WordPress│記事中のカスタムフィールド値をcsvでエクスポートする方法│プラグイン不要

<?php
function waza_cf_csv_cell($value) {
    $value = (string) $value;
    return preg_match('/^[\x00-\x20]*[=+@-]/', $value) ? "'" . $value : $value;
}
function waza_cf_csv_rows($post) {
    $rows = [];
    if (!$post instanceof WP_Post) return $rows;
    foreach (get_post_meta($post->ID) as $key => $unused) {
        $key = (string) $key;
        if ($key === '' || $key[0] === '_') continue;
        $json = wp_json_encode(get_post_meta($post->ID, $key, false), JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
        if ($json === false) continue;
        $rows[] = array_map('waza_cf_csv_cell', [$post->ID, $post->post_title, $post->post_status, $key, $json]);
    }
    return $rows;
}
function waza_cf_csv_batch($type, $after, $max = 0) {
    global $wpdb;
    if (!in_array($type, ['post','page'], true) || $after < 0 || $max < 0) return new WP_Error('invalid', '対象またはIDが不正です');
    if (!$max) $max = (int) $wpdb->get_var($wpdb->prepare("SELECT MAX(ID) FROM {$wpdb->posts} WHERE post_type=%s", $type));
    $ids = $wpdb->get_col($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE post_type=%s AND post_status IN ('publish','draft','pending','private') AND ID>%d AND ID<=%d ORDER BY ID ASC LIMIT 250", $type, $after, $max));
    if ($wpdb->last_error) return new WP_Error('query', '投稿IDを取得できませんでした');
    return ['ids'=>array_map('intval', $ids), 'max'=>$max, 'next'=>$ids ? (int) end($ids) : $after];
}
add_action('admin_menu', function () {
    add_management_page('CF CSV出力', 'CF CSV出力', 'manage_options', 'waza-cf-csv', function () {
        if (!current_user_can('manage_options')) return;
        echo '<div class="wrap"><h1>CF CSV出力</h1><p>初回は両方のIDを0にします。続きはファイル名のnextとmaxを指定します。</p>';
        echo '<form method="post" action="' . esc_url(admin_url('admin-post.php')) . '">';
        echo '<input type="hidden" name="action" value="waza_cf_csv">';
        wp_nonce_field('waza_cf_csv');
        echo '<p><label>対象 <select name="post_type"><option value="post">投稿</option><option value="page">固定ページ</option></select></label></p>';
        echo '<p><label>前回のnext ID <input type="number" min="0" name="after" value="0" required></label></p>';
        echo '<p><label>初回のmax ID <input type="number" min="0" name="max" value="0" required></label></p>';
        submit_button('CSVをダウンロード');
        echo '</form></div>';
    });
});
add_action('admin_post_waza_cf_csv', function () {
    if (!current_user_can('manage_options')) wp_die('権限がありません');
    check_admin_referer('waza_cf_csv');
    $type = isset($_POST['post_type']) && is_string($_POST['post_type']) ? wp_unslash($_POST['post_type']) : '';
    $parse = function ($key) { return isset($_POST[$key]) && is_string($_POST[$key]) ? filter_var($_POST[$key], FILTER_VALIDATE_INT, ['options'=>['min_range'=>0]]) : false; };
    $after = $parse('after'); $max = $parse('max');
    if ($after === false || $max === false || ($after > 0 && $max === 0)) wp_die('続きの出力ではnextとmaxの両方を指定してください');
    $batch = waza_cf_csv_batch($type, $after, $max);
    if (is_wp_error($batch)) wp_die(esc_html($batch->get_error_message()));
    if (!$batch['ids']) wp_die('この範囲に残りの対象記事はありません');
    if (headers_sent()) wp_die('出力が始まっているためCSVを作成できません');
    nocache_headers();
    header('Content-Type: text/csv; charset=UTF-8');
    header('Content-Disposition: attachment; filename="custom-fields-' . $type . '-after-' . $after . '-next-' . $batch['next'] . '-max-' . $batch['max'] . '.csv"');
    $out = fopen('php://output', 'w');
    if (!$out) wp_die('CSVを出力できません');
    fwrite($out, "\xEF\xBB\xBF");
    fputcsv($out, ['post_id','post_title','post_status','meta_key','values_json'], ',', '"', '');
    foreach ($batch['ids'] as $id) {
        if (!current_user_can('edit_post', $id)) continue;
        foreach (waza_cf_csv_rows(get_post($id)) as $row) fputcsv($out, $row, ',', '"', '');
    }
    fclose($out);
    exit;
});