Rails 4: Insert Attribute Into Params

In Rails 3, it was possible to insert an attribute into params like so:

params[:post][:user_id] = current_user.id

I'm attempting to do something similar in Rails 4, but having no luck:

post_params[:user_id] = current_user.id

. . . .


private

  def post_params
    params.require(:post).permit(:user_id)
  end

Rails is ignoring this insertion. It doesn't throw any errors, it just quietly fails.

Found the answer here. Rather than inserting the attribute from within the controller action, you can insert it into the params definition with a merge. To expand upon my previous example:

private

  def post_params
    params.require(:post).permit(:some_attribute).merge(user_id: current_user.id)
  end

In addition to @timothycommoner's answer, you can alternatively perform the merge on a per-action basis:

  def create
    @post = Post.new(post_params.merge(user_id: current_user.id))
    # save the object etc
  end

private
  def post_params
    params.require(:post).permit(:some_attribute)
  end

As an alternative for this case, you can required pass attribute via scope:

current_user.posts.create(post_params)

If anyone is trying to figure out how to add/edit a nested attribute in a Rails 5 attributes hash, I found this to be the most straight-forward (alternate) approach. Don't bother with merge or deep_merge...it's a pain due to the strong parameters. In this example, I needed to copy the group_id and vendor_id to the associated invoice (nested parameters) prior to saving.

def create
  my_params = order_params
  @order = Order.new
  @order.attributes = my_params
  @order.invoice.group_id = my_params[:group_id]
  @order.invoice.vendor_id = my_params[:vendor_id]
  @order.save
end

private

# Permit like normal
def order_params
  params.require(:order).permit([:vendor_id, :group_id, :amount, :shipping,:invoice_attributes => [:invoice_number, :invoice_date, :due_date, :vendor_id, :group_id]])
end