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database.sql

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+-- --------------------------------------------------------
+-- Host:                         202.46.28.160
+-- Server version:               PostgreSQL 17.5 (Debian 17.5-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
+-- Server OS:                    
+-- HeidiSQL Version:             12.10.0.7000
+-- --------------------------------------------------------
+
+/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
+/*!40101 SET NAMES  */;
+/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
+/*!40103 SET TIME_ZONE='+00:00' */;
+/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
+/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
+/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
+
+-- Data exporting was unselected.
+
+-- Data exporting was unselected.
+
+-- Data exporting was unselected.
+
+/*!40103 SET TIME_ZONE=IFNULL(@OLD_TIME_ZONE, 'system') */;
+/*!40101 SET SQL_MODE=IFNULL(@OLD_SQL_MODE, '') */;
+/*!40014 SET FOREIGN_KEY_CHECKS=IFNULL(@OLD_FOREIGN_KEY_CHECKS, 1) */;
+/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
+/*!40111 SET SQL_NOTES=IFNULL(@OLD_SQL_NOTES, 1) */;

enrollment.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+var (
+	IdempotencyStore = make(map[string]string)
+	mu               sync.Mutex
+)
+
+func EnrollCourseIdempotent(key string) string {
+	mu.Lock()
+	if val, ok := IdempotencyStore[key]; ok {
+		mu.Unlock()
+		return fmt.Sprintf("Hasil cache: %s", val)
+	}
+	mu.Unlock()
+
+	// proses baru
+	fmt.Println("Memproses enrollment baru...")
+	time.Sleep(1500 * time.Millisecond)
+
+	result := "Enrollment berhasil untuk " + key
+
+	mu.Lock()
+	IdempotencyStore[key] = result
+	mu.Unlock()
+
+	return result
+}

go.mod

@@ -0,0 +1,5 @@
+module 07-06-Melvin-Goroutine
+
+go 1.25.1
+
+require github.com/lib/pq v1.10.9

go.sum

@@ -0,0 +1,2 @@
+github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
+github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=

pool_manager.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"time"
+
+	_ "github.com/lib/pq"
+)
+
+var DB *sql.DB
+
+func InitDB() {
+	dbURL := "postgres://5803024006:5803024006@202.46.28.160:45432/tgs03_5803024006?sslmode=disable"
+
+	var err error
+	DB, err = sql.Open("postgres", dbURL)
+	if err != nil {
+		panic(err)
+	}
+
+	// setting pool
+	DB.SetMaxOpenConns(10)
+	DB.SetMaxIdleConns(5)
+	DB.SetConnMaxLifetime(time.Minute * 5)
+
+	// test koneksi
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
+	defer cancel()
+	if err = DB.PingContext(ctx); err != nil {
+		panic(fmt.Sprintf("gagal koneksi database: %v", err))
+	}
+
+	fmt.Println("✅ Database connected!")
+}
+
+// ===== CRUD Contoh =====
+
+func CreateUser(name, email string) (int, error) {
+	var id int
+	err := DB.QueryRow(`INSERT INTO users (name, email) VALUES ($1, $2) RETURNING id`, name, email).Scan(&id)
+	return id, err
+}
+
+func CreateCourse(title, desc string) (int, error) {
+	var id int
+	err := DB.QueryRow(`INSERT INTO courses (title, description) VALUES ($1, $2) RETURNING id`, title, desc).Scan(&id)
+	return id, err
+}
+
+func EnrollUser(userID, courseID int) error {
+	_, err := DB.Exec(`INSERT INTO enrollments (user_id, course_id) VALUES ($1, $2) ON CONFLICT (user_id, course_id) DO NOTHING`, userID, courseID)
+	return err
+}
+
+func ListEnrollments() error {
+	rows, err := DB.Query(`SELECT u.name, c.title, e.created_at 
+                           FROM enrollments e
+                           JOIN users u ON e.user_id = u.id
+                           JOIN courses c ON e.course_id = c.id`)
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+
+	fmt.Println("=== Enrollments ===")
+	for rows.Next() {
+		var name, title string
+		var created time.Time
+		_ = rows.Scan(&name, &title, &created)
+		fmt.Printf("%s enrolled in %s at %v\n", name, title, created)
+	}
+	return nil
+}