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+{# retoor <retoor@molodetz.nl> #}
+{% extends 'page.html' %}
+
+{% set page_title = "Database Application" %}
+{% set breadcrumb = [{"url": "tutorials/index.html", "title": "Tutorials"}, {"title": "Database App"}] %}
+{% set prev_page = {"url": "tutorials/websocket-chat.html", "title": "WebSocket Chat"} %}
+{% set next_page = {"url": "tutorials/template-rendering.html", "title": "Template Rendering"} %}
+
+{% block article %}
+                <h1>Database Application</h1>
+
+                <p>In this tutorial, you will build a complete task management application using SQLite for persistent storage. You will learn to create tables, perform CRUD operations, and build a command-line interface.</p>
+
+                <h2>What You Will Learn</h2>
+
+                <ul>
+                    <li>Creating and managing SQLite databases</li>
+                    <li>Designing database schemas</li>
+                    <li>Performing CRUD operations (Create, Read, Update, Delete)</li>
+                    <li>Using parameterized queries to prevent SQL injection</li>
+                    <li>Building a command-line interface</li>
+                </ul>
+
+                <h2>Step 1: Setting Up the Database</h2>
+
+                <p>Create a file called <code>task_app.wren</code>:</p>
+
+                <pre><code>import "sqlite" for Sqlite
+
+var db = Sqlite.open("tasks.db")
+
+db.execute("
+    CREATE TABLE IF NOT EXISTS tasks (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        title TEXT NOT NULL,
+        description TEXT,
+        priority INTEGER DEFAULT 1,
+        completed INTEGER DEFAULT 0,
+        created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+        due_date DATE
+    )
+")
+
+System.print("Database initialized!")
+db.close()</code></pre>
+
+                <h2>Step 2: Creating a Task Model</h2>
+
+                <p>Let's create a class to manage task operations:</p>
+
+                <pre><code>import "sqlite" for Sqlite
+import "datetime" for DateTime
+
+class TaskManager {
+    construct new(dbPath) {
+        _db = Sqlite.open(dbPath)
+        initDatabase()
+    }
+
+    initDatabase() {
+        _db.execute("
+            CREATE TABLE IF NOT EXISTS tasks (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                title TEXT NOT NULL,
+                description TEXT,
+                priority INTEGER DEFAULT 1,
+                completed INTEGER DEFAULT 0,
+                created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+                due_date DATE
+            )
+        ")
+    }
+
+    create(title, description, priority, dueDate) {
+        _db.execute(
+            "INSERT INTO tasks (title, description, priority, due_date) VALUES (?, ?, ?, ?)",
+            [title, description, priority, dueDate]
+        )
+        return _db.lastInsertId
+    }
+
+    findAll() {
+        return _db.execute("SELECT * FROM tasks ORDER BY priority DESC, due_date ASC")
+    }
+
+    findById(id) {
+        var results = _db.execute("SELECT * FROM tasks WHERE id = ?", [id])
+        return results.count > 0 ? results[0] : null
+    }
+
+    findPending() {
+        return _db.execute("SELECT * FROM tasks WHERE completed = 0 ORDER BY priority DESC")
+    }
+
+    findCompleted() {
+        return _db.execute("SELECT * FROM tasks WHERE completed = 1 ORDER BY created_at DESC")
+    }
+
+    update(id, title, description, priority, dueDate) {
+        _db.execute(
+            "UPDATE tasks SET title = ?, description = ?, priority = ?, due_date = ? WHERE id = ?",
+            [title, description, priority, dueDate, id]
+        )
+    }
+
+    complete(id) {
+        _db.execute("UPDATE tasks SET completed = 1 WHERE id = ?", [id])
+    }
+
+    uncomplete(id) {
+        _db.execute("UPDATE tasks SET completed = 0 WHERE id = ?", [id])
+    }
