86

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?

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7 Answers 7

Reset to default
162

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
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2
  • 1
    This gives a warning: 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':)
    – Chloe
    Commented Dec 23, 2013 at 22:21
  • 7
    @Chloe - Try this in Rails 4 to remove the warning: @project.line_items.group(:device_id).count
    – Matt Huggins
    Commented Jan 7, 2014 at 21:01
24

hash of devise_id as key and associated records count

@project.line_items.group(:device_id).count
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14

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'

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10

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.

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2
  • hrm, I put debug(@line_items) in my view, but I don't see any counts, so I don't think I'm understanding you. I think the output is exactly the same as without the select option.
    – tladuke
    Commented Jan 7, 2010 at 18:04
  • The debug method won't show the count because it's not an ActiveRecord attribute, but there is a count attribute on each object. In any case, Chandra's solution is much better.
    – Alex Reisner
    Commented Jan 27, 2010 at 0:52
4

something like

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

might also work...

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1

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])
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1

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
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2
  • 1
    They will return completely different results for enumerated attributes. For example: 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
    – msdundar
    Commented Oct 16, 2017 at 12:15
  • true, how about uniq then? @project.line_items.pluck(:device_id).uniq.count
    – John Smith
    Commented Nov 10, 2017 at 9:44

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