Use a singleton for database connections #36
Description
Per the comments in db.go
// TODO: Turn this into a singleton class.
// Only one database connection should be created and used throughout the application.
Implementation of a singleton may look like
import (
"fmt"
"log"
"sync"
"github.com/glebarez/sqlite"
"gorm.io/driver/postgres"
"gorm.io/gorm"
"gorm.io/gorm/logger"
)
const DB_SQLITE_FALLBACK_WARNING = "[db] DATABASE_URL not set – falling back to embedded SQLite ./mcp.db"
const DB_SQLITE_CONN_STRING = "mcp.db?_busy_timeout=5000&_journal_mode=WAL"
var db *gorm.DB
var err error
var once sync.Once
// NewDBConnection creates a new database connection based on the provided DSN.
// If the DSN is empty, it falls back to an embedded SQLite database at "./mcp.db".
func NewDBConnection(dsnString string) (*gorm.DB, error) {
var dbErr error
once.Do(func() {
var dialector gorm.Dialector
if dsnString == "" {
log.Println(DB_SQLITE_FALLBACK_WARNING)
dialector = sqlite.Open(DB_SQLITE_CONN_STRING)
} else {
dialector = postgres.Open(dsnString)
}
c := &gorm.Config{
Logger: logger.Default.LogMode(logger.Silent),
}
db, err = gorm.Open(dialector, c)
if err != nil {
dbErr = fmt.Errorf("failed to connect to database: %w", err)
}
})
if dbErr != nil {
return nil, dbErr
}
return db, err
}Because the signature does not change, there should be no refactoring implementations. However it could stand to use a test:
package db
import (
"os"
"testing"
)
func TestNewDBConnection_SQLiteFallback(t *testing.T) {
// Unset DATABASE_URL to force fallback
os.Unsetenv("DATABASE_URL")
db, err := NewDBConnection("")
if err != nil {
t.Fatalf("expected no error, got: %v", err)
}
if db == nil {
t.Fatal("expected db instance, got nil")
}
}
func TestNewDBConnection_PostgresDSN(t *testing.T) {
// Use a fake DSN, expect connection error
db, err := NewDBConnection("postgres://invalid:invalid@localhost:5432/invalid?sslmode=disable")
if err == nil {
t.Error("expected error for invalid DSN, got nil")
}
if db != nil {
t.Error("expected nil db for invalid DSN")
}
}