+
+    delete(id) {
+        _db.execute("DELETE FROM tasks WHERE id = ?", [id])
+    }
+
+    search(query) {
+        return _db.execute(
+            "SELECT * FROM tasks WHERE title LIKE ? OR description LIKE ?",
+            ["\%%(query)\%", "\%%(query)\%"]
+        )
+    }
+
+    close() {
+        _db.close()
+    }
+}
+
+var tasks = TaskManager.new("tasks.db")
+
+var id = tasks.create("Learn Wren-CLI", "Complete the database tutorial", 3, "2024-12-31")
+System.print("Created task with ID: %(id)")
+
+tasks.close()</code></pre>
+
+                <h2>Step 3: Building the CLI Interface</h2>
+
+                <p>Now let's create an interactive command-line interface:</p>
+
+                <pre><code>import "sqlite" for Sqlite
+import "io" for Stdin
+
+class TaskManager {
+    construct new(dbPath) {
+        _db = Sqlite.open(dbPath)
+        initDatabase()
+    }
+
+    initDatabase() {
+        _db.execute("
+            CREATE TABLE IF NOT EXISTS tasks (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                title TEXT NOT NULL,
+                description TEXT,
+                priority INTEGER DEFAULT 1,
+                completed INTEGER DEFAULT 0,
+                created_at DATETIME DEFAULT CURRENT_TIMESTAMP
+            )
+        ")
+    }
+
+    create(title, description, priority) {
+        _db.execute(
+            "INSERT INTO tasks (title, description, priority) VALUES (?, ?, ?)",
+            [title, description, priority]
+        )
+        return _db.lastInsertId
+    }
+
+    findAll() {
+        return _db.execute("SELECT * FROM tasks ORDER BY completed ASC, priority DESC")
+    }
+
+    complete(id) {
+        _db.execute("UPDATE tasks SET completed = 1 WHERE id = ?", [id])
+    }
+
+    delete(id) {
+        _db.execute("DELETE FROM tasks WHERE id = ?", [id])
+    }
+
+    close() {
+        _db.close()
+    }
+}
+
+class TaskApp {
+    construct new() {
+        _tasks = TaskManager.new("tasks.db")
+        _running = true
+    }
+
+    run() {
+        System.print("=== Task Manager ===\n")
+        showHelp()
+
+        while (_running) {
+            System.write("\n> ")
+            var input = Stdin.readLine()
+
+            if (input == null) break
+
+            var parts = input.split(" ")
+            var command = parts.count > 0 ? parts[0] : ""
+
+            if (command == "list") {
+                listTasks()
+            } else if (command == "add") {
+                addTask()
+            } else if (command == "done") {
+                if (parts.count > 1) {
+                    completeTask(Num.fromString(parts[1]))
+                } else {
+                    System.print("Usage: done <id>")
+                }
+            } else if (command == "delete") {
+                if (parts.count > 1) {
+                    deleteTask(Num.fromString(parts[1]))
+                } else {
+                    System.print("Usage: delete <id>")
+                }
+            } else if (command == "help") {
+                showHelp()
+            } else if (command == "quit" || command == "exit") {
+                _running = false
+            } else if (command.count > 0) {
+                System.print("Unknown command: %(command)")
+            }
+        }
+
+        _tasks.close()
+        System.print("Goodbye!")
+    }
+
+    showHelp() {
+        System.print("Commands:")
+        System.print("  list          - Show all tasks")
+        System.print("  add           - Add a new task")
+        System.print("  done <id>     - Mark task as complete")
+        System.print("  delete <id>   - Delete a task")
+        System.print("  help          - Show this help")
+        System.print("  quit          - Exit the application")
+    }
+
+    listTasks() {
+        var tasks = _tasks.findAll()
+
+        if (tasks.count == 0) {
+            System.print("No tasks found.")
