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+# DatabaseService Usage Examples
+
+This document shows how to refactor existing code to use the new `DatabaseService` class for cleaner, more maintainable database operations.
+
+## Current State
+
+Files are using the procedural MySQLi pattern:
+```php
+$stmt = $conn->prepare("SELECT * FROM users WHERE email = ?");
+$stmt->bind_param("s", $email);
+$stmt->execute();
+$result = $stmt->get_result();
+$row = $result->fetch_assoc();
+$stmt->close();
+```
+
+## Example 1: Simple SELECT (admin_members.php)
+
+### Current Code
+```php
+$stmt = $conn->prepare("SELECT user_id, first_name, last_name, tel_cell, email, dob, accept_indemnity FROM membership_application");
+$stmt->execute();
+$result = $stmt->get_result();
+
+// Then in HTML/JS loop:
+while ($row = $result->fetch_assoc()) {
+    // display row
+}
+```
+
+### Using DatabaseService
+```php
+// Simple - get all records
+$members = $db->select("SELECT user_id, first_name, last_name, tel_cell, email, dob, accept_indemnity FROM membership_application");
+
+// In HTML/JS loop:
+foreach ($members as $row) {
+    // display row
+}
+```
+
+**Benefits:**
+- No manual `bind_param()`, `execute()`, `close()` needed
+- Returns array directly
+- Automatic error tracking via `$db->getLastError()`
+
+---
+
+## Example 2: SELECT with Parameters (validate_login.php)
+
+### Current Code
+```php
+$query = "SELECT * FROM users WHERE email = ?";
+$stmt = $conn->prepare($query);
+$stmt->bind_param("s", $email);
+$stmt->execute();
+$result = $stmt->get_result();
+
+if ($result->num_rows == 1) {
+    $row = $result->fetch_assoc();
+    // use $row
+}
+$stmt->close();
+```
+
+### Using DatabaseService
+```php
+$user = $db->selectOne(
+    "SELECT * FROM users WHERE email = ?",
+    [$email],
+    "s"  // s = string type
+);
+
+if ($user) {
+    // use $user - returns false if no row found
+}
+```
+
+**Benefits:**
+- One-liner for single row
+- Handles null checks automatically
+- Type specification clear in parameters
+
+---
+
+## Example 3: INSERT (validate_login.php)
+
+### Current Code
+```php
+$query = "INSERT INTO users (email, first_name, last_name, profile_pic, password, is_verified) VALUES (?, ?, ?, ?, ?, ?)";
+$stmt = $conn->prepare($query);
+$is_verified = 1;
+$stmt->bind_param("sssssi", $email, $first_name, $last_name, $picture, $password, $is_verified);
+if ($stmt->execute()) {
+    $user_id = $conn->insert_id;  // ❌ Bug: insert_id from $conn, not $stmt
+    // use $user_id
+}
+$stmt->close();
+```
+
+### Using DatabaseService
+```php
+$user_id = $db->insert(
+    "INSERT INTO users (email, first_name, last_name, profile_pic, password, is_verified) VALUES (?, ?, ?, ?, ?, ?)",
+    [$email, $first_name, $last_name, $picture, $password, 1],
+    "sssssi"
+);
+
+if ($user_id) {
+    // $user_id contains the auto-increment ID
+} else {
+    $error = $db->getLastError();
+}
+```
+
+**Benefits:**
+- Returns insert ID directly
+- Automatic error handling
+- Cleaner parameter list
+
+---
+
+## Example 4: UPDATE (admin_members.php)
+
+### Current Code
+```php
+$user_id = intval($_POST['user_id']);
+$stmt = $conn->prepare("UPDATE membership_application SET accept_indemnity = 1 WHERE user_id = ?");
+if ($stmt) {
+    $stmt->bind_param("i", $user_id);
+    $stmt->execute();
+    $stmt->close();
+}
+```
+
+### Using DatabaseService
+```php
+$user_id = intval($_POST['user_id']);
+$affectedRows = $db->update(
+    "UPDATE membership_application SET accept_indemnity = 1 WHERE user_id = ?",
+    [$user_id],
+    "i"
+);
+
+if ($affectedRows !== false) {
+    // Updated successfully, $affectedRows = number of rows changed
+}
+```
+
+**Benefits:**
+- Returns affected row count
+- No manual statement closing
+- Error available via `$db->getLastError()`
+
+---
+
+## Example 5: COUNT / EXISTS
+
+### Current Pattern (Need 3 lines)
+```php
+$stmt = $conn->prepare("SELECT COUNT(*) as count FROM users WHERE email = ?");
+$stmt->bind_param("s", $email);
+$stmt->execute();
+$result = $stmt->get_result();
+$row = $result->fetch_assoc();
+if ($row['count'] > 0) { /* exists */ }
+$stmt->close();
+```
+
+### Using DatabaseService (One line)
+```php
+$exists = $db->exists("users", "email = ?", [$email], "s");
+if ($exists) {
+    // User exists
+}
+```
+
