fix: declare the coder for the custom column

gemfiles/rails6.gemfile

@@ -12,5 +12,5 @@ group :test do
   gem 'factory_bot'
   gem 'rspec'
   gem 'shoulda-matchers'
-  gem 'sqlite3'
+  gem 'sqlite3', '~> 1.4'
 end

lib/attach/attachment.rb

@@ -25,7 +25,7 @@ class Attachment < ActiveRecord::Base
     validates :digest, presence: true
     validates :token, presence: true, uniqueness: { case_sensitive: false }
 
-    serialize :custom, type: Hash, default: {}
+    serialize :custom, coder: YAML, type: Hash, default: {}
 
     before_validation :set_token
     before_validation :set_digest

spec/spec_helper.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'logger'
 require 'active_record'
 require 'shoulda-matchers'
 require 'factory_bot'
@@ -10,8 +11,10 @@
 ActiveRecord::Base.include Attach::ModelExtension
 
 ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'
-ActiveRecord::MigrationContext.new(File.expand_path('../db/migrate', __dir__),
-                                   ActiveRecord::SchemaMigration).migrate(nil)
+migration_context_args = [File.expand_path('../db/migrate', __dir__)]
+# Active Record < 7.1 needs the schema migration class; 7.1+ takes it from the connection
+migration_context_args << ActiveRecord::SchemaMigration if ActiveRecord.version < Gem::Version.new('7.1')
+ActiveRecord::MigrationContext.new(*migration_context_args).migrate(nil)
 ActiveRecord::Migration.create_table :users do |t|
   t.string :name
   t.datetime :suspended_at