+            return
+        }
+
+        System.print("\nID  | Pri | Status | Title")
+        System.print("----|-----|--------|------")
+
+        for (task in tasks) {
+            var status = task["completed"] == 1 ? "[X]" : "[ ]"
+            var priority = ["Low", "Med", "High"][task["priority"] - 1]
+            System.print("%(task["id"])   | %(priority) | %(status)    | %(task["title"])")
+        }
+    }
+
+    addTask() {
+        System.write("Title: ")
+        var title = Stdin.readLine()
+
+        System.write("Description (optional): ")
+        var description = Stdin.readLine()
+
+        System.write("Priority (1=Low, 2=Medium, 3=High): ")
+        var priorityStr = Stdin.readLine()
+        var priority = Num.fromString(priorityStr) || 1
+
+        if (priority < 1) priority = 1
+        if (priority > 3) priority = 3
+
+        var id = _tasks.create(title, description, priority)
+        System.print("Task created with ID: %(id)")
+    }
+
+    completeTask(id) {
+        _tasks.complete(id)
+        System.print("Task %(id) marked as complete.")
+    }
+
+    deleteTask(id) {
+        _tasks.delete(id)
+        System.print("Task %(id) deleted.")
+    }
+}
+
+var app = TaskApp.new()
+app.run()</code></pre>
+
+                <h2>Step 4: Adding Advanced Features</h2>
+
+                <p>Let's enhance our application with categories and due dates:</p>
+
+                <pre><code>import "sqlite" for Sqlite
+import "io" for Stdin
+import "datetime" for DateTime
+
+class TaskManager {
+    construct new(dbPath) {
+        _db = Sqlite.open(dbPath)
+        initDatabase()
+    }
+
+    initDatabase() {
+        _db.execute("
+            CREATE TABLE IF NOT EXISTS categories (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                name TEXT NOT NULL UNIQUE,
+                color TEXT DEFAULT '#808080'
+            )
+        ")
+
+        _db.execute("
+            CREATE TABLE IF NOT EXISTS tasks (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                title TEXT NOT NULL,
+                description TEXT,
+                category_id INTEGER,
+                priority INTEGER DEFAULT 1,
+                completed INTEGER DEFAULT 0,
+                created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+                due_date DATE,
+                FOREIGN KEY (category_id) REFERENCES categories(id)
+            )
+        ")
+
+        var categories = _db.execute("SELECT COUNT(*) as count FROM categories")
+        if (categories[0]["count"] == 0) {
+            _db.execute("INSERT INTO categories (name, color) VALUES ('Work', '#FF6B6B')")
+            _db.execute("INSERT INTO categories (name, color) VALUES ('Personal', '#4ECDC4')")
+            _db.execute("INSERT INTO categories (name, color) VALUES ('Shopping', '#45B7D1')")
+        }
+    }
+
+    createTask(title, description, categoryId, priority, dueDate) {
+        _db.execute(
+            "INSERT INTO tasks (title, description, category_id, priority, due_date) VALUES (?, ?, ?, ?, ?)",
+            [title, description, categoryId, priority, dueDate]
+        )
+        return _db.lastInsertId
+    }
+
+    findAllTasks() {
+        return _db.execute("
+            SELECT t.*, c.name as category_name
+            FROM tasks t
+            LEFT JOIN categories c ON t.category_id = c.id
+            ORDER BY t.completed ASC, t.priority DESC, t.due_date ASC
+        ")
+    }
+
+    findTasksByCategory(categoryId) {
+        return _db.execute("
+            SELECT t.*, c.name as category_name
+            FROM tasks t
+            LEFT JOIN categories c ON t.category_id = c.id
+            WHERE t.category_id = ?
