Attendance Processing

Process student attendance through QR code scanning with automatic status calculation based on class schedules.

QR Code Scanner

Page: scanner.php Authentication: Teacher session required Library: Instascan.js for camera-based QR code scanning

Scanner Implementation

let scanner = new Instascan.Scanner({ 
    video: document.getElementById('preview') 
});

scanner.addListener('scan', function (content) {
    // Send scanned data to process_attendance.php
    fetch('process_attendance.php', {
        method: 'POST',
        headers: {
            'Content-Type': 'application/x-www-form-urlencoded',
        },
        body: 'qr_data=' + encodeURIComponent(content)
    })
    .then(response => response.text())
    .then(data => {
        document.getElementById('result').innerHTML = data;
    });
});

Camera Selection

Instascan.Camera.getCameras().then(function (cameras) {
    if (cameras.length > 0) {
        scanner.start(cameras[0]); // Use first available camera
    } else {
        console.error('No cameras found.');
    }
});

The scanner uses the device’s camera to read QR codes. Camera permissions must be granted by the user.

Process Attendance

Endpoint: process_attendance.php Method: POST Authentication: Teacher session required

Request Parameters

qr_data

string

required

Student ID from scanned QR code

Processing Flow

Authentication Check:

if (!isset($_SESSION['user_type']) || 
    $_SESSION['user_type'] !== 'teacher' || 
    !isset($_SESSION['teacher_id'])) {
    echo "❌ Unauthorized access";
    exit;
}

Student Verification:

SELECT cs.class_id, s.* 
FROM students s
JOIN class_students cs ON s.student_id = cs.student_id 
JOIN classes c ON cs.class_id = c.id
WHERE s.student_id = ? AND c.teacher_id = ?

Schedule Verification:

SELECT cs.* 
FROM class_schedules cs
JOIN classes c ON cs.class_id = c.id
WHERE c.teacher_id = ? 
AND cs.class_id = ?
AND cs.day_of_week = DAYOFWEEK(CURRENT_DATE())

Duplicate Check:

SELECT * FROM attendance 
WHERE student_id = ? 
AND class_id = ? 
AND date = CURRENT_DATE()

Status Calculation & Recording

Attendance Status Calculation

Algorithm: Determines if student is on-time or late based on schedule

Time Comparison Logic

// Get current time
$currentTime = new DateTime();

// Get class start time
$startTime = new DateTime($schedule['start_time']);

// Calculate grace time (start + grace period)
$graceTime = clone $startTime;
$graceTime->modify('+' . $schedule['grace_period'] . ' minutes');

// Determine status
$status = $currentTime <= $graceTime ? 'on-time' : 'late';

Status Values

on-time

string

Student checked in at or before start_time + grace_period

late

string

Student checked in after start_time + grace_period

absent

string

Student did not check in (manually set by teacher or system)

Example Calculation

Schedule:

Start Time: 09:00 AM
Grace Period: 15 minutes
Late After: 09:15 AM

Check-in Times:

08:55 AM → on-time
09:00 AM → on-time
09:10 AM → on-time
09:15 AM → on-time
09:16 AM → late
09:30 AM → late

Grace period is inclusive. Students checking in exactly at the grace time cutoff are marked on-time.

Record Attendance

Database Operation:

INSERT INTO attendance (student_id, class_id, date, time, status) 
VALUES (?, ?, CURRENT_DATE(), CURRENT_TIME(), ?)

Attendance Record Fields

student_id

string

Student identifier from QR code

class_id

integer

ID of the class from schedule

date

Current date (CURRENT_DATE())

time

Current time (CURRENT_TIME())

status

string

Calculated status: ‘on-time’ or ‘late’

Response Messages

Success Responses

On-time Attendance:

✅ On-time attendance marked for Student ID: 12345

Late Attendance:

⚠️ Late attendance marked for Student ID: 12345

Error Responses

Unauthorized:

❌ Unauthorized access

Student Not Found:

❌ Student not found in any of your classes

No Schedule:

❌ No class scheduled for today with this teacher

Already Marked:

⚠️ Attendance already marked for this class today

Database Error:

Error: [PDOException message]

Validation Rules

1. Teacher Authorization

Only logged-in teachers can process attendance. Student sessions are rejected.

if ($_SESSION['user_type'] !== 'teacher') {
    echo "❌ Unauthorized access";
    exit;
}

2. Student-Teacher Relationship

Student must be enrolled in one of the teacher’s classes:

WHERE s.student_id = ? AND c.teacher_id = ?

