The forme_set plugin remembers columns from another form on the same page

[janko]

I have two forms for an Expense records, one for updating the amount, the other for updating the note describing the expense. The first form has only the field for the amount, while the second has only the field for the note. However, when I render both forms on the same page, and submit the second one, it tries to nullify the amount field.

Here is a self-contained example demonstrating this issue:

require "roda"
require "sequel"
require "capybara"

DB = Sequel.sqlite
DB.create_table :expenses do
  primary_key :id
  Float :amount, null: false
  String :note, null: false
end

class Expense < Sequel::Model
  plugin :forme_set
end

Expense.create(amount: 123, note: "Description")

class App < Roda
  plugin :sessions, secret: "a" * 64
  plugin :route_csrf
  plugin :forme_set, secret: "a" * 64
  plugin :render

  route do |r|
    @expense = Expense.first!

    r.root do
      render inline: <<~ERB
        <% form @expense, method: :post, action: "/update" do |f| %>
          <%= f.input :amount %>
          <%= f.button "Update Amount" %>
        <% end %>
        <% form @expense, method: :post, action: "/update" do |f| %>
          <%= f.input :note %>
          <%= f.button "Update Note" %>
        <% end %>
      ERB
    end

    r.post "update" do
      forme_set(@expense).save

      r.redirect "/"
    end
  end
end

session = Capybara::Session.new(:rack_test, App)
session.visit "/"

session.fill_in "Amount", with: "456"
session.click_on "Update Amount" # performs just fine

session.fill_in "Note", with: "Updated"
session.click_on "Update Note" # ~> SQLite3::ConstraintException: NOT NULL constraint failed: expenses.amount

When I inspect the HTML, the _forme_set_data field in the second form has "columns":["amount", "note"], instead of just ["note"]. I expected forms to be fully self-contained, where rendering one form won't affect the other. Can this be considered a bug?

[janko]

Seems like this is because Forme inputs are being stored on the Sequel model instance, so they persisted from the previous form:

forme/lib/sequel/plugins/forme_set.rb

Lines 22 to 25 in d3b4da5

	def forme_inputs
	return (@forme_inputs || {}) if frozen?
	@forme_inputs ||= {}
	end

[jeremyevans]

This behavior is currently expected, though apparently it isn't listed in the Caveats section of the documentation. In this case, you should avoid using forme_set to handle responses for the route.

However, it may be possible to change things for the Roda forme_set plugin so that the hidden input only includes inputs added to the model object during the form. This will require some care to be backwards compatible, so that only the hidden input is affected, and the model object still has inputs from all forms after processing.

[janko]

If changes could be made for multiple forms to work, in a way that's backwards compatible, that would be great 👌🏻

[jeremyevans]

Agreed. I'll try to work on this this week.

[janko]

Perfect, thanks for the quick fix!