I know I've seen this before but I can't find anything now. I want to group a query by a certain column and be able to display how many are in each group. I got the first part down:
@line_items = @project.line_items.all(:group => "device_id") This is for my line item index view, which is just a table displaying the line items. How do I make a column in that table for "count" now that the line items are grouped by device?
You can do count on line_items which will return you an ordered hash of device_id and count.
@project.line_items.group(:device_id).count 
DEPRECATION WARNING: Relation#calculate with finder options is deprecated. Please build a scope and then call calculate on it instead. (called from C:in 'count':)
@project.line_items.group(:device_id).counthash of devise_id as key and associated records count
@project.line_items.group(:device_id).count I think you can try this as well.
@project.line_items.group(:device_id).pluck("device_id, count(device_id)") ^^ This gives array of arrays with elements 'device_id and count'
Just add a :select option:
@line_items = @project.line_items.all( :group => "device_id", :select => "device_id, COUNT(*) as count" ) Then each @line_item will have a count attribute.
something like
User.all(:joins => :comments, :select => "users.*, count(comments.id) as comments_count", :group => "users.id") might also work...
After this commit:
https://github.com/rails/rails/commit/a1c05dd8b9bd3623289d3aa73dda2943d620cc34
there's a new way to do the same thing:
@project.line_items.count(:group => LineItem.arel_table[:device_id]) For only count pluck would be faster here rather than group
@project.line_items.pluck(:device_id).count @project.line_items.pluck(:device_id).uniq.count 
customer_subscriptions.group(:status).count will return: {1 => 6, 2 => 11, 3 => 136, 0 => 30} and customer_subscriptions.pluck(:status).count will just return 183