• Uninstall the legacy gem and replace it with gem "pagy" in the Gemfile.
• Add include Pagy::Method statement to the application controller.

• Search for the class name of the legacy gem, for example WillPaginate or Kaminari. You should find most of the code relative to global gem configuration or monkey patching.
• Remove all the legacy settings of the old gem.

Look for terms like per_page, per, and similar, as these are configuration settings. Include them in the appropriate paginator call in the controller (e.g., pagy(:offset, collection, limit: 10)) or globally in the Pagy initializer (e.g., Pagy::OPTIONS[:limit] = 10).

If the app uses the page scope in model methods or scopes, remove it, along with the argument used to pass the page number, while preserving the rest of the scope. Locate where the app applies this paginated scope in the controllers and replace it with the scope in a paginator statement. For example:

#@records = Product.paginated_scope(params[:page])
@pagy, @records = pagy(:offset, Product.non_paginated_scope)

In controllers, legacy pagination statements generally map directly to Pagy, making them straightforward to convert.

Search for keywords like page and paginate statements and use the pagy(:offset, ...) paginator instead. For example:

#@records = Product.some_scope.page(params[:page])
#@records = Product.paginate(:page => params[:page])

@pagy, @records = pagy(:offset, Product.my_scope)

#@records = Product.some_scope.page(params[:page]).per(15)
#@records = Product.some_scope.page(params[:page]).per_page(15)
#@records = Product.paginate(page: params[:page], per_page: 15)

@pagy, @records = pagy(:offset, Product.all, limit: 15)

Similarly, in views, legacy pagination statements typically correspond directly to Pagy, simplifying conversion.

Search for keywords like will_paginate and paginate statement and use one of the series_nav methods. For example:

<%= will_paginate @records %>
<%= paginate @records %>

<%== @pagy.series_nav %>