Group and count in Rails

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?

78808 次浏览

小开

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.

小开

最佳答案

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

小开

hash of devise_id as key and associated records count

@project.line_items.group(:device_id).count

小开

something like

 User.all(:joins => :comments, :select => "users.*, count(comments.id) as comments_count", :group => "users.id")

might also work...

小开

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])

小开

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

小开

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'