SQL {@code select} after it is generated.
+ * generated.
+ * <p>
+ * Retrieval of the generated value might require an additional SQL
+ * {@code select} statement, but this not necessary if:
+ * <ul>
+ * <li>
+ * the SQL dialect of the database
+ * {@linkplain org.hibernate.dialect.Dialect#supportsInsertReturning
+ * supports} {@code returning} or {@code select from final table}, or
+ * <li>
+ * the JDBC driver
+ * {@linkplain org.hibernate.dialect.Dialect#supportsInsertReturningGeneratedKeys
+ * provides} a similar capability via {@code getGeneratedKeys()}.
+ * </ul>
  * <p>
  * {@code @Generated} relieves the program of the need to explicitly call
  * {@link org.hibernate.Session#refresh(Object) refresh()} to synchronize

hibernate-core/src/main/java/org/hibernate/dialect/Dialect.java

@@ -4242,8 +4242,8 @@ public abstract class Dialect implements ConversionContext, TypeContributor, Fun
 	 * <p>
 	 * Support for identity columns is insufficient here, we require something like:
 	 * <ol>
-	 * <li>{@code insert ... returning ...}
+	 * <li>{@code insert ... returning ...}, or
-	 * <li>{@code select from final table (insert ... )}
+	 * <li>{@code select from final table (insert ... )}.
 	 * </ol>
 	 *
 	 * @return {@code true} if {@link org.hibernate.id.insert.InsertReturningDelegate}