Scala Play 2.5 表单 bindFromRequest : Cannot find any HTTP Request here?

Question

我有一个这样实现的 Controller 操作:

def doChangePassword = deadbolt.Restrict(List(Array(Application.USER_ROLE_KEY)))() 
{ request => // <<<<<<<<<<<< here is the request 
  Future {
    val context = JavaHelpers.createJavaContext(request)
    com.feth.play.module.pa.controllers.AuthenticateBase.noCache(context.response())

    val filledForm = Account.PasswordChangeForm.bindFromRequest
    // compilation error here, it can't see the request ^^^^^^^

    if (filledForm.hasErrors) {
      // User did not select whether to link or not link
      BadRequest(views.html.account.password_change(userService, filledForm))
    } else {
      val Some(user: UserRow) = userService.getUser(context.session)
      val newPassword = filledForm.get.password
      userService.changePassword(user, new MyUsernamePasswordAuthUser(newPassword), true)
      Redirect(routes.Application.profile).flashing(
        Application.FLASH_MESSAGE_KEY -> messagesApi.preferred(request)("playauthenticate.change_password.success")
      )
    }
  }
}

上面的实现导致编译错误:

[error] /home/bravegag/code/play-authenticate-usage-scala/app/controllers/Account.scala:74: Cannot find any HTTP Request here
[error]         val filledForm =  Account.PasswordChangeForm.bindFromRequest
[error]                                                     ^
[error] one error found

但是，如果我将第 2 行更改为:

{ request => // <<<<<<<<<<<< here is the request 

到

{ implicit request => // <<<<<<<<<<<< here is the request 

然后它编译......但为什么呢？

Answer 1

您要找的是Implicit Parameters .简而言之:

隐式参数可以像常规或显式参数一样传递。如果您没有明确提供隐式参数，那么编译器将尝试为您传递一个。隐式可以来自不同的地方。来自常见问题 Where does Scala look for implicits? :

1. First look in current scope
   • Implicits defined in current scope
   • Explicit imports
   • wildcard imports
2. Now look at associated types in
   • Companion objects of a type
   • Implicit scope of an argument’s type (2.9.1)
   • Implicit scope of type arguments (2.8.0)
   • Outer objects for nested types
   • Other dimensions

第 1 项下的隐式优先于第 2 项下的那些。

通过标记 request如 implicit在您的示例中，您声明了“在当前范围内隐式定义”。您需要有一个隐式请求，因为 bindFormRequest “要求”你通过一个。看它的签名:

bindFromRequest()(implicit request: Request[_]): Form[T]

现在你有一个 implicit request在作用域中，编译器会自动将其传递给 bindFormRequerst .

正如我在开头提到的，您也可以通过 request明确地:

val filledForm = Account.PasswordChangeForm.bindFromRequest()(request)

在后一种情况下，无需声明 request如 implicit因为你显然是路过 request明确地。两种变体是相同的。这取决于你喜欢哪一种。