diff --git a/src/main/java/dev/dao/MenuItemDao.java b/src/main/java/dev/dao/MenuItemDao.java
index 3bbebe9..9ee7e5c 100644
--- a/src/main/java/dev/dao/MenuItemDao.java
+++ b/src/main/java/dev/dao/MenuItemDao.java
@@ -1,24 +1,73 @@
 package dev.dao;
 
+import dev.database.DatabaseConnection;
 import dev.model.MenuItem;
 
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.util.ArrayList;
 import java.util.List;
 
 public class MenuItemDao {
 
     public List<MenuItem> findAll() {
 
-        // TODO:
-        // Retrieve all menu items
+        String sql = "SELECT * FROM menu_items";
+        List<MenuItem> items = new ArrayList<>();
 
-        return null;
+        try (PreparedStatement ps = DatabaseConnection
+                                    .getConnection()
+                                    .prepareStatement(sql))
+        {
+            ResultSet rs = ps.executeQuery();
+            while (rs.next())
+            {
+                MenuItem menuItem = new MenuItem();
+                menuItem.setId(rs.getInt("id"));
+                menuItem.setName(rs.getString("name"));
+                menuItem.setDescription(rs.getString("description"));
+                menuItem.setPrice(rs.getDouble("price"));
+                menuItem.setCategory(rs.getString("category"));
+
+                items.add(menuItem);
+            }
+
+        } catch (SQLException e) {
+
+            System.out.println(e.getStackTrace());
+        }
+
+        return items;
     }
 
     public MenuItem findById(int id) {
 
-        // TODO:
-        // Find menu item by id
+        String sql = "SELECT * FROM menu_items WHERE id=?";
 
+        try(PreparedStatement ps = DatabaseConnection
+                .getConnection()
+                .prepareStatement(sql))
+        {
+            ps.setInt(1,id);
+            ResultSet rs = ps.executeQuery();
+
+            if(rs.next())
+            {
+                MenuItem item = new MenuItem();
+                item.setId(rs.getInt("id"));
+                item.setName(rs.getString("name"));
+                item.setDescription(rs.getString("description"));
+                item.setPrice(rs.getDouble("price"));
+                item.setCategory(rs.getString("category"));
+
+                return item;
+            }
+        }
+        catch (SQLException e)
+        {
+            e.printStackTrace();
+        }
         return null;
     }
 
diff --git a/src/main/java/dev/dao/OrderDao.java b/src/main/java/dev/dao/OrderDao.java
index 00999a2..99c13a7 100644
--- a/src/main/java/dev/dao/OrderDao.java
+++ b/src/main/java/dev/dao/OrderDao.java
@@ -1,25 +1,75 @@
 package dev.dao;
 
+import dev.database.DatabaseConnection;
 import dev.model.Order;
 
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Timestamp;
+import java.util.ArrayList;
 import java.util.List;
 
 public class OrderDao {
 
     public int save(Order order) {
 
-        // TODO:
-        // Insert order and return generated id
+        String sql = "INSERT INTO user_orders(user_id, created_at, total_price) VALUES(?,?,?)";
+
+
+        try (PreparedStatement ps = DatabaseConnection
+                                    .getConnection()
+                                    .prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS))
+        {
+
+            ps.setInt(1, order.getUserId());
+            ps.setTimestamp(2, Timestamp.valueOf(order.getCreatedAt()));
+            ps.setDouble(3, order.getTotalPrice());
+
+            ps.executeUpdate();
+            ResultSet rs = ps.getGeneratedKeys();
+
+            if(rs.next()) return rs.getInt(1);
+
+        } catch (SQLException e) {
+
+            e.printStackTrace();
+        }
 
         return -1;
     }
 
     public List<Order> findByUserId(int userId) {
 
-        // TODO:
-        // Retrieve all orders of a user
+        List<Order> orders = new ArrayList<>();
+        String sql = "SELECT * FROM user_orders WHERE user_id=?";
 
-        return null;
+        try(PreparedStatement ps = DatabaseConnection
+                                    .getConnection()
+                                    .prepareStatement(sql))
+
+        {
+            ps.setInt(1,userId);
+            ResultSet rs = ps.executeQuery();
+
+            while(rs.next())
+            {
+
+                Order order = new Order();
+
+                order.setId(rs.getInt("id"));
+                order.setUserId(rs.getInt("user_id"));
+                order.setTotalPrice(rs.getDouble("total_price"));
+                order.setCreatedAt(rs.getTimestamp("created_at").toLocalDateTime());
+
+                orders.add(order);
+            }
+        }
+        catch (SQLException e)
+        {
+            e.printStackTrace();
+        }
+        return orders;
     }
 