+            ORDER BY t.completed ASC, t.priority DESC
+        ", [categoryId])
+    }
+
+    findOverdueTasks() {
+        return _db.execute("
+            SELECT t.*, c.name as category_name
+            FROM tasks t
+            LEFT JOIN categories c ON t.category_id = c.id
+            WHERE t.completed = 0 AND t.due_date < DATE('now')
+            ORDER BY t.due_date ASC
+        ")
+    }
+
+    findDueToday() {
+        return _db.execute("
+            SELECT t.*, c.name as category_name
+            FROM tasks t
+            LEFT JOIN categories c ON t.category_id = c.id
+            WHERE t.completed = 0 AND t.due_date = DATE('now')
+            ORDER BY t.priority DESC
+        ")
+    }
+
+    findCategories() {
+        return _db.execute("SELECT * FROM categories ORDER BY name")
+    }
+
+    createCategory(name, color) {
+        _db.execute("INSERT INTO categories (name, color) VALUES (?, ?)", [name, color])
+        return _db.lastInsertId
+    }
+
+    completeTask(id) {
+        _db.execute("UPDATE tasks SET completed = 1 WHERE id = ?", [id])
+    }
+
+    deleteTask(id) {
+        _db.execute("DELETE FROM tasks WHERE id = ?", [id])
+    }
+
+    getStats() {
+        var total = _db.execute("SELECT COUNT(*) as count FROM tasks")[0]["count"]
+        var completed = _db.execute("SELECT COUNT(*) as count FROM tasks WHERE completed = 1")[0]["count"]
+        var pending = total - completed
+        var overdue = _db.execute("SELECT COUNT(*) as count FROM tasks WHERE completed = 0 AND due_date < DATE('now')")[0]["count"]
+
+        return {
+            "total": total,
+            "completed": completed,
+            "pending": pending,
+            "overdue": overdue
+        }
+    }
+
+    close() {
+        _db.close()
+    }
+}
+
+class TaskApp {
+    construct new() {
+        _tasks = TaskManager.new("tasks.db")
+        _running = true
+    }
+
+    run() {
+        System.print("=== Task Manager v2 ===\n")
+
+        while (_running) {
+            showMenu()
+            System.write("\nChoice: ")
+            var choice = Stdin.readLine()
+
+            if (choice == "1") {
+                listTasks()
+            } else if (choice == "2") {
+                addTask()
+            } else if (choice == "3") {
+                completeTask()
+            } else if (choice == "4") {
+                showOverdue()
+            } else if (choice == "5") {
+                showStats()
+            } else if (choice == "6") {
+                manageCategories()
+            } else if (choice == "0") {
+                _running = false
+            }
+        }
+
+        _tasks.close()
+        System.print("\nGoodbye!")
+    }
+
+    showMenu() {
+        System.print("\n--- Main Menu ---")
+        System.print("1. List all tasks")
+        System.print("2. Add new task")
+        System.print("3. Complete task")
+        System.print("4. Show overdue")
+        System.print("5. Statistics")
+        System.print("6. Categories")
+        System.print("0. Exit")
+    }
+
+    listTasks() {
+        var tasks = _tasks.findAllTasks()
+
+        if (tasks.count == 0) {
+            System.print("\nNo tasks found.")
+            return
+        }
+
+        System.print("\n--- All Tasks ---")
+        for (task in tasks) {
+            var status = task["completed"] == 1 ? "[X]" : "[ ]"
+            var category = task["category_name"] || "None"
+            var due = task["due_date"] || "No due date"
+
+            System.print("%(task["id"]). %(status) %(task["title"])")
+            System.print("   Category: %(category) | Due: %(due)")
+        }
+    }
+
+    addTask() {
+        System.print("\n--- Add Task ---")
+
+        System.write("Title: ")
+        var title = Stdin.readLine()
+        if (title.count == 0) return
+
+        System.write("Description: ")
+        var description = Stdin.readLine()
+
+        var categories = _tasks.findCategories()
+        System.print("\nCategories:")
+        for (cat in categories) {
+            System.print("  %(cat["id"]). %(cat["name"])")
+        }
+        System.write("Category ID (or 0 for none): ")
+        var categoryId = Num.fromString(Stdin.readLine())
+        if (categoryId == 0) categoryId = null
+
+        System.write("Priority (1-3): ")
+        var priority = Num.fromString(Stdin.readLine()) || 1
+
+        System.write("Due date (YYYY-MM-DD or empty): ")
+        var dueDate = Stdin.readLine()
+        if (dueDate.count == 0) dueDate = null
+
+        var id = _tasks.createTask(title, description, categoryId, priority, dueDate)
+        System.print("\nTask created with ID: %(id)")
+    }
+
+    completeTask() {
+        System.write("\nTask ID to complete: ")
+        var id = Num.fromString(Stdin.readLine())
+        if (id) {
+            _tasks.completeTask(id)
+            System.print("Task %(id) marked as complete!")
