src/main/java/de/uapcore/lightpit/dao/Functions.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
 * POSSIBILITY OF SUCH DAMAGE.
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 */
package de.uapcore.lightpit.dao;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.function.Function;

/**
 * Some DAO utilities.
 */
public final class Functions {

    public static 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);
        }
    }

    public static void setDateOrNull(PreparedStatement stmt, int index, Date date) throws SQLException {
        if (date == null) {
            stmt.setNull(index, Types.DATE);
        } else {
            stmt.setDate(index, date);
        }
    }

    public static <T> void setForeignKeyOrNull(PreparedStatement stmt, int index, T instance, Function<? super 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);
        }
    }

    @FunctionalInterface
    public interface ResultSetMapper<T> {
        T apply(ResultSet rs) throws SQLException;
    }

    public static <T> List<T> list(PreparedStatement stmt, ResultSetMapper<T> mapper) throws SQLException {
        List<T> results = new ArrayList<>();
        try (var result = stmt.executeQuery()) {
            while (result.next()) {
                final var project = mapper.apply(result);
                results.add(project);
            }
        }
        return results;
    }

    public static <T> T find(PreparedStatement stmt, ResultSetMapper<T> mapper) throws SQLException {
        try (var result = stmt.executeQuery()) {
            if (result.next()) {
                final var ent = mapper.apply(result);
                return ent;
            } else {
                return null;
            }
        }
    }

    private Functions() {

    }
}