Handle nullable foreign key in multiselect

[jibidus]

has_many with not nullable foreign may raise exception when user try to remove elements from corresponding association.
The aim of this request is to prevent such behavior with disabling remove actions from form.

[mshibuya]

Thanks for your work! 🍺

[arnvald]

@jibidus @mshibuya it seems that this PR breaks has_many :through relation 😢

I've got relation:

promotion has many user_promotions
promotion has many users through user_promotions

when I'm opening view to add new promotion, I can add users there, and what happens during this code execution:

def foreign_key_nullable?
  return if foreign_key.nil? || type != :has_many
  klass.columns_hash[association.foreign_key].null
end

is that foreign_key is present (:user_id), relation type is :has_many, but klass.columns_hash does not contain "user_id" therefore it returns nil and the error is undefined method "null" for nil:NilClass

Any idea how to fix it?

[jibidus]

@arnvald Let me have a look.

[jibidus]

@arnvald I didn't manage to reproduce the issue 😩 .
When exactly the issue is raised? When you add user to new promotion ?
Do you have a RSpec test to be sure I can reproduce this issue?

[arnvald]

@jibidus I created a simple application here: https://github.com/arnvald/rails_admin_polymorphic_bug

To reproduce:

1. bundle install
2. bin/rake db:create db:migrate
3. bin/rails s
4. go to http://localhost:3000/admin/user/new

I'll try to write a spec that'll cover this case, either today or tomorrow.

[mshibuya]

@jibidus @arnvald Opened as a new issue: #2474

[jibidus]

@arnvald @mshibuya Pull Request created to fix this issue: #2478.
Sorry for the issue and the delay 😟 .

[arnvald]

@jibidus thanks for fixing the bug!

[grillermo]

How can i configure this manually? i want some has_many fields without those buttons to remove the association. But adding

    field :addresses do
      removable? do
        false
      end
    end

Does nothing.

[jibidus]

This Pull Request was designed to prevent displaying the Remove button when foreign key is not nullable.
So, if make your foreign key not nullable, the Remove button will disappear.
If you don't want to make your foreign key not nullable, I think you cannot do that (hide Remove button).

[grillermo]

I made my own custom field for my use case, i don't want the foreign key nullable i wanted that field to not have that remove button on that particular model, so this is what i did:
https://gist.github.com/grillermo/9c0e5521a5e5b9361846128eb272c8c0
Thanks for the answer