将will_paginate与多个模型一起使用（Rails）

Question

Pretty sure that I'm missing something really simple here:

I'm trying to display a series of pages that contain instances of two different models - Profiles and Groups. I need them ordering by their name attribute. I could select all of the instances for each model, then sort and paginate them, but this feels sloppy and inefficient.

I'm using mislav-will_paginate, and was wondering if there is any better way of achieving this? Something like:

[Profile, Group].paginate(...)

would be ideal!

Answer 1

Good question, I ran into the same problem a couple of times. Each time, I ended it up by writing my own sql query based on sql unions (it works fine with sqlite and mysql). Then, you may use will paginate by passing the results ( http://www.pathf.com/blogs/2008/06/how-to-use-will_paginate-with-non-activerecord-collectionarray/ ). Do not forget to perform the query to count all the rows.

Some lines of code (not tested)

my_query = "(select posts.title from posts) UNIONS (select profiles.name from profiles)"
total_entries = ActiveRecord::Base.connection.execute("select count(*) as count from (#{my_query})").first['count'].to_i

results = ActiveRecord::Base.connection.select_rows("select * from (#{my_query}) limit #{limit} offset #{offset}")

Is it overkilled ? Maybe but you've got the minimal number of queries and results are consistent.

Hope it helps.

Note: If you get the offset value from a http param, you should use sanitize_sql_for_conditions (ie: sql injection ....)

Answer 2

You can get close doing something like:

@profiles, @groups = [Profile, Group].map do |clazz|
  clazz.paginate(:page => params[clazz.to_s.downcase + "_page"], :order => 'name')
end

That will then paginate using page parameters profile_page and group_page . You can get the will_paginate call in the view to use the correct page using:

<%= will_paginate @profiles, :page_param => 'profile_page' %>
....
<%= will_paginate @groups, :page_param => 'group_page' %>

Still, I'm not sure there's a huge benefit over setting up @groups and @profiles individually.

Answer 3

in my last project i stuck into a problem, i had to paginate multiple models with single pagination in my search functionality. it should work in a way that the first model should appear first when the results of the first model a second model should continue the results and the third and so on as one single search feed, just like facebook feeds. this is the function i created to do this functionality

def multi_paginate(models, page, per_page)

  WillPaginate::Collection.create(page, per_page) do |pager|

    # set total entries
    pager.total_entries = 0
    counts = [0]
    offsets = []
    for model in models
          pager.total_entries += model.count
          counts << model.count
          offset = pager.offset-(offsets[-1] || 0)
          offset = offset>model.count ? model.count : offset 
          offsets << (offset<0 ? 0 : offset)
    end

    result = []
    for i in 0...models.count
          result += models[i].limit(pager.per_page-result.length).offset(offsets[i]).to_a
    end

    pager.replace(result)
  end

end

try it and let me know if you have any problem with it, i also posted it as an issue to will_paginate repository, if everyone confirmed that it works correctly i'll fork and commit it to the library. https://github.com/mislav/will_paginate/issues/351

Answer 4

Have you tried displaying two different sets of results with their own paginators and update them via AJAX? It is not exactly what you want, but the result is similar.