diff -r 4f912cd42876 -r 86b5d8a1662f src/main/java/de/uapcore/lightpit/dao/ChildEntityDao.java
--- a/src/main/java/de/uapcore/lightpit/dao/ChildEntityDao.java	Fri Nov 06 10:50:32 2020 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,116 +0,0 @@
-/*
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
- *
- * Copyright 2018 Mike Becker. All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions are met:
- *
- *   1. Redistributions of source code must retain the above copyright
- *      notice, this list of conditions and the following disclaimer.
- *
- *   2. Redistributions in binary form must reproduce the above copyright
- *      notice, this list of conditions and the following disclaimer in the
- *      documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
- * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
- * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
- * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
- * POSSIBILITY OF SUCH DAMAGE.
- *
- */
-package de.uapcore.lightpit.dao;
-
-import java.sql.SQLException;
-import java.util.List;
-
-public interface ChildEntityDao<T, P> {
-
-    /**
-     * Lists all entities being a child of the specified parent.
-     * @param parent the parent
-     * @return the list of child instances
-     * @throws SQLException on any kind of SQL errors
-     */
-    List<T> list(P parent) throws SQLException;
-
-    /**
-     * Finds an entity by its integer ID.
-     * It is not guaranteed that referenced entities are automatically joined.
-     *
-     * @param id the id
-     * @return the enity or null if there is no such entity
-     * @throws SQLException on any kind of SQL errors
-     */
-    T find(int id) throws SQLException;
-
-    /**
-     * Inserts an instance into database.
-     * It is not guaranteed that generated fields will be updated in the instance.
-     *
-     * @param instance the instance to insert
-     * @param parent a reference to the parent
-     * @throws SQLException on any kind of SQL errors
-     */
-    void save(T instance, P parent) throws SQLException;
-
-    /**
-     * Updates an instance in the database.
-     *
-     * @param instance the instance to insert
-     * @return true if an instance has been updated, false if no instance with the specified ID was found
-     * @throws SQLException on any kind of SQL errors
-     */
-    boolean update(T instance) throws SQLException;
-
-    /**
-     * Updates an instance in the database changing the parent.
-     * This operation is not supported by default.
-     *
-     * @param instance the instance to insert
-     * @param newParent a reference to the new parent
-     * @return true if an instance has been updated, false if no instance with the specified ID was found
-     * @throws SQLException on any kind of SQL errors
-     * @see #isChangingParentSupported()
-     */
-    default boolean update(T instance, P newParent) throws SQLException {
-        throw new UnsupportedOperationException();
-    }
-
-    /**
-     * Returns true if changing the parent is supported by this DAO.
-     * This method must return true, if {@link #update(Object, Object)} is implemented.
-     * @return true, if changing the parent is supported
-     */
-    default boolean isChangingParentSupported() {
-        return false;
-    }
-
-    /**
-     * Inserts or updates an instance in the database.
-     * Tries an update first and if that fails, performs a save.
-     * If changing a parent is not supported by this DAO,
-     * specifying an alternate parent for an existing instance has no effect.
-     *
-     * @param instance the instance to insert or update
-     * @param parent a reference to the parent
-     * @throws SQLException on any kind of SQL errors
-     * @see #update(Object)
-     * @see #update(Object, Object)
-     * @see #save(Object, Object)
-     */
-    default void saveOrUpdate(T instance, P parent) throws SQLException {
-        if (isChangingParentSupported()) {
-            if (!update(instance, parent)) save(instance, parent);
-        } else {
-            if (!update(instance)) save(instance, parent);
-        }
-    }
-}