Bug: File caching issue - form reuses cached file after validation error

[Skumring]

Bug: File caching issue - form reuses cached file after validation error

Description

When submitting the import form after a validation error, the system reuses the previously cached file instead of showing the "no file" error when no file is selected. This causes confusion and potential unintended data imports.

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Reproduction Script

require 'bundler/inline'

gemfile(true) do
  source 'https://rubygems.org'

  gem 'rails', '~> 7.0.0'
  gem 'sqlite3', '~> 1.6.0'
  gem 'activeadmin', '~> 2.9'
  gem 'active_admin_import', '5.1.0'
  gem 'rchardet', '~> 1.8'
  gem 'rubyzip', '~> 2.3'
  gem 'activerecord-import', '~> 1.5'
end

require 'active_record'
require 'action_controller/railtie'
require 'active_admin'
require 'active_admin_import'

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :authors, force: true do |t|
    t.string :name
    t.string :last_name
    t.timestamps
  end
end

class Author < ActiveRecord::Base
  validates_presence_of :name
end

# Test the caching bug
puts "\n=== Testing File Caching Issue ===\n"

# Create a model instance and simulate form submission
model = ActiveAdminImport::Model.new

# First submission with a file
file = double('file', present?: true, path: '/tmp/test.csv')
model.assign_attributes(file: file)
puts "First submission - file assigned: #{model.file.present?}"

# Simulate validation error by creating a new model without passing file
# This simulates what happens when form is resubmitted without file selection
model2 = ActiveAdminImport::Model.new
model2.assign_attributes({}) # Empty hash, no file key

puts "Second submission - file should be nil: #{model2.file.nil?}"
puts "BUG: File is still present!" unless model2.file.nil?

# The bug: assign_attributes doesn't reset file to nil when not in args
# This causes cached file from previous submission to persist

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Steps to Reproduce (in real application)

1. Visit /admin/authors/import
2. Upload a CSV file with invalid data (e.g., missing required column name)
3. Submit the form → validation error displayed: "can't write unknown attribute" or similar
4. Submit the form again WITHOUT selecting any file

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Expected Behavior

Error message should display: "Please, select file to import"

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Actual Behavior

The system reuses the cached file from step 2, attempting to import it again instead of showing the "no file" error.

---

Root Cause

In model.rb:50, when assign_attributes is called without a :file key in the hash, it doesn't explicitly set file to nil:

def assign_attributes(args = {}, new_record = false)
  @attributes.merge!(args)  # file persists if not in args!
  @new_record = new_record
  # ...
end

When the form is resubmitted without a file, Rails doesn't include the file parameter in the params hash. The assign_attributes method then merges an empty hash with the existing attributes, leaving the previous file in place.

Environment

• Ruby: 3.2.1
• Rails: 7.0.0+ (also affects 5.2, 6.0, 6.1, 7.1)
• ActiveAdmin: 2.9.0
• active_admin_import: 5.1.0 (all versions prior to the fix are affected)
• Database: SQLite3 1.6.0 (but affects all databases)