+        }
+    }
+
+    showOverdue() {
+        var tasks = _tasks.findOverdueTasks()
+
+        if (tasks.count == 0) {
+            System.print("\nNo overdue tasks!")
+            return
+        }
+
+        System.print("\n--- Overdue Tasks ---")
+        for (task in tasks) {
+            System.print("%(task["id"]). %(task["title"]) (Due: %(task["due_date"]))")
+        }
+    }
+
+    showStats() {
+        var stats = _tasks.getStats()
+
+        System.print("\n--- Statistics ---")
+        System.print("Total tasks:     %(stats["total"])")
+        System.print("Completed:       %(stats["completed"])")
+        System.print("Pending:         %(stats["pending"])")
+        System.print("Overdue:         %(stats["overdue"])")
+
+        if (stats["total"] > 0) {
+            var pct = (stats["completed"] / stats["total"] * 100).round
+            System.print("Completion rate: %(pct)\%")
+        }
+    }
+
+    manageCategories() {
+        var categories = _tasks.findCategories()
+
+        System.print("\n--- Categories ---")
+        for (cat in categories) {
+            System.print("%(cat["id"]). %(cat["name"])")
+        }
+
+        System.write("\nAdd new category? (y/n): ")
+        if (Stdin.readLine().lower == "y") {
+            System.write("Category name: ")
+            var name = Stdin.readLine()
+            if (name.count > 0) {
+                _tasks.createCategory(name, "#808080")
+                System.print("Category created!")
+            }
+        }
+    }
+}
+
+var app = TaskApp.new()
+app.run()</code></pre>
+
+                <h2>Running the Application</h2>
+
+                <pre><code>$ wren_cli task_app.wren
+=== Task Manager v2 ===
+
+--- Main Menu ---
+1. List all tasks
+2. Add new task
+3. Complete task
+4. Show overdue
+5. Statistics
+6. Categories
+0. Exit
+
+Choice: 2
+
+--- Add Task ---
+Title: Complete database tutorial
+Description: Learn SQLite with Wren-CLI
+
+Categories:
+  1. Work
+  2. Personal
+  3. Shopping
+Category ID (or 0 for none): 1
+Priority (1-3): 3
+Due date (YYYY-MM-DD or empty): 2024-12-31
+
+Task created with ID: 1</code></pre>
+
+                <div class="admonition tip">
+                    <div class="admonition-title">Tip</div>
+                    <p>Always use parameterized queries with <code>?</code> placeholders instead of string concatenation. This prevents SQL injection vulnerabilities.</p>
+                </div>
+
+                <div class="admonition note">
+                    <div class="admonition-title">Note</div>
+                    <p>Use <code>":memory:"</code> as the database path for testing without creating a file on disk.</p>
+                </div>
+
+                <h2>Next Steps</h2>
+
+                <ul>
+                    <li>Add data export to JSON or CSV</li>
+                    <li>Implement task reminders with <a href="../api/timer.html">Timer</a></li>
+                    <li>Generate HTML reports with <a href="template-rendering.html">Jinja templates</a></li>
+                    <li>See the <a href="../api/sqlite.html">SQLite API reference</a></li>
+                </ul>
+{% endblock %}