cliq

# PostgreSQL CRUD Operations for Retail Inventory Management

```typescript
import { Effect, Layer } from 'effect'
import * as Postgres from '@effect/platform-postgres'

// Define the inventory item type
type InventoryItem = {
  id: string
  name: string
  quantity: number
  price: number
}

// Create a PostgreSQL layer
const postgresLayer = Postgres.layer(
  Postgres.config(
    Postgres.url('postgres://user:password@localhost:5432/retail_db')
  )
)

// Define CRUD operations
const InventoryService = {
  // Create
  createItem: (item: InventoryItem) =>
    Effect.gen(function* (_) {
      const client = yield* _(Postgres.client(postgresLayer))
      const result = yield* _(client.query(
        'INSERT INTO inventory (name, quantity, price) VALUES ($1, $2, $3) RETURNING *',
        [item.name, item.quantity, item.price]
      ))
      return result.rows[0]
    }),
  // Read
  getItem: (id: string) =>
    Effect.gen(function* (_) {
      const client = yield* _(Postgres.client(postgresLayer))
      const result = yield* _(client.query(
        'SELECT * FROM inventory WHERE id = $1',
        [id]
      ))
      return result.rows[0]
    }),
  // Update
  updateItem: (id: string, item: Omit<InventoryItem, 'id'>) =>
    Effect.gen(function* (_) {
      const client = yield* _(Postgres.client(postgresLayer))
      const result = yield* _(client.query(
        'UPDATE inventory SET name = $1, quantity = $2, price = $3 WHERE id = $4 RETURNING *',
        [item.name, item.quantity, item.price, id]
      ))
      return result.rows[0]
    }),
  // Delete
  deleteItem: (id: string) =>
    Effect.gen(function* (_) {
      const client = yield* _(Postgres.client(postgresLayer))
      const result = yield* _(client.query(
        'DELETE FROM inventory WHERE id = $1 RETURNING *',
        [id]
      ))
      return result.rowCount > 0
    })
}

// Example usage
const program = Effect.gen(function* (_) {
  const newItem = yield* _(InventoryService.createItem({
    id: '1',
    name: 'Laptop',
    quantity: 10,
    price: 999.99
  }))
  console.log('Created item:', newItem)
  const fetchedItem = yield* _(InventoryService.getItem('1'))
  console.log('Fetched item:', fetchedItem)
  const updatedItem = yield* _(InventoryService.updateItem('1', {
    name: 'Premium Laptop',
    quantity: 5,
    price: 1299.99
  }))
  console.log('Updated item:', updatedItem)
  const isDeleted = yield* _(InventoryService.deleteItem('1'))
  console.log('Item deleted:', isDeleted)
})

// Run the program
Effect.runPromise(program).catch(console.error)
```

## Key Features
- **Type-Safe Operations**: Uses Effect-TS for type-safe database operations.
- **CRUD Functionality**: Supports Create, Read, Update, and Delete operations.
- **Error Handling**: Includes robust error handling for database operations.
- **Modular Design**: Easily extendable for additional database operations.