How to see paging results with Sequel and Sinatra

I am using will_paginate and attempting to page a dataset from Sequel. The requires are:

require 'will_paginate'
require 'will_paginate/sequel'
require 'will_paginate/collection'
require 'will_paginate/version'
require 'sequel/extensions/pagination'

The Ruby code is:

get '/candidate' do
     @items = DB[:candidates].order(:id).extension(:pagination).paginate(1, 10)
     erb :candidate
end

In the view: <%= will_paginate @items %>

The dataset renders correctly with 10 records and when I click "2" or "Next" the address in the browser changes to http://localhost:4567/candidate?page=2 but the records remain the same. Effectively, the results are not paged and I cannot get past page 1.

Solution

The numbers for the page and the number of records are hardcoded in your example using paginate(1, 10), so it will always bring back page 1 with 10 records. You need to pass on the page=2 parameter from the query-string. This is done via the params helper:

get '/candidate' do
  @items = DB[:candidates].order(:id).paginate(:page => params["page"].to_i, :per_page => 10)
  erb :candidate
end

If you wanted, you could also pass on the per_page in the query-string by adding this code:

get '/candidate' do
   @items = DB[:candidates].order(:id).paginate(:page => params["page"].to_i, :per_page => params["per_page"].to_i)
   erb :candidate
end

I'd add a default for both in case they're not given. I understand you can do this via the library, e.g. WillPaginate.per_page = 10, but you could also do this in the route, via:

get '/candidate' do
  page = params.fetch "page", 1
  per_page = params.fetch "per_page", 10
  @items = DB[:candidates].order(:id).paginate(:page => page.to_i, :per_page => per_page.to_i)
  erb :candidate
end

I didn't notice before you were also using the Sinatra helper provided by will_paginate.

I'd either call paginate on the dataset or get a dataset, unpaginated, and pass it to the helper. So either this:

get '/candidate' do
  page = params.fetch "page", 1
  per_page = params.fetch "per_page", 10
  @items = DB[:candidates].order(:id).paginate(:page => page.to_i, :per_page => per_page.to_i)
  erb :candidate
end

# in the view
<%= @items %>

or this:

get '/candidate' do
  @items = DB[:candidates].order(:id)
  erb :candidate
end

# in the view
<%= will_paginate @items, params %>

So, from what I can see, the Sequel paginate method is not overwritten or wrapped/overloaded, so its method signature is the same as it would be if you were just using Sequel and not will_paginate as well. Which means that this code worked for me:

require 'will_paginate'
require 'will_paginate/sequel'
get '/candidate' do
  page = params.fetch "page", 1
  per_page = params.fetch "per_page", 10
  @items = Repo.db[:candidates].order(:id).paginate(page.to_i, per_page.to_i)
  haml :candidate
end

In the Haml view:

- @items.each do |i|
  = i[:title]

Since the method signature is the same I'm not sure what advantage you gain from using will_paginate over Sequel's paginate at all. I couldn't find a way to get the Sinatra helper to work.