How can I count the result of an ActiveRecord .group query? Chaining .count returns a hash

Question

I can use the following :

User.where(\"zip_code = \'48104\'\").group(\'users.id\').count

To get hashes like :

{195=>1, 1         


        

Answer 1

As said before by orourkedd the accepted answer is not great when dealing with a large amount of records. I too recently encountered this issue and have large tables that I definitely don't want to load into memory. So here is what works for me.

users=User.where("zip_code = '48104'").group('users.id')
user_count=User.where(id: users.select(:id)).count

Rails will handle the users.select part like a subquery. This works with Rails 4

Answer 2

The accepted answer is not scalable. Using @robbrit's method on a query with 25,000 matching users would pull 25,000 results (ie an array with 25,000 elements) into memory and then count the elements array. Here is a method that will do it without pulling all that data:

def count_query(query)
  query = "SELECT count(*) AS count_all FROM (#{query.to_sql}) x"
  ActiveRecord::Base.connection.execute(query).first.try(:[], 0).to_i
end

It is used like this:

query = User.where("zip_code = '48104'").group('users.id')
count = count_query(query)

This works for me using mysql, btw.

It was inspired by this guy: https://github.com/mrbrdo/active_record_group_count/blob/master/lib/active_record_group_count/scope.rb

Answer 3

If you want to add the values of the hashes together then:

{key1: 1, key2: 2}.values.inject(:+) # => 3

If you just want the number of keys then:

{key1: 1, key2: 2}.length # => 2

Answer 4

Since the first count() is returning a hash, use whatever Ruby enumerable operations you wish on it. Example:

User.where("zip_code = '48104'").group('users.id').count.count

See also:

• http://ar.rubyonrails.org/classes/ActiveRecord/Calculations/ClassMethods.html#M000292
• http://ruby-doc.org/core-1.9.3/Enumerable.html#method-i-count

Answer 5

Try:

User.where("zip_code = '48104'").group('users.id').count.length

Answer 6

Another way, useful if the values can be > 1.

User.where("zip_code = '48104'").group('users.id').count.values.sum