Question

I have a ruby on rails 3 project in which I query for a certain number of objects by using a .limit(3) . Then, in my view, I loop through these objects. After that, if there are 3 objects in the view, I display a “load more” button. Here is the view code:

<% @objects.each do |object| %>
  <%= render object._type.pluralize.underscore + '/teaser', :object => object %>
<% end %>
<% if @objects.size(true) == 3 %>
  #load more link here
<% end %>

The size(true) is passed a boolean to ensure that mongoID takes into account the .limit and .offset on my query (otherwise it returns the total number of objects that matched, regardless of the limit / offset). Here are the relevant development log lines:

MONGODB project_development['system.indexes'].insert([{:name=>"_public_id_1", :ns=>"project_development.objects", :key=>{"_public_id"=>1}, :unique=>true}])
MONGODB project_development['objects'].find({:deleted_at=>{"$exists"=>false}}).limit(3).sort([[:created_at, :desc]])
#some rendering of views
MONGODB project_development['system.indexes'].insert([{:name=>"_public_id_1", :ns=>"project_development.objects", :key=>{"_public_id"=>1}, :unique=>true}])
MONGODB project_development['$cmd'].find({"count"=>"objects", "query"=>{:deleted_at=>{"$exists"=>false}}, "limit"=>3, "fields"=>nil})

My question is: does MongoID do a separate query for my @objects.size(true)? I imagine the ['$cmd'] might indicate otherwise, but I’m not sure.

Answer 1

I don’t think so, there was a pull request month ago to add aliases for :size, :length to :count to avoid re-running queries. You can check that.