+**Benefits:**
+- Boolean result
+- Intent is clear
+- One-liner
+
+---
+
+## Example 6: Multiple Rows with Filtering
+
+### Current Code
+```php
+$status = 'active';
+$stmt = $conn->prepare("SELECT * FROM members WHERE status = ? ORDER BY last_name ASC");
+$stmt->bind_param("s", $status);
+$stmt->execute();
+$result = $stmt->get_result();
+$members = [];
+while ($row = $result->fetch_assoc()) {
+    $members[] = $row;
+}
+$stmt->close();
+```
+
+### Using DatabaseService
+```php
+$members = $db->select(
+    "SELECT * FROM members WHERE status = ? ORDER BY last_name ASC",
+    ['active'],
+    "s"
+);
+```
+
+**Benefits:**
+- Returns array directly
+- No loop needed
+- 2 lines vs 8 lines
+
+---
+
+## Example 7: Error Handling
+
+### Current Pattern
+```php
+$stmt = $conn->prepare("SELECT * FROM users WHERE id = ?");
+if (!$stmt) {
+    echo "Prepare failed: " . $conn->error;
+    exit();
+}
+$stmt->bind_param("i", $id);
+if (!$stmt->execute()) {
+    echo "Execute failed: " . $stmt->error;
+    exit();
+}
+```
+
+### Using DatabaseService
+```php
+$user = $db->selectOne("SELECT * FROM users WHERE id = ?", [$id], "i");
+if ($user === false) {
+    $error = $db->getLastError();
+    error_log("Database error: " . $error);
+    // handle error
+}
+```
+
+**Benefits:**
+- Error handling centralized
+- No null checks for each step
+- Debug via `$db->getLastQuery()`
+
+---
+
+## Example 8: Transactions
+
+### Current Pattern
+```php
+$conn->begin_transaction();
+try {
+    $stmt = $conn->prepare("INSERT INTO orders ...");
+    $stmt->execute();
+    
+    $stmt = $conn->prepare("UPDATE inventory ...");
+    $stmt->execute();
+    
+    $conn->commit();
+} catch (Exception $e) {
+    $conn->rollback();
+}
+```
+
+### Using DatabaseService
+```php
+$db->beginTransaction();
+
+$order_id = $db->insert("INSERT INTO orders ...", [...], "...");
+if ($order_id === false) {
+    $db->rollback();
+    exit("Order creation failed");
+}
+
+$updated = $db->update("UPDATE inventory ...", [...], "...");
+if ($updated === false) {
+    $db->rollback();
+    exit("Inventory update failed");
+}
+
+$db->commit();
+```
+
+**Benefits:**
+- Unified transaction API
+- Built-in error checking
+- Clean rollback on failure
+
+---
+
+## Type Specification Reference
+
+When using DatabaseService methods, specify parameter types:
+
+| Type | Meaning | Example |
+|------|---------|---------|
+| `"i"` | Integer | `user_id = 5` |
+| `"d"` | Double/Float | `price = 19.99` |
+| `"s"` | String | `email = 'test@example.com'` |
+| `"b"` | Blob | Binary data |
+
+Examples:
+```php
+// Single parameter
+$db->select("SELECT * FROM users WHERE id = ?", [123], "i");
+
+// Multiple parameters
+$db->select(
+    "SELECT * FROM users WHERE email = ? AND status = ?", 
+    ["test@example.com", "active"], 
+    "ss"
+);
+
+// Mixed types
+$db->select(
+    "SELECT * FROM orders WHERE user_id = ? AND total > ? AND date = ?",
+    [5, 100.50, "2025-01-01"],
+    "ids"  // integer, double, string
+);
+```
+
+---
+
+## Migration Path
+
+### Phase 1: New Code
+Start using `$db` for all new features and AJAX endpoints.
+
+### Phase 2: High-Traffic Files
+Refactor popular files:
+1. `validate_login.php` - Login is critical
+2. `functions.php` - Helper functions
+3. `admin_members.php`, `admin_payments.php` - Admin pages
+
+### Phase 3: Gradual Rollout
+As each file is refactored, commit and test thoroughly before moving to next.
+
+### Phase 4: Full Migration
+Eventually all procedural `$conn->prepare()` patterns replaced.
+
+---
+
+## Benefits Summary
+
+| Aspect | Before | After |
+|--------|--------|-------|
+| Lines per query | 5-8 | 1-3 |
+| Error handling | Manual checks | Automatic |
+| Type safety | bind_param() | Parameter array |
+| Statement closing | Manual | Automatic |
+| Insert ID handling | `$conn->insert_id` (buggy) | Direct return |
+| Debugging | Check multiple vars | `getLastError()`, `getLastQuery()` |
+| Consistency | Varies | Unified API |
+
+---
+
+## Next Steps
+
+1. Start with one file (e.g., `admin_members.php`)
+2. Convert simple queries first
+3. Test thoroughly
+4. Commit and move to next file
+5. Keep `$conn` available for complex queries that don't fit the standard patterns
+
+The `$db` service makes your code **cleaner, safer, and easier to maintain**.