Why is accepts_nested_attributes_for for :splits behaving differently in Rails 8 compared to Rails 7?

The post content has been automatically edited by the Moderator Agent for consistency and clarity.

I recently rewrote one of my applications in Rails 8, transitioning from a long-maintained Rails 7 version.

The app is a double-entry accounting system (Clients:Books:Accounts:Entries:Splits) originally designed for managing Books for a VFW post, and it uses acts-as-tenant to support multiple VFW posts. The problem arises in the Entry Split section.

Below is the relevant excerpt from my Entry model:

RUBY
class Entry < ApplicationRecord
  belongs_to :book
  acts_as_tenant(:client)
  has_many :splits, -> {order(:account_id)}, dependent: :destroy, autosave: :true, inverse_of: :entry
  
  accepts_nested_attributes_for :splits, 
    :reject_if =>  proc { |att| att[:amount].to_i.zero? && att[:account_id].to_i.zero?},
    allow_destroy: true
...

In Rails 7, when updating an Entry and inserting some debug put statements, I observed log entries similar to:

BASH
17:30:15 web.1  |   ↳ app/controllers/entries_controller.rb:167:in `set_entry`
17:30:15 web.1  |  Parameters: {"numb"=>"", "post_date"=>"2025-01-08", "description"=>"Test Entry", "fit_id"=>"", "splits_attributes"=>#<ActionController::Parameters {"0"=>#<ActionController::Parameters {"id"=>"14567", "action"=>"", "memo"=>"", "amount"=>"-2000", "reconcile_state"=>"n", "account_id"=>"5", "debit"=>"", "credit"=>"20.00", "_destroy"=>"0"} permitted: true>, "1"=>#<ActionController::Parameters {"id"=>"14568", "action"=>"", "memo"=>"", "amount"=>"2000", "reconcile_state"=>"n", "account_id"=>"46", "debit"=>"20.00", "credit"=>"", "_destroy"=>"0"} permitted: true>, "2"=>#<ActionController::Parameters {"id"=>", "action"=>", "memo"=>", "amount"=>"" ...}}

Despite identical code and similar parameters, Rails 8 is not handling the nested attributes for splits as Rails 7 did. I'm looking for insights on any differences or requirements (such as permitted parameters or nested array formatting) that might be causing this behavior in Rails 8.

Any help or suggestions would be appreciated.

Comments 0

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

Below is one likely culprit. In your nested splits parameters you’re getting extra keys (notice the

"action"=>""

in each split record) and empty strings that—when converted with to_i—turn into 0. That in turn makes your reject_if condition fire, or at least not behave as you expect.

Below are two points to check and fix:

Extraneous “action” key:
If your nested form (fields_for “splits_attributes”) is accidentally sending an “action” parameter (perhaps due to a hidden field or a misconfigured form builder), then Rails may be confused about the meaning of that key. In general the nested model shouldn’t have an “action” attribute. Review your form partial and remove any input for “action” so that your nested parameters only include the fields that belong on a split (such as amount, account_id, memo, ...).
Reject_if Proc Evaluating Empty Values:
Your reject_if proc is written as
```
RUBY
proc { |att| att[:amount].to_i.zero? && att[:account_id].to_i.zero? }
```
This means that if the user leaves either field blank (which comes in as an empty string and then to_i gives 0) the entire record is rejected. Depending on your intent this may be too aggressive. Often it’s better to check for blank strings instead:
```
RUBY
accepts_nested_attributes_for :splits,
  reject_if: proc { |att| att['amount'].blank? && att['account_id'].blank? },
  allow_destroy: true
```
This way you’ll only reject if both these values are missing, rather than having empty strings become zeros that accidentally trigger the rejection.

In summary, adjust your nested attributes by (a) ensuring that unexpected keys like "action" are not included in the form, and (b) changing the reject_if logic to be based on blank? rather than to_i.zero? so newly added splits aren’t inadvertently rejected.

Try these changes and see if your nested split updates work as expected in Rails 8.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by CelestialCaptain193 • 2 months ago

Well I said I was a hobbyist and not an expert. It took a couple days to figure it out.

When I created the new app I used bin/rails g scaffold (model, attributes)on the models ( Clients:Books:Accounts:Entries:Splits) to have a clean rails 8 version. I then went through a process to move over any non scaffold stuff to the controllers and models.

In the rails 7 version the Entry entry_params was:

RUBY
   # Never trust parameters from the scary internet, only allow the white list through.
    def entry_params
      params.require(:entry).permit(:numb, :post_date, :description, :fit_id, :book_id,
        splits_attributes: [:id,:action,:memo,:amount,:reconcile_state,:account_id,:debit,:credit,:_destroy])
    end

On rails 8 version it was:

RUBY
    # Only allow a list of trusted parameters through.
    def entry_params
      params.expect(entry: [ :client_id, :book_id, :numb, :post_date, :description, :fit_id, :lock_version,
        splits_attributes: [:id,:action,:memo,:amount,:reconcile_state,:account_id,:debit,:credit,:_destroy] ])
    end

I found a post that tried to explain the differences convert to params.expect

Why it didn't work was that Splits is actually an array of Splits. The params.expect uses an array to define attributes. After a little search through the post you define array of models with double brackets [[ :a, :b, :etc]]. The fixed version of entry_params is:

RUBY
    def entry_params
      params.expect(entry: [ :client_id, :book_id, :numb, :post_date, :description, :fit_id, :lock_version,
        splits_attributes: [[:id,:action,:memo,:amount,:reconcile_state,:account_id,:debit,:credit,:_destroy]] ])
    end

Maybe the Rail 8 g scaffold should see if has_many :splits is in the Entry model, it should use double brackets!

Thanks for the few comments - they did help.

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Why is accepts_nested_attributes_for for :splits behaving differently in Rails 8 compared to Rails 7?

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