`IgnorableColumn` module in `app/models/concerns/ignorable_column.rb`
which is used in models to ignore dealing with specified columns.

In Rails 5 with this [pull
request](https://github.com/rails/rails/pull/21720),
`self.ignored_columns` was introduced to do this job.

For example, in app/models/user.rb:

```ruby
ignore_column :external_email
ignore_column :email_provider
```

can be changed to:

```ruby
self.ignored_columns = %i[external_email email_provider]
```