您如何在Rails 4中访问params [：model] [：field]？

Question

From what I understand...

• If you have a form_for @model , params[:model] is available when the form is submitted. Furthermore, if the form has 2 attributes attr1 and attr2 , params[:model][:attr1] and params[:model][:attr2] are available when the form is submitted.
• In Rails 4, you're supposed to write a method model_params that says params.require(:model).permit(:attr1, :attr2) .
• You'd then use model_params like so: Model.new(model_params) .

However, what do you do if you only need one of the fields from the form? Like if you only needed params[:model][:attr1] ?

Example:

def create
  @user = User.new(user_params)
  if @user.save
    # need access to params[:user][:password] here
    redirect_to root_url, :notice => "Signed up!"
  else
    render :new
  end
end

private

    def user_params
        params.require(:user).permit(:email, :password, :password_confirmation)
    end

Answer 1

The gem responsible for this behaviour is strong_parameters . The permit() method decides what to pass on to the model based on the attributes you pass to it.

In your case, you passed it :attr1 and :attr2 :

params.require(:model).permit(:attr1, :attr2)

This means the model will have attr1 and attr2 set to whatever values were passed from the form.

If you only wanted to set attr1 , just remove attr2 from the permit() call.

params.require(:model).permit(:attr1)

You model will not have attr1 set, but not attr2 . It's that simple.

You can even permit everything (not recommended) by calling permit! with a bang and no arguments.

You can read more about this behaviour on the gem's Github project page .

Update based on the OP's edit

If you need access to params[:user][:password] in the controller... well, you just accessed it in your example. You accessed it by typing params[:user][:password] .

Nothing prevents you from accessing the params hash directly. strong_parameter's job is to prevent you from mass assigning a hash to a model, that's all.