src/main/java/de/uapcore/lightpit/dao/ChildEntityDao.java

/*
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 *
 * Copyright 2018 Mike Becker. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
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 *      notice, this list of conditions and the following disclaimer in the
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 *
 * 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
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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);
        }
    }
}