added comment about subclassing DataTable

src/serversdk/databasetable.h

@@ -129,6 +129,31 @@ public:
      * @brief Convert QVariant type to SQL type
      * @param QVariant type ( QString, int, QDateTime )
      * @return text form of database type ( INTEGER, TEXT )
+     *
+     * # Sublassing
+     *
+     * When it is neccessary to use different type it is possible to subclass and override this method.
+     *
+     * @code
+        class BackendTable : public serversdk::DatabaseTable
+        {
+          QString textPostgresType(QVariant::Type type) const override;
+        }
+
+        BackendTable::textPostgresType(QVariant::Type type) const override
+        {
+            // For case when saving date time as ms since epoch
+            if (type == QVariant::DateTime) {
+                return QStringLiteral("INTEGER");
+            }
+            return DatabaseTable::textPostgresType(type);
+        }
+
+     * @endcode
+     *
+     *
+     *
+     *
      */
     virtual QString textPostgresType(QVariant::Type type) const;