I’ll help you understand **Slot PG in Deno**. Slot PG refers to using the **PostgreSQL client library** for Deno, typically the popular `postgres` or `postgres.js` library adapted for Deno.
## **Popular PostgreSQL Libraries for Deno**
### 1. **`postgres` (postgres.js)**
The most popular PostgreSQL client for Deno:
“`typescript
import postgres from “https://deno.land/x/[email protected]/mod.ts”;
// Create connection pool
const pool = new postgres.Pool({
hostname: “localhost”,
port: 5432,
database: “testdb”,
user: “user”,
password: “password”,
max: 20, // max connections
}, 10); // connection timeout
// Using the pool
const connection = await pool.connect();
try {
const result = await connection.queryObject`SELECT * FROM users WHERE id = ${1}`;
console.log(result.rows);
} finally {
connection.release();
}
“`
### 2. **`deno-postgres`**
Another popular option:
“`typescript
import { Client } from “https://deno.land/x/[email protected]/mod.ts”;
const client = new Client({
user: “user”,
database: “testdb”,
hostname: “localhost”,
port: 5432,
});
await client.connect();
// Query with parameters
const result = await client.queryArray(
“SELECT * FROM users WHERE age > $1”,
[18]
);
console.log(result.rows);
await client.end();
“`
## **Complete Example: CRUD Operations**
“`typescript
import { Client } from “https://deno.land/x/postgres/mod.ts”;
interface User {
id: number;
name: string;
email: string;
}
class DatabaseService {
private client: Client;
constructor() {
this.client = new Client({
hostname: “localhost”,
port: 5432,
user: “postgres”,
password: “password”,
database: “myapp”,
});
}
async connect() {
await this.client.connect();
}
async disconnect() {
await this.client.end();
}
// Create
async createUser(name: string, email: string): Promise
const result = await this.client.queryObject
`INSERT INTO users (name, email) VALUES ($1, $2) RETURNING *`,
[name, email]
);
return result.rows[0];
}
// Read
async getUsers(): Promise
const result = await this.client.queryObject
“SELECT * FROM users”
);
return result.rows;
}
// Update
async updateUser(id: number, name: string): Promise
const result = await this.client.queryObject
`UPDATE users SET name = $1 WHERE id = $2 RETURNING *`,
[name, id]
);
return result.rows[0];
}
// Delete
async deleteUser(id: number): Promise
await this.client.queryObject(
“DELETE FROM users WHERE id = $1”,
[id]
);
}
}
// Usage
const db = new DatabaseService();
await db.connect();
const newUser = await db.createUser(“John Doe”, “[email protected]”);
console.log(newUser);
const users = await db.getUsers();
console.log(users);
await db.disconnect();
“`
## **Connection Pooling Example**
“`typescript
import { Pool } from “https://deno.land/x/[email protected]/mod.ts”;
const pool = new Pool({
hostname: “localhost”,
port: 5432,
user: “postgres”,
password: “password”,
database: “testdb”,
max: 10, // maximum number of clients
idleTimeoutMillis: 10000,
}, 10);
async function queryWithPool() {
const client = await pool.connect();
try {
// Transaction example
await client.queryObject(“BEGIN”);
const userResult = await client.queryObject(
“INSERT INTO users (name) VALUES ($1) RETURNING id”,
[“Alice”]
);
const userId = userResult.rows[0].id;
await client.queryObject(
“INSERT INTO profiles (user_id, bio) VALUES ($1, $2)”,
[userId, “Software Developer”]
);
await client.queryObject(“COMMIT”);
} catch (error) {
await client.queryObject(“ROLLBACK”);
throw error;
} finally {
client.release();
}
}
// Run multiple queries concurrently
const promises = Array.from({ length: 5 }, (_, i) =>
queryWithPool()
);
await Promise.all(promises);
// Cleanup
await pool.end();
“`
## **Environment Configuration**
“`typescript
// config.ts
import { load } from “https://deno.land/[email protected]/dotenv/mod.ts”;
const env = await load();
export const dbConfig = {
hostname: env[“DB_HOST”] || “localhost”,
port: parseInt(env[“DB_PORT”] || “5432”),
user: env[“DB_USER”] || “postgres”,
password: env[“DB_PASSWORD”] || “”,
database: env[“DB_NAME”] || “deno_app”,
max: parseInt(env[“DB_POOL_MAX”] || “10”),
};
“`
## **Migration Setup**
Create a simple migration system:
“`typescript
// migrations/001_create_users.sql
CREATE TABLE IF NOT EXISTS users (
id SERIAL PRIMARY KEY,
name VARCHAR(100) NOT NULL,
email VARCHAR(255) UNIQUE NOT NULL,
created_at TIMESTAMP DEFAULT NOW()
);
// migrate.ts
import { Client } from “https://deno.land/x/postgres/mod.ts”;
async function runMigration() {
const client = new Client({
hostname: “localhost”,
port: 5432,
user: “postgres”,
password: “password”,
database: “myapp”,
});
await client.connect();
const migrationSQL = await Deno.readTextFile(
“./migrations/001_create_users.sql”
);
await client.queryArray(migrationSQL);
console.log(“Migration completed!”);
await client.end();
}
runMigration().catch(console.error);
“`
## **Best Practices**
1. **Use connection pooling** for web applications
2. **Always release connections** back to the pool
3. **Use parameterized queries** to prevent SQL injection
4. **Handle transactions properly** with BEGIN/COMMIT/ROLLBACK
5. **Close connections** when your application shuts down
6. **Use environment variables** for configuration
## **Installation and Running**
“`bash
# Run with PostgreSQL client
deno run –allow-net –allow-read –allow-env app.ts
# Or with all permissions (development only)
deno run -A app.ts
“`
## **Alternative: Using Deno Fresh Framework with PostgreSQL**
“`typescript
// routes/api/users.ts
import { Handlers } from “$fresh/server.ts”;
import { Pool } from “https://deno.land/x/[email protected]/mod.ts”;
const pool = new Pool({
hostname: Deno.env.get(“DB_HOST”),
database: Deno.env.get(“DB_NAME”),
user: Deno.env.get(“DB_USER”),
password: Deno.env.get(“DB_PASSWORD”),
}, 10);
export const handler: Handlers = {
async GET(req) {
const client = await pool.connect();
try {
const result = await client.queryObject(“SELECT * FROM users”);
return new Response(JSON.stringify(result.rows), {
headers: { “Content-Type”: “application/json” },
});
} finally {
client.release();
}
},
};
“`
This should give you a comprehensive understanding of using PostgreSQL (Slot PG) with Deno. The `postgres` library is the most feature-complete and actively maintained option for Deno.