 }
\ No newline at end of file
diff --git a/src/main/java/dev/dao/OrderDetailDao.java b/src/main/java/dev/dao/OrderDetailDao.java
index ed42f56..534cade 100644
--- a/src/main/java/dev/dao/OrderDetailDao.java
+++ b/src/main/java/dev/dao/OrderDetailDao.java
@@ -1,24 +1,70 @@
 package dev.dao;
 
+import dev.database.DatabaseConnection;
+
 import dev.model.OrderDetail;
 
+
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.util.ArrayList;
 import java.util.List;
 
 public class OrderDetailDao {
 
     public void save(OrderDetail detail) {
 
-        // TODO:
-        // Insert order detail
+        String sql = "INSERT INTO order_details (order_id, menu_id, quantity, item_price) VALUES (?,?,?,?)";
+
+        try (PreparedStatement ps = DatabaseConnection
+                                    .getConnection()
+                                    .prepareStatement(sql))
+        {
+            ps.setInt(1,detail.getOrderId());
+            ps.setInt(2,detail.getMenuItemId());
+            ps.setInt(3,detail.getQuantity());
+            ps.setDouble(4,detail.getPrice());
+
+            ps.executeUpdate();
+
+        } catch (SQLException e) {
+
+            System.out.println(e.getStackTrace());
+        }
 
     }
 
     public List<OrderDetail> findByOrderId(int orderId) {
 
-        // TODO:
-        // Retrieve order details
+       String sql = "SELECT * FROM order_details WHERE order_id=?";
 
-        return null;
+        List<OrderDetail> details = new ArrayList<>();
+
+       try (PreparedStatement ps = DatabaseConnection
+                                    .getConnection()
+                                    .prepareStatement(sql))
+       {
+           ps.setInt(1,orderId);
+           ResultSet rs = ps.executeQuery();
+
+           while(rs.next())
+           {
+               OrderDetail detail = new OrderDetail();
+
+               detail.setOrderId(rs.getInt("order_id"));
+               detail.setMenuItemId(rs.getInt("menu_id"));
+               detail.setPrice(rs.getDouble("item_price"));
+               detail.setQuantity(rs.getInt("quantity"));
+
+               details.add(detail);
+           }
+
+       } catch (SQLException e) {
+           System.out.println(e.getStackTrace());
+       }
+
+        return details;
     }
 
 }
\ No newline at end of file
diff --git a/src/main/java/dev/dao/UserDao.java b/src/main/java/dev/dao/UserDao.java
index af08106..88bf342 100644
--- a/src/main/java/dev/dao/UserDao.java
+++ b/src/main/java/dev/dao/UserDao.java
@@ -1,23 +1,58 @@
 package dev.dao;
 
+import dev.database.DatabaseConnection;
 import dev.model.User;
 
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+
 public class UserDao {
 
     public boolean save(User user) {
 
-        // TODO:
-        // Insert user into database
+        String sql = "INSERT INTO users (username, password_hash, email) VALUES (?, ?, ?)";
+
+        try {
+            PreparedStatement ps = DatabaseConnection.getConnection().prepareStatement(sql);
+            ps.setString(1, user.getUsername());
+            ps.setString(2, user.getPasswordHash());
+            ps.setString(3, user.getEmail());
+            ps.executeUpdate();
+            return true;
+        } catch (SQLException e) {
+
+            System.out.println("fail to save user: " + e.getMessage());
+        }
 
         return false;
     }
 
     public User findByUsername(String username) {
 
-        // TODO:
-        // Find a user by username
+        String sql = "SELECT * FROM users WHERE username=?";
 
-        return null;
+        User result = null;
+
+
+        try {
+            PreparedStatement stmt = DatabaseConnection.getConnection().prepareStatement(sql);
+            stmt.setString(1, username);
+
+            ResultSet rs = stmt.executeQuery();
+
+            if (rs.next()){
+                result = new User(
+                        rs.getInt("id"),
+                        rs.getString("username"),
+                        rs.getString("password_hash"),
+                        rs.getString("email")
+                );
+            }
+        } catch (SQLException e) {
+            System.err.println("Unable to find user: " + e.getMessage());
+        }
+        return result;
     }
 
 }
\ No newline at end of file