3. Schedule Validation

Class must be scheduled for the current day:

WHERE cs.day_of_week = DAYOFWEEK(CURRENT_DATE())

Day Mapping:

1 = Sunday
2 = Monday
3 = Tuesday
4 = Wednesday
5 = Thursday
6 = Friday
7 = Saturday

4. Duplicate Prevention

Only one attendance record per student per class per day:

SELECT * FROM attendance 
WHERE student_id = ? 
AND class_id = ? 
AND date = CURRENT_DATE()

Complete Processing Example

Scenario

Student: ID 12345
Teacher: T1234
Class: Computer Science 101
Schedule: Monday 09:00 AM, Grace Period: 15 minutes
Check-in Time: 09:10 AM

Processing Steps

QR Scan: Student shows QR code containing “12345”
Teacher Auth: Verified T1234 is logged in
Student Lookup: Found student 12345 in CS101 (teacher T1234’s class)
Schedule Check: CS101 scheduled for Monday at 09:00 AM
Duplicate Check: No attendance record for today
Status Calc:
- Current: 09:10 AM
- Grace: 09:15 AM
- Status: on-time ✅
Record: Insert attendance record
Response: ”✅ On-time attendance marked for Student ID: 12345”

Database Record

INSERT INTO attendance 
(student_id, class_id, date, time, status) 
VALUES 
('12345', 1, '2026-03-03', '09:10:00', 'on-time')

Manual Status Updates

Teachers can manually update attendance status through the dashboard: Endpoint: teacher_dashboard.php (POST)

update_status

string

required

Set to “1”

attendance_id

integer

required

ID of attendance record to update

new_status

string

required

New status: ‘on-time’, ‘late’, or ‘absent’

Update Query

UPDATE attendance 
SET status = ? 
WHERE id = ?

Verification:

SELECT a.id 
FROM attendance a
JOIN classes c ON a.class_id = c.id
WHERE a.id = ? AND c.teacher_id = ?

Manual updates allow teachers to correct attendance status if a student was marked incorrectly.

Error Handling

All database operations are wrapped in try-catch blocks:

try {
    // Process attendance
    $stmt = $pdo->prepare("...");
    $stmt->execute([...]);
} catch(PDOException $e) {
    echo "Error: " . $e->getMessage();
}

Common Errors

Invalid Student ID:

Student doesn’t exist in database
Student not enrolled in any teacher’s classes

Schedule Issues:

No schedule set for class
Class not scheduled for current day

Database Errors:

Connection failures
Constraint violations
Transaction rollbacks

Always validate all inputs and check for existing records before inserting new attendance data.

Core Components

Database Schema

QR Code Scanner

Scanner Implementation

Camera Selection

Process Attendance

Request Parameters

Processing Flow

Attendance Status Calculation

Time Comparison Logic

Status Values

Example Calculation

Record Attendance

Attendance Record Fields

Response Messages

Success Responses

Error Responses

Validation Rules

1. Teacher Authorization

2. Student-Teacher Relationship

3. Schedule Validation

4. Duplicate Prevention

Complete Processing Example

Scenario

Processing Steps

Database Record

Manual Status Updates

Update Query

Error Handling

Common Errors

Build docs developers (and LLMs) love

Core Components

Database Schema

​QR Code Scanner

​Scanner Implementation

​Camera Selection

​Process Attendance

​Request Parameters

​Processing Flow

​Attendance Status Calculation

​Time Comparison Logic

​Status Values

​Example Calculation

​Record Attendance

​Attendance Record Fields

​Response Messages

​Success Responses

​Error Responses

​Validation Rules

​1. Teacher Authorization

​2. Student-Teacher Relationship

​3. Schedule Validation

​4. Duplicate Prevention

​Complete Processing Example

​Scenario

​Processing Steps

​Database Record

​Manual Status Updates

​Update Query

​Error Handling

​Common Errors

Build docs developers (and LLMs) love

QR Code Scanner

Scanner Implementation

Camera Selection

Process Attendance

Request Parameters

Processing Flow

Attendance Status Calculation

Time Comparison Logic

Status Values

Example Calculation

Record Attendance

Attendance Record Fields

Response Messages

Success Responses

Error Responses

Validation Rules

1. Teacher Authorization

2. Student-Teacher Relationship

3. Schedule Validation

4. Duplicate Prevention

Complete Processing Example

Scenario

Processing Steps

Database Record

Manual Status Updates

Update Query

Error Handling

Common Errors