can you review this code and tell if there is any issues or improvements todo
```
datasource db {
  provider = "mongodb"
  url      = env("DATABASE_URL")
}

generator client {
  provider = "prisma-client-js"
}

// User management and authentication
model User {
  id            String    @id @default(auto()) @map("_id") @db.ObjectId
  name          String    @unique
  username      String    @unique
  password      String    // Hashed password
  role          UserRole  @default(CASHIER)
  createdAt     DateTime  @default(now())
  updatedAt     DateTime  @updatedAt
  isActive      Boolean   @default(true)
  
  // Relations
  shifts        Shift[]
  sales         Sale[]
  stockAdjustments StockAdjustment[]
  notifications Notification[]
}

enum UserRole {
  ADMIN
  PHARMACIST
  CASHIER
}

// Product and inventory management
model Product {
  id            String    @id @default(auto()) @map("_id") @db.ObjectId
  barcode       String    @unique
  name          String
  description   String?
  category      Category  @relation(fields: [categoryId], references: [id])
  categoryId    String    @db.ObjectId
  supplier      Supplier  @relation(fields: [supplierId], references: [id])
  supplierId    String    @db.ObjectId
  price         Float
  costPrice     Float
  minStockLevel Int
  createdAt     DateTime  @default(now())
  updatedAt     DateTime  @updatedAt
  isActive      Boolean   @default(true)

  // Relations
  inventory     Inventory[]
  saleItems     SaleItem[]
  stockAdjustments StockAdjustment[]
}

model Category {
  id          String    @id @default(auto()) @map("_id") @db.ObjectId
  name        String    @unique
  description String?
  products    Product[]
  createdAt   DateTime  @default(now())
  updatedAt   DateTime  @updatedAt
}

model Supplier {
  id          String    @id @default(auto()) @map("_id") @db.ObjectId
  name        String
  email       String    @unique
  phone       String
  address     String
  products    Product[]
  createdAt   DateTime  @default(now())
  updatedAt   DateTime  @updatedAt
}

// Inventory tracking
model Inventory {
  id          String    @id @default(auto()) @map("_id") @db.ObjectId
  product     Product   @relation(fields: [productId], references: [id])
  productId   String    @db.ObjectId
  batchNumber String
  quantity    Int
  expiryDate  DateTime
  createdAt   DateTime  @default(now())
  updatedAt   DateTime  @updatedAt
}

// Sales and transactions
model Sale {
  id          String    @id @default(auto()) @map("_id") @db.ObjectId
  saleNumber  String    @unique
  cashier     User      @relation(fields: [cashierId], references: [id])
  cashierId   String    @db.ObjectId
  items       SaleItem[]
  totalAmount Float
  paymentType PaymentType
  createdAt   DateTime  @default(now())
  updatedAt   DateTime  @updatedAt
}

model SaleItem {
  id          String    @id @default(auto()) @map("_id") @db.ObjectId
  sale        Sale      @relation(fields: [saleId], references: [id])
  saleId      String    @db.ObjectId
  product     Product   @relation(fields: [productId], references: [id])
  productId   String    @db.ObjectId
  quantity    Int
  unitPrice   Float
  totalPrice  Float
  createdAt   DateTime  @default(now())
}

enum PaymentType {
  CASH
  CARD
  MOBILE
}

// Stock adjustments and tracking
model StockAdjustment {
  id          String    @id @default(auto()) @map("_id") @db.ObjectId
  product     Product   @relation(fields: [productId], references: [id])
  productId   String    @db.ObjectId
  adjustedBy  User      @relation(fields: [userId], references: [id])
  userId      String    @db.ObjectId
  quantity    Int
  type        AdjustmentType
  reason      String
  createdAt   DateTime  @default(now())
}

enum AdjustmentType {
  ADDITION
  REDUCTION
  CORRECTION
}

// Shift management
model Shift {
  id          String    @id @default(auto()) @map("_id") @db.ObjectId
  user        User      @relation(fields: [userId], references: [id])
  userId      String    @db.ObjectId
  startTime   DateTime
  endTime     DateTime?
  status      ShiftStatus @default(ACTIVE)
  createdAt   DateTime  @default(now())
  updatedAt   DateTime  @updatedAt
}

enum ShiftStatus {
  ACTIVE
  COMPLETED
  CANCELLED
}

// Notifications and alerts
model Notification {
  id          String    @id @default(auto()) @map("_id") @db.ObjectId
  user        User      @relation(fields: [userId], references: [id])
  userId      String    @db.ObjectId
  type        NotificationType
  message     String
  isRead      Boolean   @default(false)
  createdAt   DateTime  @default(now())
}

enum NotificationType {
  LOW_STOCK
  EXPIRY_WARNING
  SALES_SUMMARY
  SYSTEM
}
```