when doing a ActiveRecord::Base count how do i order by count desc?

问题

an example would be...

Pets.find(:all, :select => 'count(*) count, pet_type', :group => 'pet_type', :order => 'count')

returns the correct results but not the actual counts in the orderedhash object returned.

Pets.count(:all, :group => 'pet_type')

returns the count but are not sorting in a descending fashion... how would i do this?

I think i'd prefer to use .find .. but i'll take .count if i can sort it.

回答1:

Pets.find(:all, :select => '*, count(*) AS count, pet_type', :group => 'pet_type', :order => 'count')

回答2:

Pets.find(:all, :select => 'count(*) count, pet_type', :group => 'pet_type', :order => 'count DESC')

回答3:

This works fine with MySQL but might not transfer well if you switch DBs:

Pets.count(:all, :group => 'pet_type', :order => 'count(*) DESC')

回答4:

@pets=Pets.include(:meals_per_days).sort do |a,b| 
  a.meals_per_days.size <=> b.meals_per_days.size
end

Note : This will returns an array of records, not an ActiveRecord:Relation.

Note2 : Use size, not count, as count will execute sql calls to the db.

来源：https://stackoverflow.com/questions/4207889/when-doing-a-activerecordbase-count-how-do-i-order-by-count-desc