Grid:

class DocumentsGrid

  include Datagrid

  scope do
    Document.desc(:created_at)
  end

  filter :rating, :enum, :select => 0..10
  filter :title, :header => "Title (contains)" do |value|
    where(:title => /#{Regexp.escape(value)}/i)
  end
  filter :author, :header => "Author (regexp)" do |value|
    begin
      where(:author => Regexp.compile(value))
    rescue RegexpError
      where
    end
  end

  filter :condition, :dynamic, :header => "Dynamic condition"
  column :title 
  column :author 
  column :rating 
  column :created_at do
    self.created_at.to_date
  end

end

Controller:

class DocumentsController < ApplicationController

  def index
    @documents_grid = DocumentsGrid.new(params[:documents_grid]) do |scope|
      scope.page(params[:page])
    end
  end
end

View:

<h3>Documents Grid</h3>

<div class="left">
  <%= datagrid_form_for @documents_grid, url: documents_path %>

  <div class='total'>Total: <%= @documents_grid.assets.count %></div>
  <%= datagrid_table(@documents_grid) %>
  <%= paginate @documents_grid.assets %>
</div>

<div class="right">
  <%= render :partial => "shared/source", :object => @documents_grid %>
</div>