Context

GORM’s context support, enabled by the WithContext method, is a powerful feature that enhances the flexibility and control of database operations in Go applications. Let’s delve into these various aspects:

シングルセッション

Single session mode is appropriate for executing individual operations. It ensures that the specific operation is executed within the context’s scope, allowing for better control and monitoring.

db.WithContext(ctx).Find(&users)

Continuous Session Mode

Continuous session mode is ideal for performing a series of related operations. It maintains the context across these operations, which is particularly useful in scenarios like transactions.

tx := db.WithContext(ctx)
tx.First(&user, 1)
tx.Model(&user).Update("role", "admin")

Context Timeout

Setting a timeout on the context passed to db.WithContext can control the duration of long-running queries. This is crucial for maintaining performance and avoiding resource lock-ups in database interactions.

ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
defer cancel()

db.WithContext(ctx).Find(&users)

Hooks/Callbacks内でのcontextの使用

The context can also be accessed within GORM’s hooks/callbacks. This enables contextual information to be used during these lifecycle events.

func (u *User) BeforeCreate(tx *gorm.DB) (err error) {
  ctx := tx.Statement.Context
  // ... use context
  return
}

Integration with Chi Middleware

GORM’s context support extends to web server middlewares, such as those in the Chi router. This allows setting a context with a timeout for all database operations within the scope of a web request.

func SetDBMiddleware(next http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    timeoutContext, _ := context.WithTimeout(context.Background(), time.Second)
    ctx := context.WithValue(r.Context(), "DB", db.WithContext(timeoutContext))
    next.ServeHTTP(w, r.WithContext(ctx))
  })
}

// Router setup
r := chi.NewRouter()
r.Use(SetDBMiddleware)

// Route handlers
r.Get("/", func(w http.ResponseWriter, r *http.Request) {
  db, ok := r.Context().Value("DB").(*gorm.DB)
  // ... db operations
})

r.Get("/user", func(w http.ResponseWriter, r *http.Request) {
  db, ok := r.Context().Value("DB").(*gorm.DB)
  // ... db operations
})

Note: Setting the Context with WithContext is goroutine-safe. This ensures that database operations are safely managed across multiple goroutines. For more details, refer to the Session documentation in GORM.

Logger Integration

GORM’s logger also accepts Context, which can be used for log tracking and integrating with existing logging infrastructures.

詳細については、 Logger を参照してください。