How-to: Poll / Survey API

This guide shows how to build a poll and survey system with duplicate vote prevention using NENE2. Pattern demonstrated by the polllog field trial (FT217).

Features

• Create polls with 2–20 options (admin only)
• Public and private polls (private: admin-only access)
• One vote per user per poll (enforced by UNIQUE constraint)
• Live result aggregation with per-option vote counts
• Total vote sum across all options

Schema

CREATE TABLE IF NOT EXISTS polls (
    id         INTEGER PRIMARY KEY AUTOINCREMENT,
    question   TEXT    NOT NULL,
    is_public  INTEGER NOT NULL DEFAULT 1,
    created_at TEXT    NOT NULL
);

CREATE TABLE IF NOT EXISTS poll_options (
    id         INTEGER PRIMARY KEY AUTOINCREMENT,
    poll_id    INTEGER NOT NULL,
    label      TEXT    NOT NULL,
    sort_order INTEGER NOT NULL DEFAULT 0,
    FOREIGN KEY (poll_id) REFERENCES polls(id) ON DELETE CASCADE
);

CREATE TABLE IF NOT EXISTS votes (
    id         INTEGER PRIMARY KEY AUTOINCREMENT,
    poll_id    INTEGER NOT NULL,
    option_id  INTEGER NOT NULL,
    user_id    INTEGER NOT NULL,
    created_at TEXT    NOT NULL,
    UNIQUE (poll_id, user_id),  -- One vote per user per poll
    FOREIGN KEY (poll_id) REFERENCES polls(id) ON DELETE CASCADE,
    FOREIGN KEY (option_id) REFERENCES poll_options(id) ON DELETE CASCADE
);

CREATE INDEX IF NOT EXISTS idx_votes_poll ON votes (poll_id, option_id);

Endpoints

Method	Path	Auth	Description
POST	/polls	Admin	Create poll with options
GET	/polls/{id}	Public	Get poll (private → 404 for non-admin)
POST	/polls/{id}/vote	User	Cast vote
GET	/polls/{id}/results	Public	Get result counts per option

Option Validation

private const int MIN_OPTIONS   = 2;
private const int MAX_OPTIONS   = 20;
private const int MAX_LABEL_LEN = 100;

foreach ($rawOptions as $idx => $label) {
    if (!is_string($label) || trim($label) === '') {
        return $this->problem(422, 'validation-failed', "options[{$idx}] must not be empty.");
    }
    if (strlen($label) > self::MAX_LABEL_LEN) {
        return $this->problem(422, 'validation-failed', "options[{$idx}] too long (max 100).");
    }
}

Duplicate Vote Prevention

/** @return 'ok'|'already_voted'|'invalid_option' */
public function vote(int $pollId, int $userId, int $optionId): string
{
    // Verify option belongs to poll (prevents cross-poll option injection)
    $stmt = $this->pdo->prepare(
        'SELECT id FROM poll_options WHERE id = :oid AND poll_id = :pid'
    );
    $stmt->execute([':oid' => $optionId, ':pid' => $pollId]);
    if ($stmt->fetch() === false) {
        return 'invalid_option'; // → 422
    }

    // Check for existing vote
    $stmt2 = $this->pdo->prepare(
        'SELECT id FROM votes WHERE poll_id = :pid AND user_id = :uid'
    );
    if ($stmt2->fetch() !== false) {
        return 'already_voted'; // → 409
    }

    // INSERT — UNIQUE(poll_id, user_id) constraint is a safety net
    $this->pdo->prepare('INSERT INTO votes ...')->execute([...]);
    return 'ok';
}

Result Aggregation

Using LEFT JOIN ensures options with zero votes still appear in results:

SELECT o.id, o.label, o.sort_order,
       COUNT(v.id) AS votes
FROM poll_options o
LEFT JOIN votes v ON v.option_id = o.id AND v.poll_id = o.poll_id
WHERE o.poll_id = :pid
GROUP BY o.id, o.label, o.sort_order
ORDER BY o.sort_order ASC, o.id ASC

$results    = $this->repo->results($id);
$totalVotes = array_sum(array_column($results, 'votes'));

return $this->json([
    'poll_id'     => $id,
    'total_votes' => $totalVotes,
    'results'     => $results,
]);

Private Poll Access Control

Private polls return 404 for non-admin users (existence hiding):

// GET /polls/{id}
if (!(bool) $poll['is_public'] && !$this->isAdmin($req)) {
    return $this->problem(404, 'not-found', 'Poll not found.');
}

Security Patterns

• Admin fail-closed: if ($this->adminKey === '') return false; before hash_equals()
• is_int(): Strict type check for option_id — rejects floats/strings
• ctype_digit(): ReDoS-safe integer validation for path IDs
• Cross-poll option injection: WHERE id = :oid AND poll_id = :pid prevents using option from different poll
• is_bool(): Strict check for is_public flag — rejects 1/0/"true" etc.