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

/*
 * 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
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package de.uapcore.lightpit.dao;

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Types;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.function.Function;

public abstract class AbstractDao<T> implements GenericDao<T> {

    private final PreparedStatement listQuery;

    protected AbstractDao(PreparedStatement listQuery) {
        this.listQuery = listQuery;
    }

    public final T mapColumns(ResultSet result) throws SQLException {
        return mapColumns(result, "");
    }

    public abstract T mapColumns(ResultSet result, String qualifier) throws SQLException;

    /**
     * Qualifies a column label if an qualifier is specified.
     *
     * @param qualifier an optional qualifier
     * @param label     the column label
     * @return the label, qualified if necessary
     */
    protected final String qual(String qualifier, String label) {
        if (qualifier == null || qualifier.isBlank()) {
            return label;
        } else {
            return qualifier + "." + label;
        }
    }

    protected final void setStringOrNull(PreparedStatement stmt, int index, String str) throws SQLException {
        if (str == null || str.isBlank()) {
            stmt.setNull(index, Types.VARCHAR);
        } else {
            stmt.setString(index, str);
        }
    }

    protected final <T> void setForeignKeyOrNull(PreparedStatement stmt, int index, T instance, Function<T, Integer> keyGetter) throws SQLException {
        Integer key = Optional.ofNullable(instance).map(keyGetter).orElse(null);
        if (key == null) {
            stmt.setNull(index, Types.INTEGER);
        } else {
            stmt.setInt(index, key);
        }
    }

    @Override
    public List<T> list() throws SQLException {
        List<T> list = new ArrayList<>();
        try (ResultSet result = listQuery.executeQuery()) {
            while (result.next()) {
                list.add(mapColumns(result));
            }
        }
        return list;
    }
}